JP4795019B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to improvement of a non-aqueous electrolyte.

In recent years, research on secondary batteries including non-aqueous electrolytes (non-aqueous electrolyte secondary batteries), in particular, lithium ion secondary batteries having a high voltage and a high energy density has been actively conducted. Currently, most of the commercially available lithium secondary batteries use LiCoO ₂ exhibiting a high charge / discharge voltage as a positive electrode active material. In addition, a nonaqueous solvent in which a solute is dissolved is generally used for the nonaqueous electrolyte. As the non-aqueous solvent, a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester or the like is used. As the solute, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like is used.

There is a strong demand for higher capacity of non-aqueous electrolyte secondary batteries, and research and development on a positive electrode active material with higher capacity in place of LiCoO ₂ has been actively conducted. Among them, research on nickel-containing lithium composite oxide (for example, LiNiO ₂ ) whose main component is nickel has been vigorously conducted, and some have already been commercialized.

High reliability and long life of non-aqueous electrolyte secondary batteries are also desired. However, a battery using LiNiO ₂ generally has lower cycle characteristics and thermal safety than a battery using LiCoO ₂ . Therefore, the battery using LiNiO ₂ has not yet occupied the market.

Therefore, improvement of nickel-containing lithium composite oxide is being actively carried out. For example, Li _{a Mb} Ni _c Co _d O _e (element M is at least one selected from the group consisting of Al, Mn, Sn, In, Fe, V, Cu, Mg, Ti, Zn and Mo, 0 < a <1.3, 0.02 ≦ b ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, b + c + d = 1) is proposed. . It has been reported that this active material is less likely to change the crystal structure, and therefore can be increased in capacity and improved in thermal stability (see Patent Document 1).

In addition, attempts have been made to mix various additives into the positive electrode active material, the negative electrode active material, and the nonaqueous electrolyte. For example, it has been proposed to add a fluorine atom-containing aromatic compound to a non-aqueous electrolyte (see Patent Documents 2 and 3). The purpose of Patent Document 2 is to improve charge / discharge cycle characteristics. The fluorine atom-containing aromatic compound is adsorbed on the negative electrode surface or reacts with the negative electrode surface to form a film. Therefore, it is reported that a side reaction between the nonaqueous electrolyte and the negative electrode active material is suppressed. Moreover, in patent document 3, the fluorine atom containing aromatic compound is used in order to suppress the gas generation at the time of continuous charge.
Japanese Patent Laid-Open No. 5-242891 JP 2003-132950 A JP 2004-139963 A

As described above, the nickel-containing lithium composite oxide has been improved, but at present, sufficient cycle characteristics have not been obtained. Moreover, even if a non-aqueous electrolyte contains a fluorine atom-containing aromatic compound, it is still difficult to improve cycle characteristics. In particular, in a high temperature environment, it has been found that the side reaction between the non-aqueous electrolyte and the positive electrode active material becomes intense and the cycle characteristics are greatly deteriorated.
Patent Document 2 intends to suppress a side reaction between a nonaqueous electrolyte and a negative electrode active material. Therefore, no effective proposal has been made regarding the suppression of side reactions between the nonaqueous electrolyte and the positive electrode active material when the charge / discharge cycle is repeated at a high temperature.
Patent Document 3 intends to suppress gas generation during continuous charging (static trickle charging) of a battery whose positive electrode active material is general LiCoO ₂ . Therefore, no effective proposal has been made regarding the suppression of side reactions between the nonaqueous electrolyte and the positive electrode active material when a dynamic charge / discharge cycle is repeated at a high temperature.

  The present invention has been made in view of the above, and in the case of using a nickel-containing lithium composite oxide as a positive electrode active material, a high capacity type non-aqueous electrolyte exhibiting good charge / discharge cycle characteristics even in a high temperature environment A secondary battery is provided.

  The present invention includes a positive electrode including a nickel-containing lithium composite oxide as a positive electrode active material, a negative electrode capable of charge / discharge, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous solvent in which a solute is dissolved. The present invention relates to a non-aqueous electrolyte secondary battery including a water electrolyte, wherein the non-aqueous electrolyte includes a fluorine atom-containing aromatic compound.

