JP2000195513A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that satisfies practical performance over a wide temperature range and contains a lithium- manganese composite oxide as the main active material for the positive electrode. SOLUTION: In relation to a nonaqueous electrolyte secondary battery provided with a negative electrode active material capable of storing and releasing lithium, and a mixed positive electrode active material comprising a lithium ion conductive nonaqueous electrolyte and a lithium containing metal composite oxide capable of storing and releasing lithium, the mixed positive electrode active material of this nonaqueous electrolyte secondary battery is a mixture of a lithium-manganese-based composite oxide having a spinel structure expressed by a general formula Li[LiαM βMn2-α-β]O4-γAγ with a lithium-nickel- based composite oxide having a layer structure expressed by a general formula Li[LixNi1-x-y-zCoyTz]O2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to improve the practical performance of a non-aqueous electrolyte secondary battery, including its storage characteristics and cycle characteristics.

[0002]

2. Description of the Related Art With the recent development of electronic technology, devices have been reduced in size and weight at a surprising speed. For this reason, mobile devices such as mobile communication devices and portable computers have begun to spread widely, and secondary batteries having a high energy density have been demanded as power sources for these mobile devices. Above all, non-aqueous electrolyte secondary batteries can be expected to have a higher voltage than conventional nickel-cadmium batteries or nickel-metal hydride batteries, and are therefore in great demand as power sources that can be expected to further reduce the size and weight of equipment. However, in a nonaqueous electrolyte secondary battery using lithium metal and lithium alloy as a negative electrode material, when charge and discharge are repeated, dendritic projections of lithium are formed on the negative electrode, and cycle performance is reduced,
It has not been put to practical use because of problems such as reliability at high temperatures.

As means for solving these problems, a non-aqueous electrolyte using a carbon material capable of inserting and extracting lithium as a negative electrode active material and a composite oxide of lithium and a transition metal having a layered structure as a positive electrode active material. Secondary battery (patent 19
No. 89293), which has a voltage of 4 V or more in a charged state, and is widely used as a power source for mobile devices. However, current non-aqueous electrolyte secondary batteries are expensive because they use LiCoO2 containing a large amount of cobalt as a positive electrode material, and there is a limit in reducing the price as a power source. For this reason, attempts to replace cobalt oxide with nickel oxide or manganese oxide are active. LiNiO2 is inexpensive compared to LiCoO2 and can improve the energy density of the battery, but it has a problem in ensuring the safety of the battery, especially at an abnormally high temperature of about 150 ° C. On the other hand, LiMn2O4 is LiNiO
Compared to 2, the price is lower, and it is possible to construct a battery with excellent safety at the time of overcharge or abnormally high temperature. Therefore, it is most expected that LiCoO2 can be replaced.

[0004]

However, lithium manganese oxide having a stoichiometric composition has poor cycle performance, and in order to improve this, manganese is replaced with another transition metal such as cobalt (for example, see Patent No. 2,058,834), as described in JP-A-5-205744, substituting a part of manganese with lithium.
As disclosed in Japanese Patent No. 54403, it has been proposed to partially replace oxygen with F. However, when charge and discharge are repeated at high temperatures, manganese is eluted, and there is a problem that satisfactory cycleability cannot be obtained.

[0005] In addition, LiCoO2 or LiNiO2 is mixed with LiMn2O4 for the purpose of imparting ionic conductivity to the active material, and the amount of combination with carbon as the negative electrode active material is specified to thereby improve the cycle characteristics at 40 ° C. An invention that attempts to achieve safety during charging is disclosed in Japanese Patent Application Laid-Open No. Hei 7-235291, but has problems in high-temperature storage characteristics of about 85 ° C. and safety reliability after overdischarge.

Also, LiMn2O4 causes volume contraction when Li ions escape, while Li (NixCo1-x) O2 causes volume expansion when Li ions escape. Japanese Patent Application Laid-Open No. 8-45498 discloses an invention that achieves a high battery capacity by suppressing the volume change, improving the cycle characteristics, and compensating for the low capacity of LiMn2O4. It was found that there were problems with the cycle characteristics, storage characteristics under high temperature, and safety reliability.

