KR20200126351A - Lithium battery - Google Patents

Abstract

The present invention relates to a lithium battery comprising: a positive electrode; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises a nickel-based lithium transition metal oxide having an average particle diameter of 2 μm or more of primary particles, and the negative electrode comprises graphite and a silicon-based compound. More specifically, the lithium battery has improved discharge capacity and service life properties.

Description

Lithium battery {Lithium battery}

It relates to a lithium battery.

In order to meet the miniaturization and high performance of various devices, high energy density in addition to miniaturization and weight reduction of lithium batteries is becoming important. That is, high-capacity lithium batteries are becoming more important.

In order to implement a lithium battery suitable for the above use, a lithium battery including a positive electrode active material and a negative electrode active material having a high capacity and excellent lifespan characteristics have been studied.

A typical example of a negative active material for lithium batteries is a carbon-based material such as graphite. Graphite has excellent capacity retention characteristics and potential characteristics, and there is no change in volume when forming an alloy with lithium, so the stability of the battery is high, but the electric capacity is small.

As an anode active material having a higher electric capacity than a carbon-based material, a metal alloyable with lithium, an alloy thereof, or an oxide thereof may be used. For example, lithium alloyable metals are Si, Sn, Al, and the like. Metals that can be alloyed with lithium have a very large electric capacity but have poor lifespan characteristics.

A representative example of a cathode active material for lithium batteries is LiCoO ₂ . LiCoO ₂ has excellent life characteristics but small electric capacity.

Complex transition metal oxides such as LiNi _x Co _y Mn _z O ₂ (0<x<1, 0<y<1, 0<z<1) have increased electric capacity compared to LiCoO ₂ but have poor lifespan characteristics. .

Therefore, there is still a need for a lithium battery having a high capacity and improved lifespan characteristics.

One aspect is to provide a lithium battery with a new composition.

According to one aspect,

anode; cathode; And an electrolyte disposed between the positive electrode and the negative electrode,

The anode comprises a nickel-based lithium transition metal oxide and a lithium cobalt oxide having an average particle diameter of 2 μm or more of the primary particles,

A lithium battery is provided in which the negative electrode includes graphite and a silicon-based compound.

According to one aspect, discharge capacity and life characteristics of a lithium battery may be improved by including a positive electrode and a negative electrode having a new composition.

1 is an SEM image of a nickel-based lithium transition metal oxide prepared in Preparation Example 1. FIG.
2 is an SEM image of a nickel-based lithium transition metal oxide according to Comparative Preparation Example 1.
3 is a differential scanning calorimeter analysis graph of the nickel-based lithium transition metal oxide prepared in Preparation 1 and Comparative Preparation Example 1. FIG.
4 is a schematic diagram of a lithium battery according to an embodiment.
<Explanation of symbols for major parts of drawings>
1: lithium battery 2: negative electrode
3: anode 4: separator
5: battery case 6: cap assembly

Hereinafter, a lithium battery according to an exemplary embodiment will be described in more detail.

A lithium battery according to an embodiment includes a positive electrode; cathode; And an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode includes a nickel-based lithium transition metal oxide and a lithium cobalt oxide having a particle diameter of 2 μm or more of the primary particles, and the negative electrode includes graphite and a silicon-based compound.

The lithium battery includes nickel-based lithium transition metal oxide and lithium cobalt oxide in the form of a single particle having a particle diameter of 2 μm or more as a positive electrode active material in the positive electrode, and graphite and silicon-based compounds are simultaneously used as negative electrode active materials in the negative electrode. By including it, it is possible to provide high discharge capacity and improved life characteristics at the same time.

By including nickel-based lithium transition metal oxide and lithium cobalt oxide in the form of single particles having a particle diameter of 2 μm or more in the positive electrode of the lithium battery, the mixture density of the positive electrode increases, resulting in the discharge capacity of the lithium battery. Can be increased. In addition, by using the positive electrode, gas generation at a high voltage is reduced and thermal stability is improved, so that a lithium battery with improved life characteristics can be obtained.

In the lithium battery, the initial charge/discharge efficiency of the positive electrode including nickel-based lithium transition metal oxide and lithium cobalt oxide in the form of a single particle having a particle diameter of 2 μm or more is equal to the initial charge/discharge efficiency of the negative electrode, or Can be higher. In the lithium battery, when the initial charging/discharging efficiency of the positive electrode is lower than that of the negative electrode, the high mixture density of the nickel-based lithium transition metal oxide in the form of a single particle having a particle diameter of 2㎛ or more of the primary particle The increase in discharge capacity per unit volume can be offset by low charge/discharge efficiency.

The content of the silicon-based compound in the lithium battery may be 5% by weight or more based on the total weight of graphite and the silicon-based compound. For example, the content of the silicon-based compound in the lithium battery may be 5 to 25% by weight based on the total weight of the graphite and the silicon-based compound. If the content of the silicon-based compound in the lithium battery is less than 5% by weight, the initial charging/discharging efficiency of the negative electrode is higher than that of the positive electrode, and the discharge capacity of the lithium battery may be reduced.

