JPH03289049A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolytic secondary battery having a large capacity and a high potential, excellent in low temperature characteristic, and allowing static charge and discharge by using a composite mainly containing a specific vanadium oxide as an active material for positive electrode. CONSTITUTION:A composite mainly containing a vanadium oxide represented by the formula 1 in which the value obtained by dividing the peak strength of 2theta=12.3 deg.+1 deg. in X-ray diffraction with CuK ray by the peak strength of 2theta=23.4 deg.+1 deg. is less than 0.5 is used as a positive electrode active material. This composite can be obtained by mixing vanadium pentoxide (V2O5) with a lithium salt and a sodium salt followed by baking. Hence, a nonaqueous electrolytic secondary battery having a large capacity and a high potential, excellent in low temperature characteristic and cycle characteristic, and allowing stable charge and discharge can be obtained.

Description

[Detailed Description of the Invention] The present invention relates to a nonaqueous electrolyte secondary battery using lithium metal or lithium alloy as a negative electrode active material, and more specifically, it has high potential, high energy density, and low temperature characteristics. This invention relates to a non-aqueous electrolyte secondary battery that has excellent properties.

Problems that conventional techniques attempt to solve
Many proposals have been made regarding high energy density batteries using lithium as a negative electrode active material, and lithium batteries using fluorinated graphite or manganese dioxide as a positive electrode active material are already on the market. However, these batteries are primary batteries and have the drawback of not being rechargeable.

For secondary batteries that use lithium as a negative electrode active material, titanium, molybdenum niobium, vanadium, and zirconium chalcogenides (fL compounds,
Batteries using selenides, tellurides) 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 a positive electrode active material have been put into practical use, but these also have drawbacks such as low discharge potential and vulnerability to overcharging. L1+* is a positive electrode active material with a high discharge potential.
*VJs (X = 0.05 or x = 0.2)
Examples include lithium-containing vanadium oxides shown in
A secondary battery using this as a positive electrode has been proposed (G,
Pistoia et al; J, Electro
chem, Soc, +νol.

133, floor 12. P2454-2458.1986
). However, a secondary battery using such a positive electrode has a relatively small initial capacity and a large capacity decrease with charge/discharge cycles. Therefore, the capacity increases by approximately 5 in just 20 cycles.
The battery life is too short to be used as a practical battery. Another problem is that the discharge capacity is significantly reduced at low temperatures of −5° C. or lower. Therefore, it is desired to develop a lithium secondary battery that has high energy density, particularly long charge/discharge life, and has excellent low-temperature characteristics, 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 non-aqueous electrolyte secondary battery that has a large capacity, a high potential, excellent low-temperature characteristics and cycle characteristics, and is capable of stable charging and discharging. shall be.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte comprising a positive electrode, a negative electrode whose active material is lithium metal or an alloy containing lithium, and a non-aqueous electrolyte containing alkali metal ions. In a water electrolyte secondary battery, Li + - is used as the active material of the positive electrode.
x-yNayV30a-z (0,1≦x≦0.4.0
．． 1≦y<0.7. -0.5≦z≦0.3) A composition mainly composed of vanadium oxide shown in C
It is characterized in that the value obtained by dividing the peak intensity at 20 = 12.3° ± 1° by the peak intensity at 2θ = 23.4° ± 16 in X-ray diffraction using uKg rays is 0.5 or less. To provide a non-aqueous electrolyte secondary battery.