Therefore, in a nonaqueous electrolyte secondary battery using a lithium manganese composite oxide as a main active material of a positive electrode, cycle characteristics in a wide range from room temperature to about 60 ° C.
Satisfies practical performance as a non-aqueous electrolyte secondary battery, such as storage stability in a charged state and a discharged state at about 0 to 85 ° C., and safety reliability during overcharge and safety reliability after overdischarge. The technology has not been established yet. In recent years, the increase in the clock frequency of the CPU in recent computers has caused
The heat generated inside the main unit is large, and the temperature inside the main unit rises to 40 ° C or more even during normal use. The battery used as a power source has cycle characteristics at high temperatures, stable storage characteristics, Safety after discharge is required more than ever, and it is urgent to solve the problem.

The present invention provides a non-aqueous electrolyte secondary battery that uses lithium manganese composite oxide as a main active material of a positive electrode and satisfies practical performance in a wide temperature range.

[0009]

In view of such circumstances, the present inventors have made intensive studies on the improvement of practical performance including storage characteristics and cycle characteristics of a non-aqueous electrolyte secondary battery using a lithium manganese composite oxide as a main active material. As a result, the present invention has been achieved. That is, the present invention provides a mixed positive electrode active material comprising a negative electrode active material capable of inserting and extracting lithium, a lithium ion conductive nonaqueous electrolyte, and a lithium-containing metal composite oxide capable of inserting and extracting lithium. In the non-aqueous electrolyte secondary battery provided with the substance, the mixed positive electrode active material has a general formula Li
[LiαMβMn2-α-β] O4-γAγ (where 0 ≦
α ≦ 0.12, 0 <β ≦ 0.20, 0 ≦ γ ≦ 0.05, M is at least one selected from Al, Cr, Ni, and A is selected from F, Cl A lithium manganese-based composite oxide having a spinel structure represented by at least one of the following general formulas: Li [LixNi1-xy-zCo
yTz] O2 (where 0 ≦ x ≦ 0.03, 0 ≦ y ≦ 0.
3, 0 ≦ z ≦ 0.05, and T is Al, Mg, B, S
a non-aqueous electrolyte secondary battery which is a mixture of a lithium-nickel-based composite oxide having a layered structure represented by the following formula: The ratio of the initial lithium storage capacity (Q) P / Q of the positive electrode using the positive electrode active material is 1.0 or more and 1.25 or less, and the initial current efficiency of the positive electrode is smaller than the initial current efficiency of the negative electrode. It is an electrolyte secondary battery.

Hereinafter, the present invention relates to a lithium manganese composite oxide, a lithium nickel composite oxide, a negative electrode active material,
Specific description will be made in the order of these combinations. The manganese raw material of the lithium manganese composite oxide used in the present invention is not particularly limited.
electrical Mangane Dioxide), CMD (Chemical Man
gane Dioxide), γ-MnOOH, and MnCO3, but EMD is preferably used because the specific surface area of the obtained lithium manganese oxide can be reduced. Also,
Lithium raw materials include Li2CO3, LiOH, LiNO3, Li2S
O4 and CH3COOLi can be mentioned, and Li2CO3 and LiOH are preferable. Along with these manganese raw materials and lithium raw materials, as replacement metal materials, oxides such as Cr2O3, NiO, hydroxides such as Al (OH) 3, Al2 (SO4) 3, Cr (NO3) 3, Cr2 (SO4) 3, NiSO
4. It is possible to add a chloride such as Ni (NO3) 2, but an oxide or hydroxide that does not involve generation of NOx or SOx is preferable. In addition, LiCl, LiF,
Can be mixed with the raw material.

The method for producing the lithium manganese composite oxide is not limited. For example, when M is aluminum and A is fluorine, it can be produced as follows. A mixture of EMD, Li2CO3, Al (OH) 3, and LiF pulverized so that the average particle size becomes 5 to 25 μm is Li / (Mn + A
l) = 0.50, and after mixing so that the F amount becomes a desired amount, heat treatment is performed at 750 to 950 ° C. in the atmosphere. Here, the replacement amount of manganese sites by Al is preferably 0.2 or less. 0.
If it exceeds 2, the capacity becomes small and is not practical. The heat treatment temperature is preferably as high as possible because the specific surface area can be reduced. However, at 950 ° C. or higher, a phase other than spinel which is not lost even in the next second heat treatment is generated. After heat-treating these mixtures, they are cooled to around room temperature and Li2CO3
Was added to a desired Li / (Mn + Al) ratio, and mixed.
By performing heat treatment at 0 to 700 ° C, more preferably 500 to 650 ° C, a lithium manganese composite oxide having a desired composition can be obtained. Further, the atomic ratio of Li / (Mn + Al) at the 16d site, which is the final manganese site, that is, the amount of replacement with lithium is 0.064 or less.
If it exceeds 0.064, the capacity is significantly reduced, and it is difficult to obtain a single spinel layer.

