JP5235307B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery, and in particular, the addition of a dissimilar metal element in which at least one dissimilar element of zirconium, titanium, aluminum, and magnesium is homogeneously dispersed in lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material The present invention relates to a non-aqueous electrolyte secondary battery using lithium cobalt oxide and having excellent cycle characteristics and a large battery capacity.

  With the rapid spread of portable electronic devices, the required specifications for the batteries used for them are becoming stricter year by year, and in particular, small and thin, high capacity, excellent cycle characteristics, and stable performance are required. Yes. In the field of secondary batteries, lithium non-aqueous electrolyte secondary batteries, which have a higher energy density than other batteries, are attracting attention, and the proportion of lithium non-aqueous electrolyte secondary batteries shows a significant increase in the secondary battery market. ing.

  FIG. 1 is a perspective view showing a conventional cylindrical non-aqueous electrolyte secondary battery cut in the longitudinal direction. The non-aqueous electrolyte secondary battery 10 uses a spiral electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound via a separator 13, and insulating plates 15 and 16 are respectively provided above and below the spiral electrode body 14. Is placed in a steel cylindrical battery outer can 17 also serving as a negative electrode terminal, and the current collecting tab 12a of the negative electrode 12 is welded to the inner bottom of the battery outer can 17 and the positive electrode 11 is collected. The electric tab 11a is welded to the bottom plate portion of the current interrupting sealing body 18 in which the safety device is incorporated, and a predetermined nonaqueous electrolyte is injected from the opening of the battery outer can 17. It is manufactured by sealing the can 17. Such a non-aqueous electrolyte secondary battery has an excellent effect of high battery performance and high battery reliability.

  As a negative electrode active material used in this non-aqueous electrolyte secondary battery, carbonaceous materials such as graphite and amorphous carbon are widely used. The reason is that the carbonaceous material has a discharge potential comparable to that of lithium metal or lithium alloy, but has high safety because dendrites do not grow, and further has excellent initial efficiency and potential flatness. Moreover, it is because it has the outstanding property that density is also high.

  In addition, as the non-aqueous solvent of the non-aqueous electrolyte, carbonates, lactones, ethers, esters and the like are used alone or in combination of two or more, and among these, the dielectric constant is particularly high. Many carbonates which are large and have a high ionic conductivity of the non-aqueous electrolyte are used.

As the cathode active _{material, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNiO 2, LiFeO lithium composite oxide such as ₂ 4V-grade non-aqueous electrolyte of high energy density by combining a negative electrode made of a carbon material It is known that a secondary battery can be obtained. Of these, LiCoO ₂ is often used because various battery characteristics are superior to others. However, since cobalt is expensive and has a small abundance as a resource, in order to continue using this LiCoO ₂ as a positive electrode active material for a non-aqueous electrolyte secondary battery, the performance and performance of the non-aqueous electrolyte secondary battery are further improved. Life expectancy is desired.

In order to further improve the performance and life of a non-aqueous electrolyte secondary battery using such LiCoO ₂ as a positive electrode active material, it is essential to increase the capacity of the battery and improve the cycle life. By the way, in Patent Document 1 below, ₃ to 91.5 parts by mass of LiCoO ₂ as a positive electrode active material, 3 to 3 carbon black having a BET specific surface area of 100 to 400 m ² / g and a DBP oil absorption of 100 to 300 ml / 100 g are used. The nonaqueous electrolyte secondary battery including a positive electrode using a positive electrode mixture containing 4.5 parts by mass and 4 parts by mass of polyvinylidene fluoride (PVdF) as a binder has a capacity of 82 to 89% of the initial capacity after 500 cycles. It is shown that can be secured.

The non-aqueous electrolyte secondary battery disclosed in Patent Document 1 below has excellent cycle characteristics, but carbon black is 3.2 to 4.9 parts by mass of the positive electrode mixture, and PVdF is 4 parts by mass. A large amount is added, and the content ratio of LiCoO ₂ is reduced accordingly, so the battery capacity is reduced. In addition, the Patent Document 1, to increase the content of reducing the content of LiCoO ₂ of the carbon black, 93.5 parts by mass of LiCoO ₂ in the positive electrode mixture, the carbon black 2.5 It is also shown that when the mass part and PVdF are 4 parts by mass, the battery capacity after 500 cycles is reduced to 77% of the initial capacity.