That is, the inventor first determined that Li + +xV:+Os+y
By replacing part of the lithium (0≦x≦0.6.-0.5≦y≦0.3) with other alkali metals such as Na and K, the interplanar spacing of the crystal is partially expanded. They discovered that lithium ions can be easily inserted into the cathode material and that it can be a high-performance cathode material with good stability, and proposed a battery using such a cathode material (Japanese Patent Application No. 2-211).
No. 41), we measured the low-temperature properties (ratio of capacity at low temperature to capacity at room temperature: low-temperature capacity retention rate) of this positive electrode material, and found that the low-temperature capacity retention rate was also improved, especially for Na substitution. This was newly discovered. However, this Na substituent is similar to the above L! 1+xVJ1
- When X of y is smaller than 0.1, that is, the sum of Li salt and Na salt is for 3 vanadium (V) atoms of V2O5,
It has been found that when the ratio is 1.1 atoms or less, β-Na and V2O3 mixed as by-products during synthesis reduce the capacity per unit weight. Therefore, this Na substitution product, namely L1+-xNayVioe-jO, l≦x≦0
．． 4, 0.1≦y〈0.7. -0.5≦z≦0.3) As a result of further study on the vanadium oxide expressed by
a, xV20. , by adjusting the value obtained by dividing the peak intensity of 2θ = 12.3° ± 1°, which indicates the amount, by the peak intensity of 2θ = 23,4' ± 16, to be 0.5 or less,
A positive electrode material with improved low-temperature capacity retention without reducing capacity per unit weight can be obtained, and this can be used to produce a battery positive electrode, which is then combined with a negative electrode containing lithium metal or lithium alloy as an active material and lithium ions. discovered that a non-aqueous electrolyte secondary battery with high potential, high energy density, and excellent low-temperature characteristics could be obtained by combining a non-aqueous electrolyte containing This is what I did.

The present invention will be explained in more detail below.

As mentioned above, the non-aqueous electrolyte secondary battery of the present invention has L
l + +X-1'Nal' 30B-(0,1≦x≦
0.4.0.1≦y<0.7. -0.5≦z≦0.3)
The main component is vanadium oxide represented by CuK e
The value obtained by dividing the peak intensity at 2θ = 12.3° ± 16 by the peak intensity at 2θ = 23.4° ± 1° in X-ray diffraction using t-rays (hereinafter 1, □, 3/T Z: 1.4) ) is 0
．． 5 or less is used as a positive electrode active material.

Here, the above composition includes vanadium pentoxide (VzOs)
It can be obtained by a method such as mixing a lithium salt and a sodium salt and firing the mixture. In this case, the lithium salts include lithium carbonate (LizCO:+), lithium oxide (LizO), lithium nitrate (LiNO:+),
Lithium oxalate (Li ZC204), lithium iodide (Lil), lithium bromide (LiBr), organic acid L
i salts and their hydrated salts are used, but especially Li
2CO3 is preferably used. Further, as the sodium salt, the above-mentioned lithium salt in which Li is replaced with Na can be used, and Na and C03 are particularly preferably used.

The non-aqueous electrolyte secondary battery of the present invention uses vanadium oxides containing alkali metals (Li+Na) obtained in this way that have a 11□, 3/I 23.4 of 0.5 or less. There is, but ■1□, 3/I214 is 0.
5 or less, in the above production method, vanadium pentoxide (V2O5) and alkali metal salt (L
This can be carried out by appropriately selecting the mixing ratio of the lithium salt and the sodium salt (i salt + Na salt), the mixing ratio of the lithium salt and the sodium salt, the synthesis (calcination) temperature, the synthesis (calcination) time, the material of the firing container, etc. Specifically, vanadium pentoxide (VzO
The mixing ratio of s) and alkali metal is vandium (■):
The alkali metal (Li+Na) ratio is 3:1.1 to 3:1.
5 (molar ratio), particularly preferably from 3:1.15 to 3:1.25, and the mixing ratio of lithium salt and sodium salt is 1.1:0.1 to 0.5 (Li:Na). 5:
The ratio is preferably 0.7, particularly 1.1:0.1 to 0.8:0.04. The firing temperature is 350 to 800
°C, especially when using alkali metal carbonates, 650 °C
~750°C, baking time can be 4 to 8 hours,
A quartz or platinum container is preferably used as the firing container. By appropriately selecting these conditions depending on the type of lithium salt and sodium salt used, etc., II2. :
The value of 1/I23.4 can be controlled. Note that the atmosphere during firing can be air or oxygen atmosphere.

The positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention has a value of 11□, :l/I 23.4 of 0 by the above method or the like.
．． The vanadium oxide containing the alkali metal controlled to have an alkali metal concentration of 5 or less is more preferable, and it is more preferable to use one that does not exhibit a peak peak at 2θ=12.3°±1° in X-ray diffraction using CuKa rays. Also, LI I+x−yNayVsca+
The X and y values of z are 0.1≦x≦0.4.0, respectively.
．． Although 1≦y<0.7, these values are values at the time of synthesis, and the value of X changes by up to about 5 due to charging and discharging, and the value of y may also change slightly. Moreover, the value of 2 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 this Xy is 0.15 to 0.25. y is 0.1 to 0.4
It is.

When creating a positive electrode using vanadium oxide containing the above-mentioned alkali metal as an active material, the particle size of the oxide is not necessarily limited, but if one with an average particle size of 3μ or less is used, higher performance can be achieved. A positive electrode can be made. In this case, the positive electrode is prepared by adding and mixing a conductive agent such as acetylene black or a binder such as fluororesin powder to these powders, kneading with an organic solvent, rolling with a roll, and drying. can be created. The amount of the conductive agent mixed is 3 to 25 parts by weight, especially 5 parts by weight, per 100 parts by weight of the active material.
-15 parts by weight, and in the present invention, since the active material has good conductivity, the amount of conductive agent used can be reduced.

Further, the amount of the binder to be blended is preferably 2 to 25 parts by weight per 100 parts by weight of the positive electrode material.

As the negative electrode active material constituting the secondary battery of the present invention, lithium or a lithium alloy capable of intercalating and deintercalating lithium is used. In this case, the lithium alloys include II a + II b and III a + I containing lithium.
Va, Va group metals or alloys of two or more thereof can be used, especially /ll+In+Sn containing lithium,
Pb, Bi, Ca, Zn, or an alloy of two or more of these are preferred. In particular, when forming a cylindrical battery, it is preferable that the molar fraction of lithium in the alloy be 80% or more.

Further, 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 ions are electrically connected to the positive electrode active material acid or the negative electrode active material. Any non-aqueous substance that can move for chemical reaction can be used, specifically LiPF6. LiAsFi,, LiS
bF6. LiBFa, LiCAO, LilLiBr
, LiC1! , LiA I C124, Li
HF2+ Li5CN.

Examples include Li5O and CF2. Among these, especially LIPF br LIASF&1 LiCIt Oa
is suitable.

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, butylene carbonate, acyclic carbonates such as diethyl carbonate, dibutyl carbonate, and grime such as tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, and diethylene gelcol dimethyl ether. kind,
Lactones such as T-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. Examples include one or a mixture of two or more of amides, dimethyl sulfate, nitromethane, nitrobenzene, dichloroethane, and the like. Among these, particularly preferred are one or more mixed solvents selected from cyclic carbonates such as ethylene carbonate and propylene carbonate, and acyclic carbonates such as diethyl carbonate.

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 is usually constructed by interposing an electrolyte between the positive and negative electrodes, but in this case, a separator is interposed between the positive and negative electrodes to prevent current short-circuiting due to contact between the two electrodes. can do. As the separator, it is possible to use porous materials that allow the electrolyte to pass therethrough, such as nonwoven fabrics, woven fabrics, and nets made of synthetic resins such as polytetrafluoroethylene, polypropylene, and polyethylene. Furthermore, a solid electrolyte that serves both as an electrolyte and a separator can also be used.

Note that the form of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and may be in various forms such as a spiral-structured cylindrical battery, a coin type, a button type, a paper type, etc.