Nickel-containing lithium composite oxide is represented by the general formula (1): is represented by _{LiNi x M 1-xy L y} O 2, element M is at least one selected from the group consisting of Co and Mn, the element L Was selected from the group consisting of Al, Sr, Y, Zr, Ta, Mg, Ti, Zn, B, Ca, Cr, Si, Ga, Sn, P, V, Sb, Nb, Mo, W and Fe Preferably, x and y satisfy at least 0.1 ≦ x ≦ 1 and 0 ≦ y ≦ 0.1.

  The fluorine atom-containing aromatic compound has the general formula (2):

It is preferable to be represented by Here, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently a fluorine atom or a hydrogen atom, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and At least one of R ₆ is a fluorine atom.

The amount of the fluorine atom-containing aromatic compound contained in the non-aqueous electrolyte is 1 to 30 parts by weight per 100 parts by weight of the non-aqueous solvent.
Non-aqueous electrolyte further comprises at least one of including selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate. The amount of at least one selected from the group consisting of vinylene carbonate and vinyl ethylene carbonate contained in the nonaqueous electrolyte is 0.5 to 10 parts by weight per 100 parts by weight of the nonaqueous solvent.

  As a result of repeated studies, the inventors of the present invention have found that the fluorine atom-containing aromatic compound acts particularly effectively on the positive electrode active material composed of the nickel-containing lithium composite oxide, and the non-aqueous electrolyte and the positive electrode active material It has been found that side reactions are significantly suppressed. The reason is considered as follows.

  By dissolving Ni in the crystal structure of the positive electrode active material, NiO that is a metal oxide is generated on the surface of the positive electrode active material. Since NiO is a basic oxide, the electron density on the oxygen atoms of NiO is high. On the other hand, the aromatic ring of the fluorine atom-containing aromatic compound has a positive quadrupole moment due to the strong electron attractive force of fluorine, and the electron density on the aromatic ring is low. For this reason, the fluorine atom-containing aromatic compound in the non-aqueous electrolyte is attracted to the oxygen atoms of NiO and adsorbs on the surface of the positive electrode active material to form a film. It is considered that this coating suppresses the side reaction between the nonaqueous electrolyte and the positive electrode active material even under a high temperature environment, and improves the cycle characteristics.

  According to the present invention, even when nickel-containing lithium composite oxide is used as a positive electrode active material for increasing the capacity, side reactions between the nonaqueous electrolyte and the positive electrode active material in a high temperature environment are suppressed, and cycle characteristics are deteriorated. Is avoided. Therefore, a non-aqueous electrolyte secondary battery having good characteristics can be obtained.

The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode including a nickel-containing lithium composite oxide as a positive electrode active material. When nickel-containing lithium composite oxide is used, it is possible to obtain an inexpensive and high-capacity battery as compared with the case of using LiCoO ₂ . However, if only a nickel-containing lithium composite oxide is used, it is difficult to obtain sufficient cycle characteristics even if a high capacity is obtained. Therefore, in the present invention, the non-aqueous electrolyte contains a fluorine atom-containing aromatic compound.

Nickel-containing lithium composite oxide is represented by the general formula (1): It is desirable represented by _{LiNi x M 1-xy L y} O 2. Here, from the viewpoint of stabilizing the crystal structure and obtaining good battery characteristics, the element M is at least one selected from the group consisting of Co and Mn, and the element L is Al, Sr, Y, Desirably, at least one selected from the group consisting of Zr, Ta, Mg, Ti, Zn, B, Ca, Cr, Si, Ga, Sn, P, V, Sb, Nb, Mo, W, and Fe. . The element M has a function of stabilizing the crystal structure without significantly reducing the capacity, and the element L has a function of stabilizing the crystal structure and improving the electron donating property of NiO on the surface of the positive electrode active material. . A positive electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

Among the elements L, Al, Sr, Y, Zr and Ta are particularly preferable. Metal oxides generated from these elements (for example, Al ₂ O ₃ and SrO) have a large effect of increasing the electron donating property of NiO on the surface of the positive electrode active material, and a good quality protective film is formed on the surface of the positive electrode. Therefore, in order to obtain particularly good cycle characteristics, it is desirable that the element L is at least one selected from the group consisting of Al, Sr, Y, Zr and Ta.