On the other hand, LiCoO ₂ which is a positive electrode active material is exposed to a potential of 4 V or more on the basis of lithium at the time of charging. Therefore, when charging / discharging cycles are repeated, cobalt in LiCoO ₂ is eluted and deteriorates, and load performance is reduced. At the same time, the discharge capacity decreases. Therefore, during the synthesis of LiCoO ₂ that is the positive electrode active material, another transition element M is added and a different metal element added lithium cobalt oxide represented by the general formula LiCo _1-x M _x O ₂ is adopted. It is becoming. Since the elution of cobalt at the time of use of the dissimilar metal element-added lithium cobalt oxide represented by the general formula LiCo _1-x M _x O ₂ is suppressed, it is equal to or more than that when LiCoO ₂ is used alone. Various battery characteristics have been achieved.

For example, in Patent Document 2 below, a different metal element-added coprecipitated cobalt oxide obtained by coprecipitation of a lithium compound and an additive element M as a positive electrode active material (however, the additive element M includes Mg, Al, Cu, By using at least one selected from Zn), a non-aqueous electrolyte secondary battery having a high active material specific capacity, excellent charge / discharge cycle characteristics, and capable of suppressing an increase in battery thickness can be obtained. It is shown. Similarly, in Patent Document 3 below, as a positive electrode active material, a general formula Li _x Co _y M _z O ₂ (wherein M is at least one element selected from Mg, Al, Si, Ti, Zn, Zr and Sn). Is used, the phase transition is suppressed, the crystal structure is less disrupted, the thermal stability during charging is improved while maintaining high capacity, and good It has been shown that good charge / discharge characteristics can be realized.

  Further, in Patent Document 4 below, the positive electrode active material is composed of particles of a composite oxide containing lithium and cobalt, and the composite oxide includes an element M1 selected from the group consisting of Mg, Cu, and Zn, and Al. , Ca, Ba, Sr, Y and Zr, and an element M2 selected from the group consisting of Ca, Ba, Sr, Y and Zr. The element M1 is uniformly distributed in the particle, and the element M1 is more in the surface layer than in the particle. It has been shown that a non-aqueous electrolyte secondary battery that can achieve improved cycle characteristics and thermal stability without reducing the tap density of the positive electrode active material can be obtained by using a distributed material.

JP 2003-123764 A JP 2002-198051 A JP 2003-45426 A JP 2004 47437 A

As described above, the non-aqueous electrolyte secondary battery using the heterogeneous metal element-added lithium cobalt oxide in which different elements were homogeneously added by coprecipitation during the synthesis of LiCoO ₂ as the positive electrode active material used LiCoO ₂ alone. It is known that excellent cycle characteristics, thermal stability, load characteristics, and the like are exhibited. However, the battery capacity of the non-aqueous electrolyte secondary battery is reduced by an amount corresponding to an increase in the amount of the different element added to the lithium cobalt oxide containing the different metal element. On the contrary, if the content of LiCoO ₂ is increased by reducing the amount of different elements added in the lithium cobalt oxide added with different metal elements, the capacity of the nonaqueous electrolyte secondary battery can be increased. Characteristics, thermal stability, load characteristics, etc. are reduced. Therefore, in the conventional non-aqueous electrolyte secondary battery, when different elements are added to LiCoO ₂ that is the positive electrode active material, the improvement effect of cycle characteristics, thermal stability, load characteristics, etc. and the increase in battery capacity are compatible. It was difficult.

  The inventors have conducted various experiments in order to solve the problems of the prior art as described above, and as a result, used a lithium metal cobalt oxide having a different composition as a positive electrode active material and a positive electrode active material mixture. When carbon black having a predetermined physical property is used as a conductive agent, the battery capacity is reduced by reducing the amount of different metal elements added and the amount of carbon black added as a positive electrode conductive agent while maintaining cycle characteristics. As a result, the inventors have found that an increase in the number can be achieved, and have completed the present invention.

That is, the present invention uses LiCoO ₂ sintered so that different elements are uniformly dispersed as a positive electrode active material and carbon black having a specific composition as a conductive agent, and is particularly excellent in cycle characteristics and battery capacity. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a large current.