In another example, pulverized EMD and Li2C
The mixture of O3, Al (OH) 3 and LiF
It is also possible to carry out heat treatment by mixing so as to obtain the (Mn + Al) ratio, the Al / Mn ratio, and the F amount. Heat treatment is 60
The reaction is carried out at 0 to 850 ° C, more preferably at 650 to 800 ° C. Heat treatment at a temperature lower than 600 ° C. increases the specific surface area and the contact area with the electrolytic solution.
The elution of n increases and the cycle characteristics and storage characteristics deteriorate. Further, in a heat treatment higher than 850 ° C., a phase other than spinel is generated, so that the capacity is reduced and the cycle characteristics are deteriorated.

The specific surface area of the obtained lithium manganese composite oxide is 1.5 m2 / g or less, preferably 1 m2 / g or less, more preferably 0.5 m2 / g or less. If it is larger than 1.5 m2 / g, the cycle characteristics at high temperatures and the high-temperature storage characteristics will deteriorate. Also, for the purpose of removing Li2SO4 derived from raw materials,
It is also possible to wash the obtained heat-treated product. Although the specific surface area may be increased by washing, the specific surface area after washing may be within the above range.

The element that replaces the manganese site and the amount thereof can be appropriately selected within a certain range according to the purpose in order to affect the final performance of the battery. According to the study of the present inventors, when lithium is replaced by lithium alone, although the capacity decreases in accordance with the replacement amount, the cycle characteristics at high temperatures are dramatically improved. On the other hand, Al and Cr,
When substituted with Ni, the high-temperature storage characteristics are dramatically improved. Therefore, it is possible to improve the energy density, high-temperature cycle characteristics, and high-temperature storage characteristics of the battery in a well-balanced manner, and to dramatically improve the high-temperature cycle characteristics or the high-temperature storage characteristics. That is, it may be appropriately selected according to the request of the device using the battery. Among these, a case where a mixture of a lithium nickel composite oxide and a lithium manganese composite oxide substituted with Al, Cr, and Ni is used is preferable, and the energy density, high temperature cycle characteristics, and high temperature storage characteristics are balanced. It is possible to improve well. This is because the addition of lithium-nickel composite oxide allows the negative electrode to absorb lithium ions that are not used in normal discharge, and makes it possible to supplement the deactivation of lithium ions at the negative electrode, resulting in good high-temperature cycle characteristics. In addition to the high-temperature storage characteristics,
The lithium manganese composite oxide itself is further improved because it is dramatically improved.

Next, the lithium nickel composite oxide used in the present invention will be described. Although the nickel raw material is not particularly limited, for example, NiO, Ni (OH) 2, Ni (NO
3) 2, NiCO3. Lithium raw materials, for example, Li
2CO3, LiOH, LiNO3, Li2SO4, CH3COOLi can be mentioned. Above all, when Ni (NO3) 2 is used, Ni (OH) 2 and L
A combination of iOH or a combination of NiCO3 and LiNO3 is preferable because a single layered compound is easily obtained.
Further, a combination of Ni (OH) 2 and LiOH that does not generate NOx or SOx is preferable. However, when a so-called coprecipitation method is used for the purpose of uniformly mixing Co and Ni, it is preferable to use a sulfate or a nitrate. Along with these nickel raw materials and lithium raw materials, cobalt raw materials (Co3O4, CoO, Co (OH) 2, CoSO
4, Co (NO3) 2) plus B2O3, Mg (OH) 2, Sr (OH) 2, Mg
(NO3) 2, Sr (NO3) 2, and the like can be appropriately added.

The method for producing the lithium-nickel composite oxide is not limited. For example, when a part of nickel is replaced with cobalt and T is magnesium, it can be produced as follows. Ni (OH) 2, LiOH and Co
(OH) 2, Mg (OH) 2 is uniformly mixed with a mixer such as a ball mill so that Li / (Ni + Co + Mg) = 1.02, and then mixed in air or in a mixed atmosphere of oxygen and air at 600 to Heat treatment is performed at 750 ° C. Here, the atomic ratio of cobalt to nickel is 0.1.
484 or less is preferable. If it exceeds 0.484, the capacity is reduced, and the initial charging efficiency of the mixed positive electrode is too high.
When the heat treatment temperature is outside this range, the capacity decreases.