  From the viewpoint of obtaining the effect of the element M and maintaining a high capacity, x in the general formula (1) desirably satisfies 0.1 ≦ x ≦ 1, and satisfies 0.3 ≦ x ≦ 0.9. It is more desirable that 0.7 ≦ x ≦ 0.9 is satisfied.

  The element L is not essential, but from the viewpoint of obtaining the effect of the element L and maintaining a high capacity, y in the general formula (1) desirably satisfies 0 <y ≦ 0.1, and 0.02 It is further desirable to satisfy ≦ y ≦ 0.08, and it is particularly desirable to satisfy 0.02 ≦ y ≦ 0.06. When y exceeds 0.1, the electron donating property of NiO is excessively activated, and the cycle characteristics at high temperature are slightly lowered.

  The nonaqueous electrolyte secondary battery of the present invention includes a negative electrode that can be charged and discharged. The negative electrode capable of charge / discharge includes a material capable of inserting and extracting lithium or lithium metal as a negative electrode active material. As a material capable of inserting and extracting lithium, a metal, a carbon material, an oxide, a nitride, a tin compound, a silicide, or the like can be used. Metals include simple metals, alloys, metal fibers and the like. Examples of the carbon material include graphites, non-graphitizable carbon, carbon blacks, and carbon fibers. Graphite includes natural graphite (such as flake graphite) and artificial graphite. Carbon blacks include acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and the like. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  Each of the positive electrode and the negative electrode includes the positive electrode active material and the negative electrode active material as essential components, and includes a binder, a conductive material, a thickener, and the like as optional components. Examples of the binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Etc. are used. As the conductive material, for example, graphites, carbon blacks, carbon fibers, metal fibers and the like are used.

  The positive electrode is produced, for example, by mixing a positive electrode mixture composed of a positive electrode active material and an optional component with a liquid component to prepare a positive electrode mixture slurry, applying the obtained slurry to a positive electrode current collector, and drying. Similarly, the negative electrode is prepared by mixing a negative electrode mixture composed of a negative electrode active material and an optional component with a liquid component to prepare a negative electrode mixture slurry, applying the obtained slurry to a negative electrode current collector, and drying the mixture. .

  For the positive electrode current collector, for example, a sheet (foil) made of stainless steel, aluminum, titanium, or the like is used. For the negative electrode current collector, for example, a sheet (foil) made of stainless steel, nickel, copper, or the like is used. Although the thickness of these electrical power collectors is not specifically limited, 1-500 micrometers is suitable.

The non-aqueous electrolyte secondary battery of the present invention includes a non-aqueous electrolyte including a non-aqueous solvent in which a solute is dissolved, and the non-aqueous electrolyte includes a fluorine atom-containing aromatic compound. Although the solute concentration in the nonaqueous electrolyte is not particularly limited, for example, 0.5 to 1.5 mol / L is preferable.
Here, the fluorine atom-containing aromatic compound includes the general formula (2):

It is preferable to use the fluorine atom containing aromatic compound represented by these. R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently a fluorine atom or a hydrogen atom, but R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ At least one of is a fluorine atom. In the compound represented by the general formula (2), since a fluorine atom having a strong electron withdrawing force is directly bonded to the aromatic ring, the electron density of the aromatic ring tends to be low. Therefore, the aromatic ring is easily attracted to the surface of the positive electrode active material, and a strong film can be formed on the surface of the positive electrode. A fluorine atom containing aromatic compound may be used individually by 1 type, and may be used in combination of 2 or more type.

  In general formula (2), the number of fluorine atoms bonded to the benzene ring may be any one of 1 to 6, but is preferably smaller. When the number of fluorine atoms increases, the fluorine atom-containing aromatic compound may be excessively adsorbed on the surface of the positive electrode and the charge / discharge reaction may be inhibited. Accordingly, it is most preferable to use fluorobenzene (FB) as the fluorine atom-containing aromatic compound. In the case of FB, since there is one fluorine atom directly bonded to the aromatic ring, the electron density of the aromatic ring becomes moderately low. Therefore, FB is easily adsorbed on the surface of the positive electrode and is not excessively adsorbed on the surface of the positive electrode.