To achieve the above object, the non-aqueous electrolyte secondary battery of the present invention contains zirconium as a positive electrode active material, titanium, a sintered dissimilar metallic element-containing lithium-cobalt acid as aluminum and magnesium are homogeneously dispersed In a non-aqueous electrolyte secondary battery including a positive electrode having a positive electrode mixture, a negative electrode having a negative electrode mixture containing a negative electrode active material, and a non-aqueous electrolyte, the positive electrode mixture has a BET specific surface area of 60 to 100 m ² / g. And carbon black whose DBP oil absorption is 250-350 cm < ³ > / 100g is added , The addition amount of this carbon black is 1.0-2.0 mass% of positive mix, It is characterized by the above-mentioned.

That is, in the present invention, zirconium as different element, it is necessary to contain such homogeneously dispersed during titanium, cobalt compound is a synthetic raw material for the aluminum and magnesium lithium cobaltate prepared. In this case, zirconium as the different element, titanium, aluminum, magnesium free Chico these compounds, or when mixed firing LiCoO ₂ after, lithium compounds, cobalt raw material, zirconium raw material, titanium material, aluminum source and magnesium When raw materials are mixed and fired in a powdered state (dry mixed firing), a predetermined effect cannot be obtained because they are not homogeneously mixed, but different elements such as a coprecipitation method are simultaneously added to the cobalt compound at the same time. A predetermined effect can be obtained by using a method of synthesizing LiCoO ₂ after being contained.

Carbon black as a positive electrode conductive agent used in the present invention, it is necessary to BET specific surface area satisfies ^{60m 2} / ^g~100m 2 / g and DBP oil absorption 250cm ³ / 100g~350cm ³ / 100g conditions simultaneously . If the BET specific surface area of the carbon black is less than 60 m ² / g, the electrolyte solution has low liquid retention, so that a sufficient ion conduction path cannot be established and good cycle characteristics cannot be obtained. When the BET specific surface area of the carbon black exceeds 100 m ² / g, the conductive material in the slurry is poorly dispersed, and the state of the conductive material in the produced positive electrode plate can be biased. The reaction is likely to occur, and when charge / discharge cycles are repeated, the non-uniformity of the electrode reaction is promoted, and the cycle characteristics deteriorate.

Also, the BET specific surface area of carbon black as a positive electrode conductive agent is within the range of ^{60m 2 / g~100m 2 / g,} DBP oil absorption amount is structure development of the carbon black is less than 250 cm ^3/100 g can not be formed sufficiently conductive path due to insufficient, also, since the reaction DBP oil absorption is inhibited as the electrolytic solution at the time when the charge and discharge exceeds 350 cm ^3/100 g is uneven, either However, the cycle characteristics deteriorate.

  In the present invention, carbonates, lactones, ethers, esters and the like can be used as the nonaqueous solvent (organic solvent) constituting the nonaqueous electrolyte secondary battery. A mixture of the above can also be used. Among these, carbonates, lactones, ethers, ketones, esters and the like are preferable, and carbonates are more preferably used.

  Specific examples include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl. -1,3 oxazolidine-2-one, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, γ -Butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, 1,4-dio Xanthan can be mentioned.

In addition, as a solute of the nonaqueous electrolyte solution in the present invention, a lithium salt generally used as a solute in a nonaqueous electrolyte secondary battery can be used. Such lithium salts include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , and mixtures thereof Illustrated. Among these, LiPF ₆ (lithium hexafluorophosphate) is preferably used. When charged with a high charging voltage, becomes easily dissolved aluminum which is generally used as a current collector for the positive electrode, in the presence of LiPF _6, by the LiPF ₆ is decomposed, the aluminum surface coating formed Thus, dissolution of aluminum can be suppressed by this coating. Therefore, it is preferable to use LiPF ₆ as the lithium salt. The amount of solute dissolved in the non-aqueous solvent is preferably 0.5 to 2.0 mol / L. In addition, it is also possible to use a non-aqueous solvent and a solute that are made into a gel by containing them in an appropriate polymer.

  When the amount of carbon black added is less than 1.0% by mass of the positive electrode mixture, a sufficient electron conduction path cannot be formed in the positive electrode mixture even if different metal element-added lithium cobalt oxide is used. Cannot be obtained. If the amount of the conductive material exceeds 2.0%, the proportion of the conductive material in the positive electrode mixture is too large and a non-uniform battery reaction occurs.

  Moreover, in the nonaqueous electrolyte secondary battery of such an aspect, it is preferable that the addition amount of the different metal element-added lithium cobalt oxide is 95 to 98% by mass of the positive electrode mixture.