For example, the silicon-based compound may be a silicon metal (metalloid), an alloy of silicon and another metal, or a silicon oxide, but is not necessarily limited thereto, and any one that can be used as a silicon-based compound in the art may be used.

For example, the silicon-based compound is Si, an Si-Y alloy (the Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination element thereof, but not Si), SiO _a (0<a<3), etc.

For example, the silicon-based compound may be a silicon oxide represented by Formula 1:

<Formula 1>

SiO _x

In the above formula, 0<x<2.0.

For example, in the lithium battery, the nickel-based lithium transition metal oxide may be a compound represented by the following Formula 2:

<Formula 2>

Li _x Co _a Ni _b M _c O _2+α

In the above formula, 0.9<x<1.5, 0<a<0.5, 0<b<1, 0<c<1, -0.1≤α≤0.1, and M is Mg, Ca, Sr, Ba, Ti, Zr, Nb , Mo, W, Zn, Al, Si, Mn, Cr, Fe, Mg, Sr, V, and at least one element selected from the group consisting of rare earth elements.

For example, in the lithium battery, the nickel-based lithium transition metal oxide may be a compound represented by the following Formula 3:

<Formula 3>

Li _x Co _a Ni _b Mn _c O _2+α

In the above formula, 0.9<x<1.1, 0<a<0.5, 0.4<b<1, 0<c<0.5, -0.1≦α≦0.1.

For example, in the lithium battery, the nickel-based lithium transition metal oxide may be a compound represented by Formula 4:

<Formula 4>

Li _x Co _a Ni _b Mn _c O ₂

In the above formula, 0≤x<1.1, 0.1<a<0.3, 0.4<b<0.6, 0.2<c<0.4.

In the differential scanning calorimeter analysis of the nickel-based lithium transition metal oxide in the form of a single particle in the lithium battery, the onset point temperature is 250 to 270°C. Compared to the conventional NCM, the onset point temperature is higher and the instantaneous emission amount of the main peak is reduced. Have. By exhibiting such characteristics, high temperature stability of a lithium battery including the nickel-based lithium transition metal oxide may be improved.

For example, the average primary particle diameter of the nickel-based lithium transition metal oxide in the form of a single particle may have a particle diameter of 2 μm to 5 μm. For example, the average primary particle diameter of the nickel-based lithium transition metal oxide in the form of a single particle may have a particle diameter of 3 μm to 5 μm. If the primary particle diameter is less than 1 μm, the density of the mixture may be lowered or the high rate characteristics may be lowered. If the primary particle diameter is too large, the density of the mixture may be lowered.

In the lithium battery, when the size of the primary particles of the nickel-based lithium transition metal oxide in the form of a single particle is adjusted to implement a lithium battery using the same, the amount of gas generated at high voltage can be reduced and reliability and safety can be secured.

The nickel-based lithium transition metal oxide in the form of a single particle may be fired at a high temperature of 1000°C or higher to reduce a specific surface area and remove residual lithium as much as possible, thereby suppressing a side reaction between the residual lithium and the electrolyte. And, as described above, by firing at a high temperature, the crystallinity of the nickel-based lithium transition metal oxide is improved, and stability at a high voltage may be ensured.

In the single-particle type of nickel-based lithium transition metal oxide, the content of LiOH, which is residual lithium, may be 0.01 to 0.06% by weight, and the content of Li ₂ CO ₃ may be 0.05 to 0.1% by weight. Here, the contents of LiOH and Li ₂ CO ₃ were measured through a titration method.

In the single particle form of nickel-based lithium transition metal oxide, the content of lithium carbonate through GC-MS analysis may be 0.01 to 0.05% by weight.

As described above, when the content of the residual lithium is small, side reactions between the residual lithium and the electrolyte may be suppressed, and generation of gas at high voltage and high temperature may be suppressed. In addition, if the content of LiOH is low, the pH value of the slurry is lowered in the positive electrode slurry manufacturing process, making the positive electrode slurry in a stable state, enabling a uniform electrode plate coating operation.

In the lithium battery, the positive electrode may additionally include lithium cobalt oxide. By appropriately adding the lithium cobalt oxide, the charge/discharge characteristics of the lithium battery may be further improved.

For example, the content of lithium cobalt oxide in the positive electrode of the lithium battery may be 65% by weight or more based on the total weight of the nickel-based lithium transition metal oxide and the lithium cobalt oxide. For example, the content of lithium cobalt oxide in the positive electrode of the lithium battery may be 65% by weight to 95% by weight based on the total weight of the nickel-based lithium transition metal oxide and the lithium cobalt oxide. For example, the content of lithium cobalt oxide in the positive electrode of the lithium battery may be 70% by weight to 90% by weight based on the total weight of the nickel-based lithium transition metal oxide and the lithium cobalt oxide. Further improved battery characteristics may be implemented in the above content range.