[0017] As another production method, a coprecipitation method can be mentioned. Ni (NO3) 2, Co2 (NO3) 2, and Mg (NO3) 2 are dissolved and mixed in purified water at a desired ratio, and a NaOH aqueous solution is slowly added dropwise to obtain a precipitate. This is washed with water, mixed with Li2CO3 as a raw material so that Li / (Ni + Co + Mg) = 1.02, and heat-treated. The heat treatment conditions are the same as above. In addition, it is preferable that each heat-treated product is washed with purified water after the heat treatment in order to remove a hydroxide that did not contribute to the reaction.

The synthesized lithium manganese composite oxide and lithium nickel composite oxide are mixed with 50:50 to 90:
The mixture was mixed at a weight ratio of 10 to obtain a positive electrode active material. The mixing range is appropriately selected depending on the capacity of each active material and the combination amount with the negative electrode active material. However, when the content of the lithium manganese composite oxide becomes 50% by weight or less,
It becomes difficult to suppress abnormal heat generation during overcharge. Further, the content of the lithium nickel composite oxide is 10% by weight.
In the following, it is difficult to maintain the battery performance even after overdischarge, and the high-temperature cycle characteristics are liable to deteriorate.

The negative electrode material used in the present invention is not particularly limited as long as it can occlude and release lithium in an ion state. Examples thereof include carbon such as coke, natural graphite, artificial graphite and non-graphitizable carbon, and metal oxides such as SiSnO. , B
Although a carbon composite material such as CN and SiC can be used, it is preferable to use carbon having high initial current efficiency because the energy density of the battery can be increased.

In the present invention, when the active material is formed into an electrode, a conductive agent can be added as required, and the active material can be fixed to the current collector with a binder. Examples of the conductive agent include natural graphite, artificial graphite, carbon black, Ketjen black, and acetylene black, and graphite or a combination of graphite and acetylene black is preferred. Although the addition amount is not particularly limited, it is preferably 1 to 20% by weight, more preferably 3 to 10% by weight. 1% by weight
If it is less than the above, the conductivity will not be uniform, and if it exceeds 20% by weight, the capacity per unit volume will decrease. Further, the binder is usually polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, carboxymethylcellulose, styrene butadiene rubber,
Fluororubber or the like is used alone or as a mixture,
There is no particular limitation. The amount of these additives is preferably 1 to 20% by weight, more preferably 1 to 10% by weight. If it is 1% by weight or less, the binding force is weak, and if it is 20% by weight or more, the movement of Li ions is inhibited, and the performance as a battery is reduced.

As the electrolytic solution, a mixture in which a lithium salt is used as an electrolyte and dissolved in various organic solvents is used. The electrolyte is not particularly limited.
O4, LiBF4, LiPF6, LiAsF6, LiC
A single or a mixture such as F3SO3 can be used. The organic solvent is not particularly limited. Examples thereof include propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate,
-A single solvent such as dimethoxyethane and tetrahydrofuran or a mixture of two or more solvents can be used.

The method of measuring the initial lithium release and occluding capacity of the positive electrode and the negative electrode and the initial current efficiency of both electrodes in the present invention will be described. A three-electrode cell is prepared using the obtained positive or negative electrode as a working electrode and metallic lithium as a counter electrode and a working electrode. At this time, it is necessary to minimize the distance between the working electrode and the counter electrode as much as possible in order to eliminate the influence of the liquid resistance of the electrolytic solution.
It is preferable to sandwich a glass filter having a thickness of about 5 mm and press both poles from outside. The reference electrode also needs to be placed near the working electrode. An electrolytic solution is injected into the obtained cell, and after allowing it to stand overnight, charging and discharging are performed under the following conditions. As the electrolytic solution, it is preferable to use the same electrolytic solution as when the obtained positive electrode and negative electrode are actually used in combination. In addition, it is desirable to leave the apparatus overnight to wait for the electrolyte to permeate the electrode.

The charging and discharging conditions are as follows. In the case of the positive electrode, the maximum current value is set to 3 mA / cm2, and the potential of the working electrode is 4.
The battery is charged at a constant current and a constant voltage for 5 hours so that the voltage becomes 25 V, and then a 30-minute rest period is provided after the charging, followed by discharging. For discharging, set the current value to 3 mA / cm2, and the potential of the working electrode
Perform until 3.5V is reached. The initial lithium dischargeable capacity of the positive electrode can be obtained by dividing the integrated current amount flowing during charging by the area of the working electrode. Further, the initial lithium storage capacity (Q) of the positive electrode is calculated by dividing the integrated current amount flowing during discharge by the area of the working electrode. Therefore, the unit of Q is usually
mAh / cm2. The quotient obtained by dividing the integrated current amount flowing during discharging by the integrated current amount flowing during charging is defined as the initial current efficiency, and is usually expressed in%.