  When the addition amount of the lithium cobalt oxide added with the different metal element is less than 95% by mass of the positive electrode mixture, sufficient battery capacity cannot be secured, and the addition amount of the lithium cobalt oxide added with the different metal element is 98% by mass of the positive electrode mixture. If it exceeds 1, a sufficient amount of carbon black and binder as a conductive agent cannot be added, and battery characteristics deteriorate on the contrary.

  In the nonaqueous electrolyte secondary battery according to this aspect, the negative electrode active material is preferably made of a carbonaceous material.

  Since the battery voltage is indicated by the difference between the positive electrode potential and the negative electrode potential, the battery capacity can be increased by increasing the battery voltage. When 0.1V) is used, a non-aqueous electrolyte secondary battery having a high battery voltage and a high utilization rate of the positive electrode active material can be obtained. As the carbon material, natural graphite, artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or a mixture of one or more of these fired bodies can be used.

  According to the present invention, as will be described in detail below based on various examples and comparative examples, a nonaqueous electrolyte secondary battery having excellent active material filling properties and excellent storage stability can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using examples and comparative examples. However, the following examples illustrate one example of a nonaqueous electrolyte secondary battery for embodying the technical idea of the present invention, and are intended to specify the present invention in this example. Rather, the present invention can be equally applied to a variety of modifications without departing from the technical idea shown in the claims.

[ Reference Examples 1 to 4, Examples 1 to 7 ]
Initially, the specific manufacturing method of the nonaqueous electrolyte secondary battery of Reference Examples 1-4 and Examples 1-7 is demonstrated.

[Preparation of positive electrode active material]
A lithium metal cobalt oxide added with a different metal element as a positive electrode active material was prepared as follows. First, after adding one or more kinds of zirconium, titanium, aluminum, and magnesium dissolved in a predetermined amount of acid to the cobalt acid aqueous solution so as to have the compositions shown in Tables 1 to 3 below, Sodium hydrogen carbonate was added, and one or more of zirconium, titanium, aluminum, and magnesium were co-precipitated simultaneously with the precipitation of cobalt carbonate. Various ions are homogeneously mixed in the acid aqueous solution before the addition of sodium hydrogen carbonate, so that one or more of zirconium, titanium, aluminum and magnesium are homogeneous in the resulting cobalt carbonate precipitate. Is distributed. Thereafter, the cobalt carbonate co-precipitated with zirconium, titanium, aluminum, magnesium, etc. is subjected to a thermal decomposition reaction in the presence of oxygen, and zirconium, titanium, aluminum, magnesium, etc. as a starting material for the cobalt source are co-precipitated. Homogeneous tricobalt tetroxide was obtained.

  Next, lithium carbonate was used as a starting material for the lithium source, and lithium carbonate and zirconium, titanium, aluminum, magnesium, and the like were uniformly contained by coprecipitation so that the molar ratio of lithium to cobalt was 1: 1. Tricobalt oxide was weighed. Then, after mixing these compounds in a mortar, the obtained mixture was fired in air at 850 ° C. for 20 hours to synthesize a sintered body of a lithium metal cobalt oxide containing different metal elements containing zirconium, titanium, aluminum, magnesium and the like. did. Thereafter, the synthesized fired body was pulverized until the average particle size became 10 μm to obtain a positive electrode active material. The content of zirconium, titanium, aluminum, and magnesium in the obtained positive electrode active material was determined by analysis by ICP (Inductively Coupled Plasma) emission analysis.

[Production of positive electrode]
Weighed so that the dissimilar metal element-added lithium cobalt oxide powder was 97 parts by mass and the carbon black carbon powder as the positive electrode conductive material was 1 to 2 parts by mass so that the compositions shown in Tables 1 to 3 were obtained. Was mixed with polyvinylidene fluoride (PVdF) powder as a binder. Further, these mixtures were mixed with an N-methylpyrrolidone (NMP) solution to prepare a slurry. Next, this slurry was applied to both surfaces of an aluminum current collector with a thickness of 20 μm by a doctor blade method, and then dried and rolled to produce a positive electrode. Incidentally, carbon black as the positive electrode material, as shown in Table 1 to Table 3, BET specific surface area of 60~100m ² / g, and DBP oil absorption amount is 250~350cm ³ / 100g. The amount of binder used was (3% by mass−the amount of conductive material).

[Evaluation of physical properties of positive electrode conductive material]
The BET specific surface area of the carbon black used as the positive electrode conductive material was analyzed by the BET method, and the DBP oil absorption was measured by a method based on JISK-6221.