At least a part of the lithium cobalt oxide may be doped with nickel. As the lithium cobalt oxide is additionally doped with nickel, the charging capacity of the lithium cobalt oxide may increase.

The content of nickel doped in the lithium cobalt oxide may be 20 mol% or less with respect to the total mol number of nickel and cobalt. For example, the amount of nickel doped in the lithium cobalt oxide may be 0.5 mol% to 20 mol% based on the total number of mols of nickel and cobalt. For example, the content of nickel doped in the lithium cobalt oxide may be 0.5 mol% to 10 mol% with respect to the total mol number of nickel and cobalt. For example, the content of nickel doped in the lithium cobalt oxide may be 0.5 mol% to 5 mol% based on the total number of moles of nickel and cobalt.

If the amount of nickel doped in the lithium cobalt oxide is too small, the increase in charging capacity is insignificant, and if the content of nickel doped in the lithium cobalt oxide is too large, the charge/discharge voltage of the lithium cobalt oxide may decrease. When the lithium cobalt oxide is doped with nickel, the density of the mixture may increase compared to the case of simply mixing the lithium cobalt oxide with the lithium nickel oxide.

In the lithium battery, the initial charge/discharge efficiency of the positive electrode may be 91.5% or less. When the half cell including the positive electrode is charged at a constant current with a current of 0.1C with respect to lithium metal until the voltage reaches 4.4V (vs. Li), and the current becomes 0.01C while maintaining 4.4V After charging with a constant voltage up to and then discharging with a constant current of 0.1C until the voltage reaches 3.0V (vs. Li) during discharge, the initial charge/discharge efficiency may be 88.5% or more. If the initial charge/discharge efficiency of the positive electrode exceeds 88.5%, the discharge capacity may decrease. For example, in the lithium battery, the initial charge/discharge efficiency of the positive electrode may be 88% or less. For example, in the lithium battery, the initial charge/discharge efficiency of the positive electrode may be 87% or less. For example, in the lithium battery, the initial charge/discharge efficiency of the positive electrode may be 87% or less.

In the lithium battery, the mixture density of the positive electrode may be 3.5 g/cc or more. For example, in the lithium battery, the mixture density of the positive electrode may be 3.5g/cc to 3.9g/cc. For example, in the lithium battery, the mixture density of the positive electrode may be 3.7g/cc to 3.9g/cc. Since the positive electrode contains a nickel-based lithium transition metal oxide in the form of a single particle, it has an increased mixture density compared to 3.3 to 3.5 g/cc of a positive electrode containing a nickel-based lithium transition metal oxide other than the conventional e-single particle. Thus, it is possible to provide an improved discharge capacity per volume.

In the lithium battery, the initial charge/discharge efficiency of the negative electrode may be 88.0% or less. The half cell including the negative electrode is charged at a constant current with a current of 0.1C for the lithium metal and for the lithium metal until the voltage reaches 0.01V (vs. Li), and the current is 0.01V while maintaining 0.01V. When the constant voltage is charged until C, and then discharged with a constant current of 0.1C until the voltage reaches 1.5V (vs. Li) during discharge, the initial charge/discharge efficiency may be 88.0% or less. In the lithium battery, since the negative electrode has a low initial charge/discharge efficiency of 88.0% or less, a positive electrode having a low initial charge/discharge efficiency can be used without loss of discharge capacity.

In the lithium battery, the initial charging capacity of the positive electrode may be 200 mAh/g or more. The half cell including the positive electrode is charged at a constant current with a current of 0.1C for the lithium metal and for the lithium metal until the voltage reaches 4.5V (vs. Li), and the current is maintained at 4.5V. When the constant voltage is charged to 0.01C and then discharged with a constant current of 0.1C until the voltage reaches 3.0V (vs. Li) during discharge, the initial charging capacity may be 200mAh/g or more.

The lithium battery may be manufactured as follows.

First, the positive electrode includes a nickel-based lithium transition metal oxide and a lithium cobalton oxide having a particle diameter of 1 μm or more of the aforementioned primary particles as a positive electrode active material.

The positive electrode is, for example, prepared by mixing the above-described positive electrode active material, conductive agent, binder, and solvent to prepare a positive electrode active material composition. The positive electrode active material composition may be directly coated and dried on an aluminum current collector to prepare a positive electrode plate having a positive electrode active material layer formed thereon. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film obtained by peeling from the support may be laminated on the aluminum current collector to prepare a positive electrode plate having a positive electrode active material layer.

Conductive agents include carbon black, graphite fine particles, natural graphite, artificial graphite, acetylene black, Ketjen black, carbon fiber; Carbon nanotubes; Metal powders such as copper, nickel, aluminum, silver, or metal fibers or metal tubes; Conductive polymers such as polyphenylene derivatives may be used, but are not limited thereto, and any material that can be used as a conductive material in the art may be used.