On the other hand, in the case of the negative electrode, the maximum current value is 3 mA / cm 2
, And constant-current constant-voltage discharge (lithium insertion) is performed for 5 hours so that the potential of the working electrode becomes 0.01 V. Then 30
After a pause of 1 minute, the battery is charged. Charging (release of lithium) is performed until the electric potential of the working electrode reaches 1.0 V with the current value set to 3 mA / cm2. The initial lithium storage capacity of the negative electrode can be obtained by dividing the integrated current flowing during discharge by the area of the working electrode. In addition, the initial lithium releaseable capacity (P) of the negative electrode is calculated by dividing the integrated current flowing during charging by the area of the working electrode. Therefore, the unit of P is usually mAh / cm2. The quotient obtained by dividing the integrated current flowing during discharging by the current flowing during integrated charging is defined as the initial current efficiency, and is usually expressed in%.

In the present invention, the combination amount of the positive electrode and the negative electrode is important. This combination amount is defined by the above P and Q. That is, it is important that P / Q is 1.0 or more and 1.25 or less. When the value is less than 1.0, that is, when the lithium releaseable capacity of the negative electrode is smaller than the lithium storage capacity of the positive electrode, the potential of the negative electrode increases at the end of discharge, and the battery voltage decreases. Also 1.
Above 25, the energy density of the battery decreases because the amount of lithium ions stored in the negative electrode that cannot be released at a normal battery voltage (for example, 3.0 V) increases.

The optimum value of this combination is determined by the mixing ratio of the lithium manganese composite oxide and the lithium nickel composite oxide in the active material used for the positive electrode, the initial current efficiency of the mixed active material, and the initial current efficiency of the negative electrode. It is possible to Normally, the non-aqueous electrolyte secondary battery uses the above P / Q
Is about 0.8 to less than 1.0. This is because the initial current efficiency of the positive electrode using LiCoO2 is usually about 97%, while the initial charging efficiency of the negative electrode using carbon is 90% even when graphite, which is said to be high, is used. This is because when discharging the battery, lithium ions cannot be released from the negative electrode, and the potential of the negative electrode increases to reach the discharge end voltage of the battery. By the way, although the initial current efficiency of the positive electrode using LiMn2O4 is 95% or more even when the manganese site is replaced, when a mixture of the lithium manganese composite oxide and the lithium nickel composite oxide of the present invention is used as an active material, The initial current efficiency can be changed depending on the amount of the lithium-nickel composite oxide and the substitution element and the amount of the nickel site. The initial current efficiency of the mixed positive electrode is preferably less than the initial current efficiency of the negative electrode to 80% or more. If it is less than 80%, the energy density of the battery decreases. Further, when the current efficiency is equal to or higher than the initial current efficiency of the negative electrode, not only safety after overdischarge is reduced, but also high-temperature cycle characteristics are reduced. This is understood as follows.

At the time of overdischarge, as described above, since there is no releasable lithium ion in the negative electrode, the potential of the negative electrode continues to rise to the potential of the positive electrode. As a result, the potential becomes higher than the oxidation-reduction potential of copper used for the negative electrode current collector, and elutes as copper ions into the electrolytic solution. At the time of charging after the overdischarge, the copper ions precipitate in the form of a negative electrode, which causes an internal short circuit and abnormal heat generation. On the other hand, when the combination as in the present invention is used, the potential of the positive electrode decreases during overdischarge, and abnormal heat generation does not occur during recharge. Furthermore, in a battery using LiMn2O4, manganese elutes from the positive electrode during high-temperature cycling and precipitates on the negative electrode, and the capacity of the battery decreases due to charge exchange with lithium ions. Because of the presence of lithium ions, it is possible to prevent a decrease in capacity during a high-temperature cycle.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to these examples.

[0029]

Example 1 EMD pulverized to an average particle size of 20 μm was used as a starting material. This and Li2SO4, Al (OH) 3, LiF
/ (Mn + Al) / F = 1 / (1.9 + 0.1) /0.01 (atomic ratio), mixed in a ball mill for 3 hours, heat-treated in air at 850 ° C for 20 hours, and then around 10 hours near room temperature Cooled down.
Next, the lithium manganese composite oxide and Li2CO3 were
/(Mn+Al)=0.53 (atomic ratio), and the mixture was again heat-treated in air at 650 ° C. for 20 hours to obtain a lithium-manganese composite oxide. As a result of analysis by atomic absorption and back titration, α = 0.04, β = 0.1, γ = 0.0
Was one.