[Production of negative electrode]
A natural graphite powder was mixed at 95 parts by mass and a PVdF powder was mixed at 5 parts by mass, and this was mixed with an NMP solution to prepare a slurry. Next, this slurry was applied to both surfaces of a 18 μm thick copper current collector by a doctor blade method, and then dried and rolled to prepare a negative electrode. The potential of graphite is 0.1 V with respect to lithium. Moreover, the active material filling amount of the positive electrode and the negative electrode was adjusted so that the charge capacity ratio between the positive electrode and the negative electrode (negative electrode charge capacity / positive electrode charge capacity) was 1.1 at the potential of the positive electrode active material which is a design standard.

[Preparation of electrolyte]
LiPF ₆ was dissolved in an equal volume mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) so as to be 1 mol / L to obtain an electrolytic solution, which was used for battery production.

[Production of battery]
A cylindrical nonaqueous electrolyte secondary battery (height 65 mm, diameter 18 mm) having the configuration shown in FIG. 1 according to all of Reference Examples 1 to 4 and Examples 1 to 7 using the positive electrode, the negative electrode, and the electrolytic solution. ) Was produced. Note that a polypropylene microporous membrane was used for the separation overnight. The designed capacity of the manufactured non-aqueous electrolyte secondary batteries according to Reference Examples 1 to 4 and Examples 1 to 7 is 1500 mAh.

  Next, the specific manufacturing method of the nonaqueous electrolyte secondary battery of Comparative Examples 1-12 is demonstrated.

[Comparative Examples 1 and 2]
The non-aqueous electrolyte secondary battery of Comparative Example 1 is a reference example except that no different metal element is added to the lithium cobaltate used and the physical properties (BET specific surface area and DBP oil absorption) of the conductive agent to be added are different. 1 to 4 and in the same manner as in Example 1 . Moreover, the nonaqueous electrolyte secondary battery of Comparative Example 2 was produced in the same manner as in Reference Examples 1 to 4 and Example 1 except that no different metal element was added to the lithium cobalt oxide used.

[Comparative Examples 3 to 10]
The nonaqueous electrolyte secondary batteries of Comparative Examples 3 to 10 were prepared in the same manner as the nonaqueous electrolyte secondary batteries of Examples 2 to 5 except that the physical properties (BET specific surface area and DBP oil absorption amount) of the conductive agent to be added were different. did.

[Comparative Examples 11 and 12]
The nonaqueous electrolyte secondary batteries of Comparative Examples 11 and 12 were added with a conductive agent amount (carbon black amount).
These were produced in the same manner as in Examples 6 and 7 except that the difference was.

Next, a method for measuring the characteristics of the nonaqueous electrolyte secondary battery common to each reference example, example, and comparative example will be described.

The batteries of Reference Examples 1 to 4, Examples 1 to 7, and Comparative Examples 1 to 12 manufactured as described above were charged at a constant current of 1 It = 1500 mA at 25 ° C., and the battery voltage was 4.2 V. After that, the battery was initially charged at a constant voltage of 4.2 V until the charging current value reached 30 mA. The initially charged battery was discharged at a constant current of 1 It until the battery voltage reached 2.75 V, and the discharge capacity at this time was determined as the initial capacity.

[Cycle test]
About each battery of Reference Examples 1 to 4, Examples 1 to 7 and Comparative Examples 1 to 12 whose initial capacities were measured, the battery was charged at a constant current of 1 It at 25 ° C., and the battery voltage became 4.2 V Was charged at a constant voltage of 4.2 V until the charging current value reached 30 mA. Thereafter, the battery was discharged at a current value of 1 It until it reached 2.75 V, and the battery capacity in the discharge at this time was measured to obtain the reference capacity for the cycle test.

After that, again at 25 ° C., the battery is charged with a constant current of 1 It. After the battery voltage reaches 4.2 V, the battery is charged with a constant voltage of 4.2 V until the charging current value becomes 30 mA. Then, the discharge operation was repeated until 2.75V was reached, and the discharge capacity after 500 cycles was measured. And the cycle test result after 500 cycles was calculated | required by the following formulas using the reference | standard capacity | capacitance and the discharge capacity after 500 cycles.
Cycle test result (%)
= (Discharge capacity after 500 cycles / reference capacity) × 100

The measurement results of Reference Examples 1 to 4, Example 1 and Comparative Examples 1 and 2 are shown in Table 1, the measurement results of Examples 2 to 5 and Comparative Examples 3 to 10 are shown in Table 2 together with the measurement results of Example 1 , and The measurement results of Examples 6 and 7 and Comparative Examples 11 and 12 are shown in Table 3 together with the measurement results of Example 1 .