The non-aqueous electrolyte secondary battery of the present invention has a large capacity, a high potential, excellent low-temperature 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] 3 mo/L/(7) vzos and 0.92 mole LizC
After thoroughly mixing O:+ and 0.31 mol of Na2CO=, the mixture was placed in a quartz crucible and reacted by heating at 630°C in the air for 6 hours, then the melt was poured into a copper block and cooled.
An oxide composition containing Li and Na was obtained.

This composition was pulverized into a powder, and X-ray diffraction (CuKα
), no peak appeared at 2θ=12.3′±1° (see Figure 2). In addition, the results of elemental analysis of this composition show that the ratio of Li atoms to 3 atoms is 0.9.
0. The Na atom was 0.31.

Therefore, this composition has Li0. , Nao, 31Vl
It is indicated by o8.

Acetylene brane as a conductive agent was added to 100 parts by weight of this powder.
Add 15 parts by weight of fluororesin powder and 15 parts by weight of fluororesin powder as a binding side, mix thoroughly, knead with an organic solvent, roll to about 100 μm with a roll, vacuum dry at 150 ° C,
A battery positive electrode was created by punching out the material to a predetermined diameter.

Using the above battery positive electrode, a lithium foil punched to a predetermined size was used as the negative electrode, and 1.5 liters of lithium/phosphorus hexafluoride (LtPF) was added to a mixed solvent of propylene carbonate and ethylene carbonate (volume ratio 7:3). The battery shown in FIG. 1 was assembled using the solution dissolved in mol/l as an electrolyte.

Here, in FIG. 1, 1 is a positive electrode, 2 is a positive electrode current collector made of stainless steel, the positive electrode 1 and the current collector 2 are integrated, and the current collector 2 has a spacer 3 made of a metal plate. spot welded.

Further, this spacer 3 is spot welded to the inner surface of the positive electrode can 4. 5 is a negative electrode, 6 is a negative electrode current collector, and the negative electrode 5 is spot-welded to the negative electrode current collector 6 fixed to the inner bottom surface of the negative electrode can 7. Furthermore, 8 is a separator made of staghorn propylene, which is impregnated with the electrolytic solution.

Note that 9 is an insulating backing. Also 1. The battery dimensions are 20mm in diameter. On, the thickness is 1.6 mm.

This battery was charged and discharged at room temperature with a charge/discharge current of 1 mA and a discharge end voltage of 2. Charging and discharging were repeated at OV and a charge end voltage of 3.5V. Table 1 shows the capacity per active material in the third cycle.

Next, after charging this battery to 3.5V at room temperature, -1
Place the battery in a low temperature chamber at 0°C, discharge after the temperature of the battery has fallen to the set temperature, measure the discharge capacity up to 2 OV, and calculate the ratio of the discharge capacity to the capacity at the third cycle at the above room temperature. It was calculated as a capacity retention rate. The results are shown in Table 1.

[Example 2] 3-11-Luno V2O5 and 1 mo/L/(7) Liz
A V oxide composition containing Li and Na was obtained by mixing C (h) and 0.2-E/L/NazCO, and using this mixture as a raw material in the same manner as in Example 1. When the X-ray diffraction of the object was measured in the same manner as in Example 1, 2θ=
No peak appeared at 12.3°±1° (see Figure 3).

In addition, as a result of elemental analysis of this composition, Lio, qNa
o, zv303.

A battery similar to that in Example 1 was assembled using this composition.

Regarding this battery, as in Example 1, the discharge capacity per active material (room temperature) at the third cycle and the discharge capacity (at room temperature) at the fourth cycle (
-10°C) to determine the low-temperature capacity retention rate. The results are shown in Table 1.

[Example 3] 3 mol (D VzOs and 0.7-El Li2CO
3 and 0.5 mol of Na2CO1, and using this mixture as a raw material, Li and Na were prepared in the same manner as in Example 1.
A V oxide composition containing the following was obtained. When X-ray diffraction of this composition was measured in the same manner as in Example 1, no peak appeared at 2θ=12.3°±1°. In addition, as a result of elemental analysis of this composition, Lio, ) Nao, 411V30
? , 95.