As a binder, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene (PTFE), a mixture of the aforementioned polymers, styrene butadiene rubber type A polymer or the like may be used, and N-methylpyrrolidone (NMP), acetone, water, and the like may be used as the solvent, but are not necessarily limited thereto, and any solvent that can be used in the art may be used.

In some cases, it is also possible to form pores inside the electrode plate by adding a plasticizer to the positive electrode active material composition.

The contents of the composite positive electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium batteries. Depending on the use and configuration of the lithium battery, one or more of the conductive material, the binder, and the solvent may be omitted.

In addition, the positive electrode may additionally include a general positive electrode active material having at least one different in composition, particle diameter, and physical properties in addition to the nickel-based lithium transition metal oxide having a particle diameter of 1 μm or more of the primary particles described above.

The general positive electrode active material is a lithium-containing metal oxide and may be used without limitation as long as it is commonly used in the art. For example, one or more of a complex oxide of a metal and lithium selected from cobalt, manganese, nickel, and combinations thereof may be used, and a specific example thereof is Li _a A _1-b B _b D ₂ (the Where 0.90≦a≦1, and 0≦b≦0.5); Li _a E _1-b B _b O _2-c D _c (wherein 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05); LiE _2-b B _b O _4-c D _c (where 0≦b≦0.5, 0≦c≦0.05); Li _a Ni _1-bc Co _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Co _b B _c O _2-α F ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b B _c D _α (wherein, 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li _a Ni _1-bc Mn _b B _c O _2-α F _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (In the above formula, 0.90≦a≦1, 0.001≦b≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); A compound represented by any one of the formulas of LiFePO ₄ can be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _1-x Mn _x O _2x (0<x<1), LiNi _1-xy Co _x Mn _y O ₂ (0≤x≤ 0.5, 0≤y≤0.5), FePO ₄ and the like.

Of course, one having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may contain a coating element compound of oxide, hydroxide, oxyhydroxide of coating element, oxycarbonate of coating element, or hydroxycarbonate of coating element. The compound constituting these coating layers may be amorphous or crystalline. As a coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. The coating layer formation process may be any coating method as long as the compound can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements (e.g. spray coating, dipping method, etc.). Since the content can be well understood by those engaged in the relevant field, detailed description will be omitted.

Next, the negative electrode can be manufactured as follows. The negative electrode may be manufactured in the same manner as the positive electrode, except that a negative electrode active material is used instead of the positive electrode active material. In addition, in the negative electrode active material composition, the same conductive agent, binder, and solvent as in the case of the positive electrode may be used. The negative electrode includes graphite and a silicon-based compound as a negative electrode active material.

For example, a negative electrode active material composition may be prepared by mixing a negative electrode active material, a conductive agent, a binder, and a solvent, and the negative electrode plate may be manufactured by directly coating this on a copper current collector. Alternatively, a negative electrode plate may be manufactured by casting the negative active material composition on a separate support and laminating a negative electrode active material film peeled from the support on a copper current collector.

In addition, the negative electrode may additionally include a general negative electrode active material having one or more different in composition, particle diameter, and physical properties with the above-described graphite and silicon-based compounds.

The other general negative electrode active material may be any material that can be used as a negative electrode active material for lithium batteries in the art. For example, it may include at least one selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, and a carbon-based material.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth Element or a combination element thereof, not Si), Sn-Y alloy (the Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, not Sn ), etc. The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be Se, Te, Po, or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like.

For example, the non-transition metal oxide may be SnO ₂ , SiO _x (0<x<2), or the like.

The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and the amorphous carbon is soft carbon (low temperature calcined carbon) or hard carbon (hard carbon). carbon), mesophase pitch carbide, calcined coke, or the like.

The contents of the negative electrode active material, the conductive agent, the binder, and the solvent are the levels commonly used in lithium batteries.

Next, a separator to be inserted between the positive and negative electrodes is prepared. Any of the separators can be used as long as they are commonly used in lithium batteries. Those having low resistance to ion migration of the electrolyte and excellent in the ability to impregnate the electrolyte may be used. For example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, it may be a non-woven fabric or a woven fabric. For example, a woundable separator such as polyethylene or polypropylene may be used for a lithium ion battery, and a separator having excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A polymer resin, a filler, and a solvent are mixed to prepare a separator composition. The separator composition may be directly coated and dried on an electrode to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled off from the support may be laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. In addition, the electrolyte may be a solid. For example, boron oxide, lithium oxynitride, etc. may be used, but the present invention is not limited thereto, and any solid electrolyte may be used as long as it can be used as a solid electrolyte in the art. The solid electrolyte may be formed on the negative electrode by a method such as sputtering.

For example, an organic electrolyte may be prepared. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , Benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethylsulfoxide , Dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x,y are natural numbers), LiCl, LiI, or a mixture thereof.