Table 1, different metal elements not added or added lithium cobalt oxide of 97 wt%, BET specific surface area of ^{80 m} 2 / g and DBP oil absorption of carbon black as a conductive agent 280 cm ^3/100 in those 1.5 wt% In addition, using a positive electrode active material mixture containing 1.5% by mass of a binder, no addition of zirconium, titanium, aluminum, or magnesium as a foreign metal element (Comparative Example 2), only 0.5% by mol of one type ( reference example) 1-4) The measurement result at the time of adding 0.5 mol% (Example 1 ) with four types is shown. Incidentally, other than the BET specific surface area of carbon black as a conductive agent is ^52m 2 / g and DBP oil absorption amount was used of 190 cm ^3/100 is simultaneously shows an example of adding the same manner as in Comparative Example 2 Comparative Example 1 is there.

  From the results shown in Table 1, the following can be understood. That is, in the batteries of Comparative Examples 1 and 2 in which the above different metal element is not added to lithium cobaltate, only a low result of 62 to 64% is obtained as a cycle test result. Further, from the results of Comparative Examples 1 and 2, it can be seen that the influence of the cycle test results is small even if the characteristics of carbon black as the conductive agent are changed unless a different metal is added to lithium cobalt oxide.

However, in the batteries of Reference Examples 1 to 4 and Example 1 in which the above different metal elements were added to lithium cobaltate, the results of the cycle test were significantly excellent as 80 to 84%. The reason why such a result was obtained is that the structure of lithium cobaltate is strengthened by adding a different metal element to lithium cobaltate, and the expansion / contraction is reduced even after repeated charge / discharge cycles. -It is presumed that the contact between the conductive materials does not deteriorate. The effect of adding a different metal element to this lithium cobaltate is good even when only one kind of zirconium, titanium, aluminum, or magnesium is added ( Reference Examples 1 to 4), but all four kinds are added. (Example 1 ) shows the best results.

  Therefore, to increase the active material addition ratio by reducing the amount of carbon black added as a conductive material, especially in order to increase the capacity, cobalt added with a dissimilar metal element with small expansion / contraction during charge / discharge The use of lithium acid is essential.

Table 2 shows a positive electrode active material mixture containing 97% by mass of a dissimilar metal element added or added lithium cobalt oxide, 1.5% by mass of carbon black as a conductive agent, and 1.5% by mass of a binder. Used, all added amounts of zirconium, titanium, aluminum, magnesium are 0
. 5 mol% constant, physical properties of carbon black as conductive agent (BET specific surface area and DB
The measurement results when the (P oil absorption amount) is changed are shown together with the measurement results of Example 1 . From the results in Table 2, it is possible to confirm the influence of the physical properties of carbon black as a conductive agent on the cycle test results.

That is, from the results shown in Table 2, the cycle test results is in the 83% or higher, BET specific surface area of ^{60m 2} / ^g~100m 2 / g and DBP oil absorption 250cm ³ / 100g~350cm ³ / It can be seen that the condition of 100 g is satisfied at the same time. This is because, when the positive electrode active material ratio is as high as 97% by mass, even when using a foreign metal element-added lithium cobaltate, the lithium cobaltate easily loses its conductivity due to the addition of the different metal element. It is shown that the improvement of the cycle characteristics cannot be achieved unless the state of the conductive material that surrounds is appropriate.

When the BET specific surface area of the carbon black as the conductive material is too low as less than 60 m ² / g under the compounding conditions of the different metal element-added lithium cobalt oxide, the conductive agent, and the binder as described above, the liquid retentivity of the electrolytic solution is low. Since it is low, a sufficient ion conduction path cannot be established, and satisfactory cycle characteristics cannot be obtained. Conversely, when the BET specific surface area of carbon black as a conductive material is too high, exceeding 100 m ² / g, the conductive material in the slurry is poorly dispersed, and the conductive material is present in the produced electrode plate. Due to the bias, non-uniform reactions are likely to occur. Therefore, when charge / discharge cycles are repeated, it is considered that the non-uniformity of the electrode reaction is promoted and the cycle characteristics are likely to deteriorate.