The amount of fluorine-containing aromatic compound contained in the non-aqueous electrolyte, a non-aqueous solvent per 100 parts by weight, 1 to 30 parts by weight, good preferable 5 to 20 parts by weight. When the amount of the fluorine atom-containing aromatic compound is less than 1 part by weight, the ability to form a coating on the surface of the positive electrode is reduced, and when it exceeds 30 parts by weight, the coating becomes too thick and the charge / discharge reaction may be inhibited. .

  As the non-aqueous solvent, for example, a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester or the like is used. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). A non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

Solutes to be dissolved in the non-aqueous solvent include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, borates, imide salts, and the like can be used. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ') and bis (2,3-naphthalenedioleate (2-)-O, O') boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate Etc. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. A solute may be used individually by 1 type, and may be used in combination of 2 or more type.

  The non-aqueous electrolyte may further contain a cyclic carbonate having at least one carbon-carbon unsaturated bond. Examples of the cyclic carbonate having at least one carbon-carbon unsaturated bond include vinylene carbonate (VC), 3-methyl vinylene carbonate, 3,4-dimethyl vinylene carbonate, 3-ethyl vinylene carbonate, 3,4-diethyl. Examples include vinylene carbonate, 3-propyl vinylene carbonate, 3,4-dipropyl vinylene carbonate, 3-phenyl vinylene carbonate, 3,4-diphenyl vinylene carbonate, vinyl ethylene carbonate (VEC), and divinyl ethylene carbonate. These may be used alone or in combination of two or more. These also have a function of forming a film on the electrode surface and suppressing side reactions.

In the present invention, carbon - Among these carbon unsaturated bonds having at least one cyclic ester carbonate, Ru using at least one selected especially from vinylene carbonate (VC) and the group consisting of vinyl ethylene carbonate (VEC). Although VC and VEC are known to decompose on the negative electrode surface to form a film, it is considered that a thin film is also formed on the positive electrode surface. When the positive electrode includes a nickel-containing lithium composite oxide, a hybrid coating (copolymer) including a unit derived from a fluorine atom-containing aromatic compound and a unit derived from VC or VEC is formed on the surface of the positive electrode. This hybrid film has a function of greatly improving the adhesion between the positive electrode and the separator.

  The coating derived from the fluorine atom-containing aromatic compound is strong and hard and difficult to peel off from the surface of the positive electrode, but it is poor in flexibility. Therefore, the adhesiveness between the positive electrode and the separator tends to decrease. On the other hand, a hybrid coating (copolymer) containing units derived from VC or VEC has flexibility because it has a low glass transition temperature and a low elastic modulus from a low temperature to a high temperature region. Therefore, the adhesion between the positive electrode and the separator is improved. Thereby, when a battery is exposed to overcharge or high temperature, and a separator shuts down, the shrinkage | contraction of a separator can be suppressed and the internal short circuit which a negative electrode and a positive electrode contact can be prevented. The shutdown of the separator is a phenomenon that the pores of the separator are blocked when the battery is exposed to a high temperature.

  The amount of the cyclic carbonate having at least one carbon-carbon unsaturated bond contained in the nonaqueous electrolyte is preferably 0.5 to 10 parts by weight, and 0.5 to 7 parts by weight per 100 parts by weight of the nonaqueous solvent. Part is particularly preferred. If the amount of the cyclic carbonate having at least one carbon-carbon unsaturated bond is less than 0.5 parts by weight, the effect of improving the adhesion between the positive electrode and the separator is reduced. It may become too thick and the charge / discharge reaction may be inhibited.

  The non-aqueous solvent can contain a small amount of an additive that decomposes during overcharge to form a film on the electrode and inactivates the battery. As such an additive, a benzene derivative composed of a phenyl group and a cyclic compound group adjacent to the phenyl group is preferably used. Here, as the cyclic compound group, a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, a phenoxy group, and the like are preferable. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether and the like. These may be used alone or in combination of two or more. However, it is preferable that the content rate of a benzene derivative is 10 volume% or less of the whole non-aqueous solvent.

  As the separator interposed between the positive electrode and the negative electrode, a microporous thin film, a woven fabric, a non-woven fabric, or the like having both high ion permeability, predetermined mechanical strength, and insulation is used. As a material of the separator, for example, polyolefin such as polypropylene and polyethylene is preferable, but glass fiber or the like may be used. In particular, a polyolefin microporous thin film having a shutdown function is preferably used. The thickness of the separator is generally 10 to 300 μm.