As shown in FIG. 4, the lithium battery 1 includes a positive electrode 3, a negative electrode 2, and a separator 4. The positive electrode 3, the negative electrode 2 and the separator 4 described above are wound or folded to be accommodated in the battery case 5. Subsequently, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium battery 1. The battery case may have a cylindrical shape, a square shape, or a thin film shape. For example, the lithium battery may be a large thin film type battery. The lithium battery may be a lithium ion battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the resulting product is accommodated in a pouch and sealed to complete a lithium ion polymer battery.

In addition, a plurality of battery structures are stacked to form a battery pack, and the battery pack can be used in all devices requiring high capacity and high output. For example, it can be used for laptop computers, smart phones, electric vehicles, and the like.

In addition, since the lithium battery has excellent life characteristics and high rate characteristics, it can be used in an electric vehicle (EV). For example, it can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in a field requiring a large amount of power storage. For example, it can be used for electric bicycles, power tools, and the like.

The present invention will be described in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

(Preparation of nickel-based transition metal oxide)

Preparation Example 1: one body NCM

Nickel precursor, NiSO _4, CoSO ₄ cobalt precursor and manganese precursor of MnSO ₄ 0.5: 0.2 was added to the water in a molar ratio of 0.3 nickel cobalt manganese hydroxide precursor solution was prepared. While stirring the aqueous solution, an aqueous sodium hydroxide solution was slowly added dropwise thereto, and the reaction mixture was stirred for 5 hours to neutralize the precursor aqueous solution to precipitate nickel cobalt manganese hydroxide Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ . The precipitate was filtered and washed with water, and the resulting product was dried in an air atmosphere at 80° C. to prepare Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ powder having an average particle diameter of about 6 μm.

The Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ powder was heat-treated at 600° C. for 1 hour in an atmospheric atmosphere to obtain a transition metal oxide having a shape in which moisture was removed and lithium could easily penetrate.

The transition metal oxide and the lithium precursor Li ₂ CO ₃ were prepared in a molar ratio of 1: 0.525. The weight ratio of lithium to each of the transition metals nickel, cobalt, and manganese was about 1.05.

After mixing the prepared precursors in a mortar, a positive electrode active material was prepared by placing it in a furnace and performing secondary heat treatment at 1040°C for 10 hours while flowing O ₂ .

The positive electrode active material obtained according to the above manufacturing method was Li[Ni _0.5 Co _0.2 Mn _0.3 ]O ₂ , the average particle diameter of the primary particles in the form of one body particles of the positive electrode active material was 4 μm, and the average particle diameter of the secondary particles was 6 The state of small-diameter particles of µm was shown.

The average particle diameter of the primary particles of the positive electrode active material was measured through SEM (FEI sirion), and the average particle diameter of the secondary particles was measured through a particle size analyzer (Beckman Coulter LS13 320).

Preparation Example 2: Ni-doped LCO

It was prepared by doping with Ni during the production of the existing LCO. As the Ni source, Ni(OH) ₂ was used. Li ₂ CO ₃ , Co ₃ O ₄ , and Ni(OH) ₂ were mixed and heat treated. The heat treatment temperature was between 1000 and 1100°C.

In the Ni-doped LCO prepared above, the Ni content was 5 mol% based on the total number of moles of Ni and Co.

Comparative Preparation Example 1: Commercial 523 NCM

Li[Ni _0.5 Co _0.2 Mn _0.3 ]O ₂ having an average particle diameter of 6 μm of secondary particles was used as a positive electrode active material.

Comparative Preparation Example 2: Commercial LCO

LiCoO ₂ having an average secondary particle diameter of 16 μm was used as a positive electrode active material.

(Production of positive electrode, negative electrode and lithium battery (full cell))

Comparative Example 1: Positive electrode (one body NCM alone) + negative electrode (graphite:SiOx=90:10)

The positive electrode active material powder synthesized in Preparation Example 1 and the carbon conductive agent (Super P) were uniformly mixed in a weight ratio of 97:1.5. A PVDF (polyvinylidene fluoride) binder solution was added to the mixture to prepare an active material slurry in a weight ratio of active material: carbon conductive agent: binder = 97:1.5:1.5. The slurry was coated on an aluminum current collector having a thickness of 12 μm using a thick film coater so that the loading level was 40 mg/cm ² , dried at 120° C. for 1 hour or more, and then rolled to give a mixture density of 3.7 g/cc. A positive electrode was prepared.

(Cathode manufacturing)

A 1:1 weight ratio of SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) to a mixture of negative electrode active material graphite powder (Japan carbon) and SiOx (0<x<2) (ShinEtsu) in a weight ratio of 90:10 The mixture was mixed at a weight ratio of 98:2 to prepare a negative active material slurry.

The prepared negative active material slurry was coated on a copper foil current collector having a thickness of 8 μm at a level of 16 mg/cm ² . The coated electrode plate was dried at 100° C. for 1 hour or more, and then rolled to prepare a negative electrode having a mixture density of 1.6 g/cc.

