JPH03236173A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous electrolyte secondary battery with excellent characteristics by using a specific lithium containing vanadium oxide for the active material of a positive electrode, and adjusting the capacity ratio per unit area of a negative electrode against the positive electrode to 2.6-13. CONSTITUTION:In a lithium secondary battery using a lithium metal or a lithium alloy for a negative electrode active material, a lithium containing vanadium oxide expressed by the formula I or II is used for a positive electrode active material, and the thickness is adjusted so that the capacity ratio per unit area between a negative electrode 2 and a positive electrode 1 is preferably set to 3-7, where M indicates Na, K, Rb or Cs and 0<=x<=0.6, -0.5<=y<=0.3, 0<a<=0.5. A nonaqueous material such as LiPF6, LiAsF6, LiClO4 through which lithium ions can be electrochemically moved with the positive/negative electrode active materials is used for an electrolyte. The battery has a large capacity and a high potential and excellent cycle characteristics, and a stable charge/ discharge can be performed.

Description

[Detailed Description of the Invention] Emperor Retired Emperor Five Miles! The present invention relates to a nonaqueous electrolyte secondary battery using lithium or a lithium alloy as a negative electrode active material, and more specifically, to a nonaqueous electrolyte secondary battery that has a high potential, high energy density, and excellent cycle characteristics.

Many proposals have been made for high-energy density batteries that use lithium as the negative electrode active material, and lithium batteries that use fluorinated graphite or manganese dioxide as the positive electrode active material have already been developed. It is commercially available. However, these batteries are primary batteries and have the disadvantage of not being rechargeable.

For secondary batteries that use lithium as the negative electrode active material, titanium and molybdenum are used as the positive electrode active material.

Batteries using chalcogenides (sulfides, selenides, tellurides) of niobium, vanadium, and zirconium have been proposed, but few have been put into practical use because the battery characteristics and economic efficiency are not necessarily sufficient. recently,
Secondary batteries using molybdenum sulfide as the positive electrode active material have been put into practical use, but these also have drawbacks such as low discharge potential and vulnerability to overcharging. As a positive electrode active material with a high discharge potential, Li1. x V6O13 (X = 0.05 or x
= 0.2), and a secondary battery using this as a positive electrode has been proposed (J, Electrochem, Soc,
Vol, 133. Na 12゜P2454~24
58.1986). However, a secondary battery using such a positive electrode has a large capacity drop with charge/discharge cycles, and the capacity drops to nearly 50% after only about 20 cycles. For this reason, they have the disadvantage of having too short a lifespan to be used as a practical battery. For this reason, it is desired to develop a lithium secondary battery that has high energy density, particularly long charging/discharging life, stability, and reliability.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a nonaqueous electrolyte secondary battery that has a large capacity, a high potential, excellent cycle characteristics, and is capable of stable charging and discharging.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary comprising a positive electrode, a negative electrode made of lithium metal or an alloy containing lithium, and a non-aqueous electrolyte containing lithium ions. In the battery, as the active material of the positive electrode, the following formula +11 or (2) Lit, xV30a-v - (1) Lil
-g-aMaV30a+Y''<2) (wherein, M is Na, Rh, or Cs, and 0≦X≦0
．． 6. -0.5≦y≦0.3.0<a≦0.5)
A lithium-containing vanadium oxide represented by is used, and the capacity ratio per unit area of the negative electrode to the positive electrode is 2.6.
Provided is a nonaqueous electrolyte secondary battery characterized in that the electrolyte is adjusted to 13 to 13.