EXAMPLES Next, although this invention is demonstrated concretely based on an Example, a following example does not limit this invention.
<< Reference Example 1 >>
(I) Preparation of non-aqueous electrolyte LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio 1: 4) at a concentration of 1.0 mol / L. To the obtained solution, 5 parts by weight of fluorobenzene (FB) was added per 100 parts by weight of the non-aqueous solvent to obtain a non-aqueous electrolyte.

(Ii) Production of positive electrode A positive electrode mixture in which 85 parts by weight of LiNi _0.8 Co _0.2 O ₂ powder as a positive electrode active material, 10 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder was mixed. Then, the mixture was dispersed in dehydrated N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. This slurry was applied to both surfaces of a positive electrode current collector made of an aluminum foil, dried and rolled to obtain a positive electrode.

(Iii) Production of Negative Electrode A negative electrode mixture obtained by mixing 75 parts by weight of artificial graphite powder of a negative electrode active material, 20 parts by weight of acetylene black as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder was added to dehydrated NMP. The mixture was dispersed to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a negative electrode current collector made of copper foil, dried and rolled to obtain a negative electrode.

(Iv) Production of Cylindrical Battery A cylindrical battery having a schematic longitudinal section shown in FIG. 1 was produced in the following manner.
The positive electrode 11 and the negative electrode 12 were wound around the separator 13 in a spiral shape to produce an electrode plate group. The electrode plate group was housed in a nickel-plated iron battery case 18. One end of the positive electrode lead 14 made of aluminum was connected to the positive electrode 11, and the other end was connected to the back surface of the sealing plate 19 that was conducted to the positive electrode terminal 20. One end of a nickel negative electrode lead 15 was connected to the negative electrode 12, and the other end was connected to the bottom of the battery case 18. An insulating plate 16 is disposed above the electrode plate group, and an insulating plate 17 is disposed below the electrode plate group. A predetermined nonaqueous electrolyte was poured into the battery case 18, and the opening of the battery case 18 was sealed using the sealing plate 19.

(V) Evaluation of battery The charging / discharging cycle was repeated at 45 degreeC with respect to the obtained battery. Then, the discharge capacity at the third cycle was regarded as 100%, and the ratio of the discharge capacity of the battery after 500 cycles was obtained as a percentage to obtain the capacity maintenance rate. The results are shown in Table 1.

  In the charge / discharge cycle, a constant current / constant voltage charge is performed for 2 hours and 30 minutes under the conditions of a maximum current of 1050 mA and an upper limit voltage of 4.2 V, and after a pause of 10 minutes, a discharge current of 1500 mA and a discharge end voltage of 3.0 V Then, a constant current discharge was performed and a pause for 10 minutes was performed. This cycle was repeated.

<< Comparative Example 1 >>
A battery was prepared in the same manner as in Reference Example 1 except that FB was not included in the nonaqueous electrolyte, and was similarly evaluated. The results are shown in Table 1.

<< Comparative Example 2 >>
A battery similar to that of Reference Example 1 was prepared and evaluated in the same manner except that lithium cobalt oxide (LiCoO ₂ ) was used as the positive electrode active material. The results are shown in Table 1.

<< Comparative Example 3 >>
A battery was prepared in the same manner as in Reference Example 1 except that the same nonaqueous electrolyte as in Comparative Example 1 was used and the same positive electrode active material as in Comparative Example 2 was used. The results are shown in Table 1.
<< Comparative Examples 4-8 >>
A battery similar to that of Reference Example 1 was prepared and evaluated in the same manner except that the same non-aqueous electrolyte as in Comparative Example 1 was used, and the nickel-containing lithium composite oxide having the composition shown in Table 1 was used as the positive electrode active material. . The results are shown in Table 1.

  From Table 1, it can be seen that good cycle characteristics can be obtained only when nickel-containing lithium composite oxide is used as the positive electrode active material and FB is included in the nonaqueous electrolyte. This can be inferred that FB in the non-aqueous electrolyte having a low electron density was adsorbed on the surface of the positive electrode active material containing NiO having a high electron density, and a protective film was formed on the surface of the positive electrode.