(Battery assembly)

The positive and negative electrodes are used, a polyethylene separator (STAR 20, Asahi) is used as a separator, and EC (ethylene carbonate): EMC (ethylmethyl carbonate): DMC (dimethyl carbonate:) (3:3 :4 volume ratio) A lithium battery (full cell) was prepared using 1.15M LiPF ₆ dissolved in a mixed solvent.

Example 1: positive electrode (one body NCM + Ni-doped LCO) + negative electrode (graphite: SiOx = 90:10)

As a positive electrode active material, instead of the positive electrode active material powder synthesized in Preparation Example 1, the positive electrode active material powder synthesized in Preparation Example 1 (one body NCM) and the positive electrode active material powder synthesized in Preparation Example 2 (Ni-doped LCO) in a weight ratio of 10:90 A lithium battery (full cell) having the same capacity was manufactured in the same manner as in Comparative Example 1, except that the mixed mixture was used.

Example 2: positive electrode (one body NCM + Ni-doped LCO) + negative electrode (graphite: SiOx = 90:10)

As a positive electrode active material, instead of the positive electrode active material powder synthesized in Preparation Example 1, the positive electrode active material powder synthesized in Preparation Example 1 (one body NCM) and the positive electrode active material powder synthesized in Preparation Example 2 (Ni doped LCO) in a weight ratio of 20:80 A lithium battery (full cell) having the same capacity was manufactured in the same manner as in Comparative Example 1, except that the mixed mixture was used.

Example 3: positive electrode (one body NCM + Ni-doped LCO) + negative electrode (graphite: SiOx = 90:10)

As a positive electrode active material, instead of the positive electrode active material powder synthesized in Preparation Example 1, the positive electrode active material powder synthesized in Preparation Example 1 (one body NCM) and the positive electrode active material powder synthesized in Preparation Example 2 (Ni doped LCO) in a weight ratio of 30:70 A lithium battery (full cell) having the same capacity was manufactured in the same manner as in Comparative Example 1, except that the mixed mixture was used.

Comparative Example 2: Positive electrode (one body NCM alone) + negative electrode (graphite:SiOx=80:20)

The same capacity as in Comparative Example 1 was used except that the mixing weight ratio of the negative electrode active material, graphite powder (Japan carbon) and SiOx (0<x<2) (ShinEtsu) was changed from 90:10 to 80:20. A lithium battery (full cell) was prepared.

Comparative Example 3: Positive electrode (commercial NCM alone) + negative electrode (graphite:SiOx=90:10)

A lithium battery (full cell) of the same capacity was used in the same manner as in Comparative Example 1, except that the positive electrode active material (commercial NCM) according to Comparative Preparation Example 1 was used instead of the positive electrode active material (one body NCM) prepared in Preparation Example 1. ) Was prepared.

Comparative Example 4: Positive electrode (only commercial LCO) + negative electrode (graphite:SiOx=90:10)

A lithium battery (full cell) of the same capacity was used in the same manner as in Comparative Example 1, except that the positive electrode active material (commercial LCO) according to Comparative Preparation Example 1 was used instead of the positive electrode active material (one body NCM) prepared in Preparation Example 1. ) Was prepared.

Comparative Example 5: Positive electrode (one body NCM alone) + negative electrode (graphite:SiOx=97:03)

Same capacity as in Comparative Example 1, except that the mixing weight ratio of graphite powder (Japan carbon) and SiOx (0<x<2) (ShinEtsu), which is an anode active material, was changed from 90:10 to 97:3. A lithium battery (full cell) was prepared.

Comparative Example 6: Positive electrode (one body NCM alone) + negative electrode (graphite:SiOx=70:30)

The same capacity as in Comparative Example 1 was used except that the mixing weight ratio of the negative electrode active material, graphite powder (Japan carbon) and SiOx (0<x<2) (ShinEtsu) was changed from 90:10 to 70:30. A lithium battery (full cell) was prepared.

Evaluation Example 1: SEM experiment

SEM images of the positive electrode active material prepared in Preparation Example 1 and the positive electrode active material particles prepared in Comparative Preparation Example 1 were measured. The SEM measurement device used the model name (Sirion) of FEI (USA).

1 is a scanning electron microscope (SEM) photograph of the positive electrode active material prepared in Preparation Example 1.

2 is a SEM photograph of the positive electrode active material prepared in Comparative Preparation Example 1.

The positive electrode active material according to Preparation Example 1 shown in FIG. 1 shows that the average particle diameter of the primary particles increases as compared to the positive electrode active material of Comparative Preparation Example 1 of FIG. 2.

The lithium transition metal oxide, which is the positive electrode active material of Comparative Preparation Example 1, has primary particles of about 1 μm, and these primary particles are gathered to form secondary particles.

Evaluation Example 2: Measurement of pH and residual lithium

The pH of the positive electrode active material prepared in Preparation Example 1 and Comparative Preparation Example 1 was measured, and the results are shown in Table 1 below. The pH evaluation was measured using a pH meter [eutech, pH 6000] after stirring 2 g of a positive electrode active material in 100 g of pure water for 10 minutes.