A battery similar to that in Example 1 was assembled using this composition.

Regarding this battery, the discharge capacity at the third cycle (room temperature) and the discharge capacity at the fourth cycle (-10°C) were measured in the same manner as in Example 1, and the low-temperature capacity retention rate was determined. The results are shown in Table 1.

[Example 4] 3-T-L (7) V2O3 and 1.1 mol 0:) L
Mix izC03 with 0.1 mol of Na2CO1,
Using this mixture as a raw material, L was prepared in the same manner as in Example 1.
A V oxide composition containing i and Na was obtained. When xvA diffraction of this composition was measured in the same manner as in Example 1, 2θ=
No peak appeared at 12,3'±1°. Moreover, as a result of elemental analysis of this composition, Li 1. as)Jao
, l IV307.92.

A battery similar to that in Example 1 was assembled using this composition.

Regarding this battery, the discharge capacity at the third cycle (room temperature) and the discharge capacity at the fourth cycle (-1σ°C) were measured in the same manner as in Example 1, and the low-temperature capacity retention rate was determined. The results are shown in Table 1.

[Comparative Example 1] 3) IiO) vzos and 0.7 mol of Li2CO
3 and 0.3 mol of NazCO3, and using this mixture as a raw material, Li, l!
: An oxide composition containing Na was obtained. X of this composition
When line diffraction was measured in the same manner as in Example 1, 2θ = 1
It has a peak at 2.3°±1°, and I I 2. *
/I 23.4 was 26 (see Figure 4). In addition, as a result of elemental analysis of this composition, Lio, Jao,
It was confirmed that it was shown by ff2v3oI IIs.

A battery similar to that in Example 1 was assembled using this composition.

Regarding this battery, the discharge capacity at the third cycle (room temperature) and the discharge capacity at the fourth cycle (-10°C) were measured in the same manner as in Example 1, and the low-temperature capacity retention rate was determined. The results are shown in Table 1.

[Comparative Example 2] 3 moles (7) of VzOs and 1 mole of Li2C0 were mixed, and a V oxide composition containing Li and Na was obtained in the same manner as in Example 1 using this mixture as a raw material. When the XwA diffraction of this composition was measured in the same manner as in Example 1, no peak appeared at 2θ = 12.3° ± 1''. Also, as a result of elemental analysis of this composition, L,...96
V30? , 'I was confirmed.

A battery similar to that in Example 1 was assembled using this composition.

Regarding this battery, the discharge capacity at the third cycle (room temperature) and the discharge capacity at the fourth cycle (-10°C) were measured in the same manner as in Example 1, and the low-temperature capacity retention rate was determined. The results are shown in Table 1.

No. table

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the present invention, and FIGS. 2 to 4 are graphs showing X-ray diffraction patterns of batteries of Examples 1 and 2 and Comparative Example 1, respectively. ■... Positive electrode, 2... Positive electrode current collector, 3... Positive electrode can,
4... Negative electrode, 5... Negative electrode current collector, 6... Negative electrode can,
7... Separator 8... Insulating backing.

Claims (1)

[Scope of Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode using lithium metal or an alloy containing lithium as an active material, and a non-aqueous electrolyte containing alkali metal ions, wherein the active material of the positive electrode is As a substance, Li_1_+_x_-_yNa_yV_3O_8_+_
z (However, 0.1≦x≦0.4, 0.1≦y<0.7,
-0.5≦z≦0.3), which has a composition mainly composed of vanadium oxide, which shows 2θ=12.3°± by X-ray diffraction using CuKα rays.
A nonaqueous electrolyte secondary battery characterized in that the value obtained by dividing the peak intensity at 1° by the peak intensity at 2θ=23.4°±1° is 0.5 or less.