<< Reference Example 2 >>
A battery similar to that of Reference Example 1 was prepared and evaluated in the same manner except that a nickel-containing lithium composite oxide having the composition shown in Table 2 was used as the positive electrode active material. The results are shown in Table 2.

From Table 2, the general formula (1): is represented by _{LiNi x M 1-xy L y} O 2, the element M is at least one selected from the group consisting of Co and Mn, the element L is, Al, At least one selected from the group consisting of Sr, Y, Zr, Ta, Mg, Ti, Zn, B, Ca, Cr, Si, Ga, Sn, P, V, Sb, Nb, Mo, W and Fe A combination of a nickel-containing lithium composite oxide in which x and y satisfy 0.1 ≦ x ≦ 1 and 0 ≦ y ≦ 0.1, and a non-aqueous electrolyte containing FB, and a cycle at a high temperature It can be seen that a battery having excellent characteristics can be obtained.

  The x value indicating the Ni content in the positive electrode active material is preferably in the range of 0.1 ≦ x ≦ 0.9, more preferably in the range of 0.3 ≦ x ≦ 0.9, and 0.7 ≦ x It can be seen that a range of ≦ 0.9 is particularly preferable.

  Further, from Table 2, when the element L in the general formula (1) is at least one selected from the group consisting of Al, Sr, Y, Zr and Ta, a battery particularly excellent in high-temperature cycle characteristics is obtained. I understand that

<< Reference Example 3 >>
A battery similar to that of Reference Example 1 was prepared and evaluated in the same manner except that the compounds shown in Table 3 were used as the fluorine atom-containing aromatic compound contained in the nonaqueous electrolyte. The results are shown in Table 3.

  From Table 3, regardless of the type of fluorine atom-containing aromatic compound, a cycle at a high temperature can be achieved by combining a positive electrode active material composed of a nickel-containing lithium composite oxide and a non-aqueous electrolyte containing a fluorine atom-containing aromatic compound. It can be seen that a battery having excellent characteristics can be obtained.

  Among the fluorine atom-containing aromatic compounds, compounds represented by the general formula (2), specifically FB, 1,2-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,3, When 4-tetrafluorobenzene, pentafluorobenzene and hexafluorobenzene were used, the cycle characteristics at high temperature were particularly excellent. In these fluorine atom-containing aromatic compounds, since a fluorine atom having a strong electron attractive force is directly bonded to the aromatic ring, the electron density of the aromatic ring tends to be low. Therefore, it is considered that the amount of the fluorine atom-containing aromatic compound attracted to and adsorbed on the surface of the positive electrode active material increased, and a strong film was formed.

  Further, among the compounds represented by the general formula (2), when FB was used, the cycle characteristics were particularly excellent. In the case of FB, since there is one fluorine atom directly bonded to the aromatic ring, it is considered that the electron density of the aromatic ring is too low to be excessively adsorbed on the positive electrode surface. Therefore, it is considered that good cycle characteristics were obtained because the charge / discharge reaction was not hindered.

<< Reference Example 4 >>
A battery similar to that of Reference Example 1 was prepared and evaluated in the same manner except that the amount (parts by weight) of FB contained in the nonaqueous electrolyte was changed as shown in Table 4 with respect to 100 weights of the nonaqueous solvent. . The results are shown in Table 4.

  From Table 4, it can be seen that when the amount of FB is less than 1 part by weight per 100 parts by weight of the nonaqueous solvent, the effect of improving the cycle characteristics becomes small. In addition, even when the amount of FB exceeds 30 parts by weight, the coating formed on the surface of the positive electrode becomes too thick and the charge / discharge reaction is hindered, so that the effect of improving the cycle characteristics is reduced. . The amount of the fluorine atom-containing aromatic compound is preferably 1 to 30 parts by weight and particularly preferably 5 to 20 parts by weight per 100 parts by weight of the nonaqueous solvent.

Example 1
As the fluorine atom-containing aromatic compound contained in the nonaqueous electrolyte, the compounds shown in Table 5 were used, and further, vinylene carbonate (VC) in an amount (part by weight) described in Table 5 with respect to 100 weights of the nonaqueous solvent, and / or A battery was prepared in the same manner as in Reference Example 1 except that vinyl ethylene carbonate (VEC) was included in the nonaqueous electrolyte, and was evaluated in the same manner. The results are shown in Table 5.