The amount of lithium remaining in the positive electrode active material prepared in Preparation Example 1 and Comparative Preparation Example 1 was measured and shown in Table 1. The residual lithium evaluation was evaluated by a titration method, and the positive electrode active material powder was dissolved in water and then titrated with hydrochloric acid to calculate the contents of LiOH and Li ₂ CO ₃ contained in the positive electrode active material powder, from which LiOH remaining on the positive electrode active material surface or The content of Li ₂ CO ₃ was calculated.

Meanwhile, GC-MS [gas chromatograph-mass spectrometer, Agilent 7000] analysis was performed to check the content of lithium carbonate in the positive electrode active material prepared in Preparation Example 1 and Comparative Preparation Example 1, and the results are shown in Table 1 below. Done.

division pH Residual lithium
(weight%) GC-MS analysis
Content of lithium carbonate
(weight%) LiOH Li ₂ CO ₃ Comparative Production Example 1 11.1 0.086 0.135 0.09 Manufacturing Example 1 10.3 0.02 0.085 0.03

Referring to Table 1, it can be seen that the positive electrode active material of Preparation Example 1 has a small amount of the residual lithium compound present on the surface of the positive electrode active material compared to the positive electrode active material of Comparative Preparation Example 1. This decrease in the amount of residual lithium was also confirmed by a decrease in the pH of the surface of the active material, and the decrease in the pH of the surface of the active material improves the stability of the slurry when manufacturing the positive electrode slurry, and problems such as protrusions and drag on the electrode plate that may occur during coating Can be prevented.

Evaluation Example 3: DSC experiment

The thermal stability of the positive electrode active material obtained according to Preparation Example 1 and Comparative Preparation Example 1 was analyzed using a differential scanning calorimeter, and the results are shown in FIG. 3.

Referring to FIG. 3, the positive electrode active material of Preparation Example 1 exhibits a broad peak as the onset point temperature increases and the main peak calorific value decreases compared to the commercial positive electrode active material of Comparative Preparation Example 1. From this, it was found that the thermal safety of the positive electrode active material of Preparation Example 1 is more excellent.

Evaluation Example 4: Measurement of the mixture density of the positive electrode

After rolling the positive electrode active material layer included in the same positive electrode used in the full cells prepared in Examples 1 to 3 and Comparative Examples 1 to 6, cut it into a size of 30 mm X 30 mm, and then measure the thickness and weight. The density of the mixture was determined. The mixture density is shown in Table 1 below.

As shown in Table 1 below, the positive electrode of Example 1 including the positive electrode active material prepared in Preparation Example 1 and lithium cobalt oxide at the same time has a mixture density compared to Comparative Example 1 including the positive electrode active material prepared in Comparative Preparation Example 1. It was high.

Evaluation Example 5: Evaluation of charge/discharge characteristics of a lithium battery half cell

A half cell was manufactured in the same manner as a full cell except that lithium metal was used as a counter electrode for the same positive and negative electrodes as those used for the full cells prepared in Examples 1 to 3 and Comparative Examples 1 to 6.

The positive electrode was charged at a constant current with a current of 0.1 C at 25° C. until the voltage reached 4.3 V (vs. Li), and charged at a constant voltage until the current reached 0.01 C while maintaining 4.3 V. Subsequently, at the time of discharging, it was discharged at a constant current of 0.1 C until the voltage reached 3.0V (vs. Li). The initial charging and discharging capacity was measured from the charging capacity and charging capacity obtained in the charging and discharging.

The negative electrode was charged at a constant current at a current of 0.1 C at 25° C. until the voltage reached 0.01 V (vs. Li), and charged at a constant voltage until the current reached 0.01 C while maintaining 0.01 V. Then, at the time of discharging, it was discharged with a constant current of 0.1 C until the voltage reached 1.5 V (vs. Li). The initial charging and discharging capacity was measured from the charging capacity and charging capacity obtained in the charging and discharging.

The results of the charge/discharge experiment are shown in Table 2 below. The initial charge/discharge efficiency is expressed by Equation 1 below.

<Equation 1>

Initial charge/discharge efficiency[%]=[discharge capacity/charge capacity]×100

Initial charge/discharge efficiency [%] Positive electrode mixture density
[g/cc] anode cathode Comparative Example 1 85 85 3.4 Example 1 91.2 85 3.95 Example 2 90.5 85 3.95 Example 3 89.7 85 3.9 Comparative Example 2 85 81 3.4 Comparative Example 3 89 85 3.3 Comparative Example 4 95 85 3.95 Comparative Example 5 85 88 3.4 Comparative Example 6 85 79 3.4

As shown in Table 2, the anodes of Examples 1 to 3 had higher initial charge/discharge efficiency than the cathode. In addition, the initial charge/discharge efficiency of the positive electrodes of Examples 1 to 5 was 91.2% or less. In addition, the mixture density of the positive electrodes of Examples 1 to 5 was 3.5 g/cc or more.