The lithium nickel composite oxide was synthesized by a precipitation method. Ni (NO3) 2 and Co (NO3) 2, Mg (NO3) 2 7.9
The mixture was mixed at 7: 2: 0.03, dissolved in purified water, and an aqueous NaOH solution was added dropwise with stirring. The precipitate was filtered and washed to obtain a nickel cobalt magnesium composite hydroxide. Next, LiOH and the composite hydroxide are mixed so that Li / (Ni + Co + Mg) = 1.02, and heat-treated at 550 ° C. for 20 hours and then at 700 ° C. for 3 hours. A nickel composite oxide was obtained. As a result of analysis by atomic absorption and back titration,
x = 0.01, y = 0.2, z = 0.03.

Next, a specific example of battery production will be described.
The lithium manganese composite oxide and the lithium nickel composite oxide were mixed at a ratio of 8: 2, and 3 parts by weight of acetylene black and 3 parts by weight of scale-like natural graphite were mixed as a conductive agent with this mixture 100, and then the total weight was mixed. Was mixed with PVdF at a ratio of 3 parts by weight, and NMP which was a solvent for PVdF was added to perform wet mixing to obtain a paste. Next, this paste was uniformly applied to both sides of a 20-μm-thick aluminum foil serving as a positive electrode current collector, dried, and then pressure-formed by a roller press to form a belt-shaped positive electrode. Next, 1 part by weight of carboxymethyl cellulose and styrene-butadiene rubber 2 were added to a mixture of mesocarbon fiber 95 graphitized at 3000 ° C. and scale-like natural graphite 5.
By weight, purified water was added as a solvent and wet-mixed to obtain a paste. Next, this paste was uniformly applied to both sides of a copper foil having a thickness of 12 μm as a negative electrode current collector, dried, and then pressed and formed by a roller press to form a strip-shaped negative electrode. Furthermore, a 25 μm-thick polyethylene microporous membrane was interposed between the positive electrode and the negative electrode as a separator, wound up in a roll around an elliptical core, and after the core was removed, pressing was performed to obtain an elliptical wound body. And

Next, the wound body was inserted into a rectangular outer can made of aluminum. The negative electrode tab taken out from the wound body was welded to a negative electrode pin provided at the center of the closing lid provided with the electrode pressing plate, and the positive electrode tab was welded to the closing lid. The closure lid was placed on an outer can, and the joint between the can and the closure lid was welded by laser. Furthermore, a diameter of 0.5 m provided on the closing lid body
An electrolyte obtained by dissolving LiPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / liter is injected from a hole of m into an aluminum thin plate, and a thin aluminum plate is placed on the hole, and the periphery of the thin plate is laser-welded. 6mm thick
A square nonaqueous electrolyte secondary battery having a width of 30 mm and a length of 48 mm was prepared.

Thereafter, the coating amounts of the positive electrode and the negative electrode were adjusted so that the initial lithium release capacity of the positive electrode and the initial lithium storage capacity of the negative electrode became equal. As a result, the ratio of the initial lithium release capacity (P) of the negative electrode and the initial lithium storage capacity (Q) of the positive electrode used in this battery was P / Q = 1.0.
It was 6. The initial current efficiency of the positive electrode was 85%, and the initial current efficiency of the negative electrode was 90%.

Next, the test method will be described. (High temperature storage test) After a 24-hour aging period has elapsed for the purpose of stabilizing the inside of the battery, the charging voltage is set to 4.2 V.
And charging was performed in 5 hours. Then 550mA
The battery was discharged at a constant current of 3.0 V to 3.0 V, and the capacity of each battery was measured. Next, the battery was charged in 3 hours with the charging voltage set to 4.2 V, then placed in a thermostat adjusted to 85 ° C., and taken out after 120 hours. After the battery was naturally cooled to around room temperature, the battery was discharged to 3.0 V at a constant current of 550 mA, charged at a charging voltage of 4.2 V for 3 hours, and discharged at a constant current of 550 mA. The retention rate was calculated from the discharge capacity after storage and the discharge capacity before storage, and the recovery rate was calculated from the discharge capacity when recharged after storage and the discharge capacity before storage. (High-temperature cycle test) The initial charge of the battery requires a charge voltage of 4.2.
V was set at 5 hours. Then, the battery was discharged at a constant current of 550 mA to 3.0 V, and the capacity of each battery was measured.