That is, as a result of examining the causes of deterioration in charge-discharge cycle performance of high-capacity, high-potential lithium secondary batteries, the present inventor found that the decrease in charge-discharge cycle life is due to deterioration of the positive electrode and the capacity ratio between the negative electrode and the positive electrode. was found to be an important factor. Therefore, in order to find a suitable positive electrode active material and a suitable capacity ratio between the negative electrode and the positive electrode for a lithium secondary battery that uses lithium metal or lithium alloy as the negative electrode active material, we have conducted further studies to find the following positive electrode active materials: Formula (1) or (
2) Lit-xVJs-v -(11Li t
Jx-aMaVJs,y-(2) (wherein M is Na, Rb or Cs, 0≦X≦0.6.-
0.5≦y≦0.3.0<a≦0.5) is used, and the capacity ratio of the negative electrode to the positive electrode is set to 2.4 to 13 per unit area (negative electrode/ By configuring a secondary battery with a negative electrode made of lithium metal or lithium alloy, and a nonaqueous electrolyte containing lithium, the battery has high capacity, high potential, and excellent cycle characteristics.
The present invention was completed based on the discovery that a non-aqueous electrolyte secondary battery that can be stably charged and discharged over a long period of time can be obtained.

The present invention will be explained in more detail below.

The positive electrode active material constituting the non-aqueous electrolyte secondary battery of the present invention has the following formula (11 or (2) Lit, xV+Os, v ++ (1) LI
++x−aMaV30s+y ++ (2)(
However, in the formula, M is Na, Rh, or Cs, and O≦X≦
0.6. -Q, 5≦y≦Q, 3. 0<a≦0.5).

Here, the lithium-containing vanadium oxide represented by the above (Formula 11) can be obtained by mixing vanadium pentoxide (V, 0.) and a lithium salt and firing the mixture, and in this case, the lithium salt is is LtzCOa +
LizO+ LINO:l + lithium oxalate,
Li salts of organic acids are used, especially LizCO3
is preferably used. Further, the mixing ratio of vanadium pentoxide and lithium salt is not particularly limited, but the V=Li ratio is 3:0.8 to 3:1.6, particularly 3:0.9 to 3:1.3.
It is preferable that Note that the firing temperature is not particularly limited, but is preferably 300 to 800°C.

Here, the value of X in L11+XVxO*-v is O~0.6
However, this value is the value at the time of synthesis or when charged to 3.5V or more, and the value of this X varies from 0 to 5 when charging and discharging.
It changes to a certain degree. Moreover, the value of y changes in the range of -0.5 to 0.3 depending on the oxidation state of vanadium (V). In addition, the more preferable range of x and y is that X is O to 0.3. y is −0,3 to 0.

Next, the lithium-containing vanadiram oxide represented by the above formula (2) can be obtained by replacing a part of the above lithium salt with Na and other alkali metal salts containing Rh or Cs. It can be obtained in the same way as in the case of equation 1). In this case, the anion species of the alkali metal salt to be substituted may be the same as or different from the anion species of the lithium salt, and specifically, CO:1z-I N03-I
CE-+ Br-, r-, 02-, OH-, 5CN-.

Examples include CH, COO-, and other organic acid anions. The amount of substitution of these alkali metal salts is represented by a in formula (2), and Q<a≦0.5, more preferably from 0.1 to 0.3. Note that the values of X and y in formula (2) are the same as in formula (11) above.

When creating a positive electrode using a lithium-containing vanadium oxide represented by the above formula (IJ or (2)) as an active material, the particle size of the positive electrode active material is not necessarily limited, but the average particle size is 3μ or less. A higher performance cathode can be made by using powders.In this case, conductive agents such as acetylene black and binders such as fluororesin powder are added and mixed with these powders, and the mixture is kneaded with an organic solvent. A positive electrode can be produced by a method such as rolling the material with a roll and drying it.

The amount of the conductive agent mixed is 3 parts by weight of the active material.
~25 parts by weight, especially 5 to 15 parts by weight,
In the present invention, since the active material has good conductivity, the amount of conductive agent used can be reduced. The amount of the binder added is 2 to 25 parts by weight per 100 parts by weight of the above positive electrode material.
Preferably, it is expressed in parts by weight.