In addition, although not described in the above table, the initial charging capacity of the positive electrodes of Examples 1 to 3 was 200 mAh/g or more.

Evaluation Example 6: Evaluation of charge/discharge characteristics of a lithium battery full cell

When the full cells prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were charged at a constant current with a current of 0.2C at 25°C until the voltage reached 4.3V, and the current became 0.01C while maintaining 4.3V To a constant voltage charge. Then, at the time of discharging, it was discharged with a constant current of 0.2C until the voltage reached 2.75V.

Subsequently, constant current charging was performed with a current of 0.5C until the voltage reached 4.3V, and constant voltage charging was performed until the current reached 0.01C while maintaining 4.3V. Then, at the time of discharging, discharge was performed at a constant current of 0.5C until the voltage reached 2.75V (ideal formation step).

The lithium battery that had undergone the formation step was charged at a constant current at 25° C. at a current of 1.0 C until the voltage reached 4.3 V, and while maintaining 4.3 V, the lithium battery was charged at a constant voltage until the current reached 0.01 C. Subsequently, the cycle of discharging with a constant current of 1.0 C was repeated 100 times until the voltage reached 2.75 V during discharge.

The results of the charge/discharge experiment are shown in Table 3 below. The initial discharge capacity is the discharge capacity in the first cycle, and the capacity retention rate is expressed by Equation 2 below.

<Equation 2>

Capacity retention rate [%] = [Discharge capacity at 100 ^th cycle/1 Discharge capacity at ^st cycle] × 100

In 1 ^th cycle
Discharge capacity [mAh] At 100 ^th cycle
Capacity retention rate [%] Comparative Example 1 1335 93 Example 2 1420 95 Example 3 1448 96 Example 4 1485 95 Comparative Example 2 1341 93 Comparative Example 3 1375 91 Comparative Example 4 1393 93 Comparative Example 5 1339 93 Comparative Example 6 1337 89

As shown in Table 3, the lithium batteries of Examples 1 to 3 have improved discharge capacity and life characteristics compared to the lithium batteries of Comparative Examples 1 to 6.

Claims (15)

anode; cathode; And an electrolyte disposed between the positive electrode and the negative electrode,
The positive electrode comprises a nickel-based lithium transition metal oxide and a lithium cobalt oxide having an average particle diameter of 2 μm or more of the primary particles,
The negative electrode comprises graphite and a silicon-based compound,
The lithium battery, wherein the content of the silicon-based compound is 5% to less than 20% by weight based on the total weight of graphite and the silicon-based compound. The lithium battery according to claim 1, wherein the initial charge/discharge efficiency of the positive electrode is equal to or higher than the initial charge/discharge efficiency of the negative electrode. The lithium battery according to claim 1, wherein the silicon-based compound is silicon, a silicon alloy, or a silicon oxide. The lithium battery according to claim 1, wherein the silicon-based compound is a silicon oxide represented by the following Formula 1:
<Formula 1>
SiO _x
In the above formula, 0<x<2.0. The lithium battery according to claim 1, wherein the nickel-based lithium transition metal oxide is a compound represented by the following formula (2):
<Formula 2>
Li _x Co _a Ni _b M _c O _2+α
In the above formula, 0.9<x<1.5, 0<a<0.5, 0<b<1, 0<c<1, -0.1≤α≤0.1,
M is at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Mn, Cr, Fe, Mg, Sr, V, and rare earth elements to be. The lithium battery according to claim 1, wherein the nickel-based lithium transition metal oxide is a compound represented by the following formula (3):
<Formula 3>
Li _x Co _a Ni _b Mn _c O _2+α
In the above formula, 0.9<x<1.1, 0<a<0.5, 0.4<b<1, 0<c<0.5, -0.1≦α≦0.1. The lithium battery according to claim 1, wherein the on-set point temperature is 250 to 270°C in the differential scanning calorimeter analysis of the nickel-based lithium transition metal oxide. The lithium battery according to claim 1, wherein the content of the lithium cobalt oxide is 65% by weight or more based on the total weight of the nickel-based lithium transition metal oxide and the lithium cobalt oxide. The lithium battery according to claim 1, wherein the content of the lithium cobalt oxide is 90 to 70% by weight based on the total weight of the nickel-based lithium transition metal oxide and the lithium cobalt oxide. The lithium battery according to claim 1, wherein at least a portion of the lithium cobalt oxide is doped with nickel. The lithium battery according to claim 1, wherein the content of the nickel is 20 mol% or less with respect to the total mol number of nickel and cobalt. The lithium battery according to claim 1, wherein the positive electrode has an initial charge/discharge efficiency of 91.5% or less. The lithium battery according to claim 1, wherein the positive electrode has a mixture density of 3.5 g/cc or more. The lithium battery according to claim 1, wherein the negative electrode has an initial charge/discharge efficiency of 88.0% or less. The lithium battery according to claim 1, wherein the positive electrode has an initial charging capacity of 200 mAh/g or more.

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