Next, the battery is placed in a thermostat at 60 ° C.
A charge / discharge cycle test was performed in which the battery was charged at a charging voltage of 4.2 V for 3 hours and discharged at a constant current of 550 mA to 3.0 V, and the maintenance rate of the discharge amount with respect to the first cycle of the 100th cycle was defined as the cycle maintenance rate. (Overcharge test) After about 10 cycles of discharging and charging after initial charging, a 10 V 1.5 A DC power supply was connected to the discharged battery. At this time, battery leakage, gas ejection,
The presence or absence of ignition was observed. (Overdischarge test) After about 10 cycles of discharging and charging after the initial charge, the discharge voltage was set to 0 V from the fully charged state, and the battery was forcibly discharged for 48 hours. The maximum current value at this time is 5
It was 50 mA. After forced discharge, the charging voltage is 4.2V
, And charged so that the battery was fully charged in 3 hours.
At that time, the presence or absence of battery leakage, gas ejection, and ignition was observed.

The results of these evaluations are shown in Table 1.

[0037]

Examples 2 to 4 The mixing weight ratio of the lithium manganese composite oxide and the lithium nickel composite oxide was 90% each.
Example 1 except that / 10, 60/40 and 50/50 were used.
In the same manner as in the above, a square nonaqueous electrolyte secondary battery was prepared. Table 1 shows the initial discharge capacity, P / Q, and various test results of the battery at this time.
It was shown to.

[0038]

Comparative Examples 1 and 2 The mixing weight ratio of the lithium manganese composite oxide and the lithium nickel composite oxide was 10% each.
A rectangular nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 0/0 and 40/60 were set. Table 1 shows the initial discharge capacity, P / Q, and various test results of the obtained battery.

[0039]

Examples 5 to 7 EMD pulverized to an average particle size of 15 μm as a starting material and Li2SO4, Cr2O3 and LiCl were converted to Li / (Mn + Cr) / Cl
= 1 / (1.85 + 0.15) /0.005 (atomic ratio), except that the mixture and heat treatment were performed in the same manner as in Example 1 except that α = 0.04,
A lithium manganese composite oxide having β = 0.15 and γ = 0.005 was obtained.

Ni (NO 3) 2, Co (NO 3) 2 and Sr (NO 3) 2 as starting material compositions of the lithium nickel composite oxide were 6.98: 3:
X = 0.01 in the same manner as in Example 1 except that it was set to 0.02,
A lithium nickel composite oxide having y = 0.3 and z = 0.02 was obtained. These are respectively 90/10, 80/20, 50/50
A rectangular non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that a mixed positive electrode active material was obtained by mixing at a weight ratio of Table 2 shows the initial discharge capacity, P / Q, and various evaluation results of these batteries.

[0041]

Comparative Examples 3 and 4 A prismatic nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 5, except that the mixing ratios of the mixed positive electrodes were 100/0 and 40/60. Table 2 shows the initial discharge capacity, P / Q, and various evaluation results of these batteries.

[0042]

Examples 8 to 11 As starting materials for a lithium manganese composite oxide, EMD and Li ground to an average particle size of 15 μm were used.
Lithium having a different Mn: Al ratio was obtained by mixing and heat treating in the same manner as in Example 1 except that the mixing amount of 2SO4 and Al (OH) 3 was adjusted so that the Al content had a composition ratio as shown in Table 3. A manganese composite oxide was obtained.

As the starting material composition of the lithium-nickel composite oxide, the mixing amount of Ni (NO3) 2, Co (NO3) 2, and Mg (NO3) 2 is fixed at an amount of Mg of 0.03. The mixture was mixed so as to have a value as shown in FIG. 3, and a lithium nickel composite oxide was obtained in the same manner as in Example 1. The obtained positive electrode active materials were mixed at a weight ratio of 70/30 to obtain a mixed positive electrode active material. Subsequently, a prismatic nonaqueous electrolyte secondary battery was prepared in the same procedure as in Example 1. Table 3 shows the initial discharge capacity, P / Q, and various evaluation results of the obtained batteries.

[0044]

Comparative Examples 5 and 6 In the same manner as in Examples 8 and 9, a lithium-manganese composite oxide having an Al content shown in Table 3 and a lithium-nickel composite oxide having a Co content shown in Table 3 in the same manner Were mixed at the mixing ratios shown in Table 3 to obtain a mixed positive electrode active material, and a rectangular nonaqueous electrolyte secondary battery was prepared in the same procedure as in Example 1. Table 3 shows the initial discharge capacity, P / Q, and various evaluation results of the obtained batteries.

[0045]

Examples 12 to 14 The starting material had an average particle size of 10 μm.
m was used. This and Li2SO4 are Li / Mn = 1
The mixture was mixed in a ball mill at a composition ratio of 1/2 (atomic ratio) for 3 hours, heat-treated in air at 900 ° C. for 10 hours, and then cooled to around room temperature over 10 hours. Then, the lithium manganese oxide and Li2CO3 are mixed so that Li / Mn = 1.1 / 1.9 (atomic ratio), and heat-treated again at 650 ° C. for 20 hours in air to obtain α = 0.1, β = 0, A lithium manganese composite oxide with γ = 0 was obtained.

The lithium nickel composite oxide was prepared by mixing Ni (NO 3) 2 and Co (NO 3) 2 as starting materials in a ratio of 8: 2, dissolving in purified water, and dropping an aqueous NaOH solution with stirring. The precipitate was filtered and washed to obtain a nickel-cobalt composite hydroxide. Next, LiOH and a composite hydroxide, B / (Co + Ni) = 0.01 / 0.9
B2O3 in an amount of 9 was mixed with Li / (Ni + Co + B) = 1.03, and the mixture was heated at 550 ° C. for 20 hours and then at 700 ° C.
Heat treatment for 3 hours, cooling and washing with water, x = 0.0
2. A lithium nickel composite oxide having y = 0.2 and z = 0.01 was obtained.

Both are 90/10, 80/20, 60/4
A prismatic nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the components were mixed at a weight ratio of 0. Table 4 shows the initial discharge capacity, P / Q, and various evaluation results of the obtained batteries.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

[0051]

[Table 4]

[0052]

As described above, the present invention is based on the combination of a specific ratio of the mixed positive electrode and the negative electrode of the lithium manganese composite oxide and the lithium nickel composite oxide.
Good cycle characteristics over a wide temperature range, good storage characteristics at high temperatures, and high energy density that prevents abnormal heat generation during overcharge and abnormal heat after overdischarge, that is, practical performance Can be obtained. Furthermore, it is inexpensive because expensive cobalt is not used. As a result, it is possible to provide a non-aqueous electrolyte secondary battery that is comparable to a case where expensive lithium cobalt oxide is used, using a low-cost material lithium manganese composite oxide as a main active material. A high-performance non-aqueous electrolyte secondary battery can be supplied at low cost, and its industrial value is great.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA01 BB05 BC01 BC05 BC06 BD00 BD03 5H014 AA01 CC01 EE10 HH01 HH04 5H029 AJ02 AK03 AL01 AL02 AL06 AL07 AL08 AM03 AM04 AM05 AM07 DJ16 DJ17 HJ01 HJ02 HJ16 HJ19

Claims (3)

[Claims] 1. A mixed positive electrode active material comprising a negative electrode active material capable of inserting and extracting lithium, a lithium ion conductive non-aqueous electrolyte, and a lithium-containing metal composite oxide capable of inserting and extracting lithium. In a non-aqueous electrolyte secondary battery provided with a substance, the mixed positive electrode active material is represented by the general formula Li [LiαMβMn2-α-β] O4-γAγ (where 0 ≦ α ≦ 0.12, 0 <β ≦ 0.20 , 0 ≦
γ ≦ 0.05, M is at least one selected from Al, Cr, and Ni, and A is at least one selected from F and Cl.) A composite oxide and a general formula Li [LixNi1-xy-zCoyTz] O2 (where 0 ≦ x ≦ 0.03, 0 ≦ y ≦ 0.3, 0 ≦ z ≦
0.05, and T is at least one selected from the group consisting of Al, Mg, B, and Sr.) A non-aqueous electrolyte secondary battery that is a mixture of lithium nickel-based composite oxides having a layered structure represented by the following formula: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium nickel-based composite oxide having the layered structure contained in the mixed positive electrode active material is 50% by weight or more and 10% by weight or less. 3. The capacity of the negative electrode to release lithium for the first time (P)
And the ratio P / Q of the initial lithium storage capacity (Q) of the positive electrode using the mixed positive electrode active material is 1.0 or more and 1.25 or less, and the initial current efficiency of the positive electrode is greater than the initial current efficiency of the negative electrode. The non-aqueous electrolyte secondary battery according to claim 1, wherein the secondary battery is also small.