As the negative electrode active material constituting the secondary battery of the present invention, lithium metal or a lithium alloy capable of intercalating and deintercalating lithium is used. In this case, the lithium alloy includes lithium-containing Ua, I[b.

Metals of the ma, IVa, and Va groups or alloys of two or more thereof can be used, but especially A II containing 80 mol% or more of lithium, In + Sn, Pb + at +
Cd + Zn or an alloy of two or more of these is preferred.

Furthermore, the electrolyte used in the secondary battery of the present invention is chemically stable with respect to the positive electrode active material and the negative electrode active material, and lithium L ions are mixed with the positive electrode active material acid or the negative electrode active material. Any non-aqueous substance that can move for electrochemical reaction can be used, specifically LiPFb + LiSbF6 + LiS
bF6, LiBF4. LiCj! 04+Lir
, LiBr, LiCj! , LiAlCl
, , LiHF2L1SCN, Li5ChCF3
etc. Among these, especially LiPFa +
LiAsF6. LiC1)4 is preferred.

Note that the electrolyte is usually used in a state dissolved in a solvent, and in this case, the solvent is not particularly limited, but a relatively highly polar solvent is preferably used. Specifically, cyclic carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate, acyclic carbonates I such as diethyl carbonate and dibutyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, and diethylene glycol dimethyl ether. ,
Lactones such as γ-butyrolactone, phosphoric acid esters such as triethyl phosphate, boric acid esters such as triethyl borate, sulfur compounds such as sulfolane and dimethyl sulfoxide, nitriles such as acetonitrile, dimethylformamide, dimethylacetamide, etc. Among these, cyclic carbonates such as ethylene carbonate and propylene carbonate are included!
, acyclic carbonates i such as diethyl carbonate, or a mixed solvent of two or more thereof is suitable.

Moreover, 3 to 10% by weight of aromatic hydrocarbons (benzene, toluene, etc.) can also be added to these solvents.

The non-aqueous electrolyte secondary battery of the present invention usually has the electrolyte interposed between the positive and negative electrodes, and if necessary, a nonwoven fabric or woven fabric made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene between the positive and negative electrodes. , a rope, etc. is used as a separator, and coin type, button type, and paper type are used.

Although it can be configured into batteries of various shapes such as cylindrical,
In this case, the secondary battery of the present invention has a capacity ratio of the negative electrode to the positive electrode of 2.6 to 13, preferably 3 to 7.
It has been adjusted to

Here, the method for adjusting the capacitance ratio per unit area of the negative electrode to the positive electrode (hereinafter referred to as C-/C+) to 2.6 to 13 is not particularly limited. Although a method of adjusting by increasing or decreasing the amount of active material or a method of adjusting by adjusting the thickness of the positive and negative electrodes can be adopted, a method of adjusting the thickness of the positive and negative electrodes is simple and preferred.

Although the non-aqueous electrolyte secondary battery of the present invention can have various forms as described above, it is particularly preferable to use a cylindrical secondary battery having a spiral structure electrode; in this case, the spiral structure electrode is Usually, a separator is arranged on both sides of a positive electrode sheet or a negative electrode sheet, in which active material sheets are laminated and integrated on both sides of a current collector sheet. Ru. In such a spiral structure electrode, both sides of the negative electrode face the positive electrode with a separator in between, so if we consider the positive electrode, separator, and negative electrode as one unit, half of the thickness of the negative electrode is opposite to the positive electrode. One side of each becomes a part involved in charging and discharging in the l unit. Therefore, in such a spiral structure battery, C-/C+ at half the thickness of the negative electrode and on one side of the positive electrode in one unit should be 2.4 to 1.
It is adjusted to 3. In addition, in other types of batteries, C-/C+ in similar units is 2.4 to 13.
It is important to adjust the

The nonaqueous electrolyte secondary battery of the present invention has a large capacity, a high potential, excellent cycle characteristics, and is capable of stable charging and discharging.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples below.