Next, a heat resistance test at 150 ° C. was performed on the battery of Example 1 , and the shrinkage time of the separator was measured. The test method is as follows.
First, the battery was charged with a constant current and a constant voltage for 2 hours and 30 minutes under the conditions of a maximum current of 1050 mA and an upper limit voltage of 4.2 V. Next, the battery in a charged state was heated from 20 ° C. to 150 ° C. at a constant rate of 5 ° C./min, and held at that temperature for 3 hours after reaching 150 ° C. At this time, when the separator is shut down and contraction of the separator occurs, the negative electrode and the positive electrode come into contact (short-circuit), so that the battery voltage rapidly decreases from about 4.2V to about 0V. Therefore, the voltage of the battery being held at 150 ° C. was constantly monitored, and the time from the start of the test until the battery voltage suddenly decreased was measured and used as the contraction time. The results are shown in Table 5.

<< Comparative Example 9 >>
The non-aqueous electrolyte does not contain a fluorine atom-containing aromatic compound, and the amount (parts by weight) of vinylene carbonate (VC) and / or vinyl ethylene carbonate (VEC) shown in Table 5 with respect to 100 weight of the non-aqueous solvent A battery was prepared in the same manner as in Reference Example 1 except that it was included in the water electrolyte, and was evaluated in the same manner as in Example 1 . The results are shown in Table 5.

  From Table 5, it can be seen that the combined use of a fluorine atom-containing aromatic compound and VC and / or VEC not only further improves the cycle characteristics at high temperature, but also greatly improves the heat resistance of the battery. . The heat resistance is greatly improved because the surface of the positive electrode active material made of a nickel-containing lithium composite oxide has a hybrid coating containing a unit derived from a fluorine atom-containing aromatic compound and a unit derived from VC or VEC. This is thought to be due to the formation of That is, the hybrid coating greatly improved the adhesion between the positive electrode and the separator, so that the shrinkage of the separator was suppressed during the shutdown of the separator, the contact (short circuit) between the negative electrode and the positive electrode was prevented, and safety was improved. Conceivable.

  The present invention is applicable to all non-aqueous electrolyte secondary batteries using nickel-containing lithium composite oxide as a positive electrode active material, but particularly when providing a non-aqueous electrolyte secondary battery having excellent life characteristics at high temperatures. Useful. The nonaqueous electrolyte secondary battery of the present invention is useful as a power source for small portable devices, for example.

It is a schematic longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 13 Separator 14 Positive electrode lead 15 Negative electrode lead 16 Upper insulating plate 17 Lower insulating plate 18 Battery case 19 Sealing plate 20 Positive electrode terminal

Claims (5)

A non-aqueous electrolyte comprising a positive electrode including a nickel-containing lithium composite oxide as a positive electrode active material, a negative electrode capable of charge / discharge, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous solvent in which a solute is dissolved And
The nonaqueous electrolyte is seen containing a fluorine atom-containing aromatic compound of the nonaqueous solvent to 30 parts by weight per 100 parts by weight, and the nonaqueous solvent 0.5 to 10 parts by weight per 100 parts by weight, vinylene at least one of including a non-aqueous electrolyte secondary batteries selected from the group consisting of carbonate and vinyl ethylene carbonate. It said nickel-containing lithium composite oxide is represented by the general formula (1): is represented by _{LiNi x M 1-xy L y} O 2,
The element M is at least one selected from the group consisting of Co and Mn,
The element L is selected from the group consisting of Al, Sr, Y, Zr, Ta, Mg, Ti, Zn, B, Ca, Cr, Si, Ga, Sn, P, V, Sb, Nb, Mo, W, and Fe. At least one kind,
The nonaqueous electrolyte secondary battery according to claim 1, wherein x and y satisfy 0.1 ≦ x ≦ 1 and 0 ≦ y ≦ 0.1.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the element L is at least one selected from the group consisting of Al, Sr, Y, Zr, and Ta. The fluorine atom-containing aromatic compound has the general formula (2):

Represented by
R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently a fluorine atom or a hydrogen atom;
The nonaqueous electrolyte secondary battery according to claim 1, wherein at least one of R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ is a fluorine atom.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the fluorine atom-containing aromatic compound is fluorobenzene.

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