Also, the BET specific surface area of the conductive material have been defined to be a ^{60m 2 / g~100m 2 / g,} DBP oil absorption amount 250 cm ³ / If 100g and less than too small structure development is insufficient enough a conductive path can not be formed, because the DBP oil absorption is 350 cm ^3/100 g than the case too large the reaction is inhibited as a liquid at the time of charge and discharge become uneven, the both leads to a decrease in cycle characteristics Conceivable. Considering the conductivity of the lithium cobaltate active material with different metal element added, the liquid retention and dispersibility of the conductive material, carbon black as the conductive material used has a specific surface area of 60 to 100 m ² / g and a DBP oil absorption of 250. It needs to be -350cm < ³ > / 100g.

Table 3 shows that 97% by mass of the lithium cobaltate added with a different metal element is constant and the addition amount of carbon black as a conductive agent is changed from 0.5% by mass to 2.5% by mass. The measurement result when changing from 2.5% by mass to 0.5% by mass is shown together with the measurement result of Example 1 . Incidentally, carbon black as conductive agent, those all BET specific surface area of ^{80 m} 2 / g and DBP oil absorption amount of 280 cm ^3/100 g is used. In addition, the heterogeneous metal element-added lithium cobalt oxide is added in an amount of 0.5 mol% as a heterogeneous metal element for all of four kinds of zirconium, titanium, aluminum, and magnesium. From the results in Table 3, it is possible to confirm the influence of the amount of carbon black added as a conductive agent on the cycle test results.

  As is apparent from the results shown in Table 3, even when using a foreign metal element-added lithium cobalt oxide, if the amount of the conductive material to be added is too small, 0.5 mass% (Comparative Example 11), satisfactory cycle characteristics are obtained. Not obtained. This is presumably because the amount of the conductive agent was too small to form a sufficient electron conduction path in the positive electrode mixture, and a smooth charge / discharge reaction could not be performed. Conversely, when the amount of the conductive material is too large as 2.5% (Comparative Example 12), the cycle test result is lowered. This is presumably because the proportion of the conductive material in the positive electrode mixture is too large, causing a non-uniform battery reaction. Therefore, the optimum amount of carbon black added as the positive electrode conductive material in the present invention is 1.0 to 2.0% by mass of the positive electrode mixture.

  In each of the above examples, the example in which the content of the dissimilar metal element-added lithium cobalt oxide in the positive electrode mixture is 97% by mass is shown, but the present invention is not limited to this. The higher the content of the different metal element-added lithium cobalt oxide in the positive electrode mixture, the greater the capacity of the obtained nonaqueous electrolyte secondary battery, but the amount of carbon black added as the positive electrode conductive material is one of the positive electrode mixture. From the fact that 0.0 to 2.0% by mass is optimal and that the binder amount is required to be at least 1.0% by mass, the content of the dissimilar metal element-added lithium cobalt oxide in the positive electrode mixture is 98% by mass or less. Is the best. Moreover, since the capacity | capacitance of the nonaqueous electrolyte secondary battery obtained when the content of the different metal element addition lithium cobaltate in the positive electrode mixture decreases, at least 95% by mass or more is desirable.

It is a perspective view which cuts and shows the cylindrical nonaqueous electrolyte secondary battery to the vertical direction.

Explanation of symbols

10: nonaqueous electrolyte secondary battery, 11: positive electrode, 11a: current collecting tab, 12: negative electrode, 12a: current collecting tab, 13: separator, 14: spiral electrode body, 15, 16: insulating plate, 17: battery Exterior can, 18: Current blocking seal

Claims (3)

Having zirconium as the positive electrode active material, titanium, a positive electrode having a positive electrode mixture comprising a sintered dissimilar metallic element-containing lithium-cobalt acid as aluminum and magnesium are uniformly dispersed, the negative electrode mixture containing a negative electrode active material In a non-aqueous electrolyte secondary battery comprising a negative electrode and a non-aqueous electrolyte,
The BET specific surface area in the positive electrode mixture 60~100m ² / g and DBP oil absorption amount is added carbon black is 250~350cm ³ / 100g, the addition amount of the carbon black is 1.0 to the positive electrode mixture A non-aqueous electrolyte secondary battery characterized by being 2.0% by mass .   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the addition amount of the different metal element-added lithium cobalt oxide is 95 to 98 mass% of the positive electrode mixture. The negative active material non-aqueous electrolyte secondary battery according to any of claims 1 or 2, characterized in that it consists of carbonaceous material.

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