[Example 1] As positive electrode active materials, 1 mol of LizCOz and 3 mol of v
20. Li synthesized by firing at 750°C
Using VJs powder, 15 parts by weight of conductive carbon black as a conductive agent and 7.5 parts by weight of fluororesin powder as a binder were added to 100 parts by weight of the VJs powder, and after thorough mixing,
Kneaded with an organic solvent and rolled to approximately 300 μm with a roll,
It was vacuum dried at 150°C.

This was further rolled with a rolling roll to obtain a positive electrode sheet with a thickness of 102 μm. This was cut to a predetermined size and attached to both sides of stainless steel foil with a conductive adhesive containing carbon to form a positive electrode. In addition, as a negative electrode, a thickness of 15
A piece of 0 μm lithium foil cut into a predetermined size was used. C- between half of this negative electrode in the thickness direction and one side of the positive electrode
/C+ was 5.3.

Next, the integrated product in which a separator was inserted between the positive and negative electrodes was formed into a spiral shape around the core, and was housed in a cylindrical battery container. Then 1 mol/l LiPF
, into a non-aqueous electrolyte dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (1: 1), and the container was sealed to form a container with a height of 50.5 m and a diameter of 1 as shown in Figure 1.
I made 4.5 AA size batteries.

Here, in FIG. 1, l is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is a winding core, 5 is a battery container, 6 is a sealing gasket, and 7 is a partition.

[Example 2] A battery was produced in the same manner as in Example 1, except that a positive electrode with a 128 μm thick positive electrode sheet pasted only on one side of the current collector and a 108 μm thick negative electrode were used. C-/C+ is 3
．． It was 06.

[Example 3] A battery was produced in the same manner as in Example 1, except that a positive electrode with a 72 μm thick positive electrode sheet pasted only on one side of the current collector and a 204 μm negative electrode were used.

C-/C+ was 9.8.

[Comparative Example 1] A battery was produced in the same manner as in Example 1, except that a positive electrode with a 141 μm-thick positive electrode sheet pasted only on one side of the current collector and a negative electrode with a width of 85 μm were used.

C-/C+ was 2.05.

[Comparative Example 2] A battery was produced in the same manner as in Example 1, except that a positive electrode with a 50 μm thick positive electrode sheet pasted only on one side of the current collector and a 243 μm negative electrode were used.

C-/C+ was 16.9.

The batteries of Examples 1 to 3 and Comparative Example 1.2 were charged and discharged at a constant current of a discharge current of 15 (1+A) and a charging current of 75n+A with an end-of-discharge voltage of 2.OV and an end-of-charge voltage of 3.OV. Figure 2 shows the capacity at the third cycle and the number of cycles until the capacity reaches 65% of the capacity at the third cycle.

As is clear from the results shown in FIG. 2, the battery of the present invention has a high discharge capacity and good cycle characteristics, and is well-balanced as a secondary battery.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a cylindrical battery according to an example of the present invention, and FIG. 2 is a graph showing battery characteristics of batteries of the example and comparative example. ■...Positive electrode, 2...Negative electrode, 3...Separator,
4... Winding core, 5... Battery container, 6... Sealing gasket, 7... Partition wall.

Claims (1)

[Claims] 1. In a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode made of lithium metal or an alloy containing lithium, and a non-aqueous electrolyte containing lithium ions, the active material of the positive electrode is the following formula (1) or (2). )Li_1_+_xV_3O
_8_+_y...(1) Li_1_+_X_-_aM
aV_3O_8_+_Y...(2) (However, in the formula M
is Na, K, Rb or Cs, 0≦x≦0.6, -0.
5≦y≦0.3, 0<a≦0.5), and the capacity ratio per unit area of the negative electrode to the positive electrode was adjusted to 2.6 to 13. A non-aqueous electrolyte secondary battery characterized by: