JPH1173965A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery with high capacity and superior cycle characteristic by suppressing the deposition of lithium to a negative electrode in the charge of a nonaqueous electrolyte lithium secondary battery, having a positive electrode containing a positive active material capable of releasing/absorbing lithium ions in charge/discharge and a negative electrode containing carbon capable of absorbing/releasing lithium ions in charging/discharging. SOLUTION: Carbon fluoride is added to the negative electrode of a battery. Thereby, lithium ions equivalent to the irreversible capacity of a positive electrode in a first cycle charge react with the additive having large reaction amount per volume with the ions and are fixed to the negative electrode. As a result, the increase in volume of the negative electrode is suppressed, and in addition, the conductivity of the negative electrode is increased by carbon produced in the reaction. A battery design capable of ensuring sufficient filling amount of an active material and suppressing the deposition of lithium to the negative electrode in charge is made possible, and the battery with high capacity and superior cycle characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention provides a non-aqueous electrolyte lithium secondary battery, particularly a battery having excellent charge / discharge cycle characteristics and high capacity.

[0002]

2. Description of the Related Art In recent years, portable electronic devices have become more portable.
Cordless use is rapidly progressing. Conventionally, nickel-cadmium batteries, nickel-metal hydride batteries or sealed small lead-acid batteries have played a role as a power supply for driving these electronic devices, but as these devices have become smaller, lighter and more multifunctional, Demands for higher energy density, smaller size and lighter weight of a secondary battery serving as a driving power source are increasing. Under such circumstances, various positive electrode active materials have been proposed. Among them, a lithium composite transition metal oxide exhibiting a high charge / discharge voltage, for example, LiCoO 2
₂ (for example, JP-B-63-59507), and LiNiO ₂ (for example, U.S. Pat.
02518), a composite oxide of a plurality of metal elements and lithium, for example, Li _y Ni _x Co _1-x O ₂ (JP-A-63-299).
056 _{JP), Li x M y N 2} O (M: Fe, Co, N
at least one selected from i, N: Ti, V, C
at least one selected from r and Mn)
-267053). Various nonaqueous electrolyte secondary batteries using these as a positive electrode active material and using a carbon material capable of inserting and extracting lithium ions for a negative electrode have been proposed. LiCoO ₂ has already been used for a positive electrode, and a carbon material has been used for a negative electrode. Batteries using Pt have been put to practical use. Among these positive electrode active materials, LiNiO ₂ is being actively researched and developed as a promising active material because LiNiO ₂ has a particularly stable supply of Ni as a raw material and is expected to be inexpensive and have a high capacity. .

[0003]

However, the positive electrode active materials reported so far, in particular, LiNi _x M _{1 -x} O ₂ (M is at least one of Co, Mn, Cr, Fe, V, and Al) , X: 1 ≧ x ≧ 0.5), the first cycle charge (lithium release reaction) and discharge (lithium release reaction) in the potential region (4.3 V to 2 V with respect to Li) which is usually used as a battery. It is known that there is a large difference in charge / discharge capacity during the lithium storage reaction (for example, A. Rougerie).
t al. Solid State Ionics 9
0,83 (1996). Lithium ions (Li ⁺ ) corresponding to this charge / discharge capacity difference (positive electrode irreversible capacity) are irreversible, and are ions that are released from the positive electrode during charging but cannot be absorbed by discharging. Usually, the percentage of the amount of Li ⁺ occluded by the discharge with respect to the amount of Li ⁺ released by the charge in the first cycle is called the charge / discharge efficiency of the positive electrode active material. In particular, the above-mentioned LiNi _x M _1-x O ₂ , The charging and discharging efficiency is low.

In the case of a negative electrode material, Li ⁺ due to discharge with respect to the amount of Li ⁺ absorbed due to the charge in the first cycle.
Is referred to as charge / discharge efficiency. As a negative electrode material of such a non-aqueous electrolyte secondary battery, about 90%
A carbon material such as graphite exhibiting the above high charge / discharge efficiency is used.

As shown in FIG. 1, when a secondary battery using a positive electrode having lower charge / discharge efficiency than a negative electrode is constructed, Li ⁺ released from the positive electrode by the first cycle charging is occluded by the negative electrode, and Li ⁺ corresponding to the reversible capacity of the positive electrode is released from the negative electrode, but the amount of Li ⁺ corresponding to the irreversible capacity of the positive electrode remains on the negative electrode even after the end of discharge. Li ⁺ remaining on the negative electrode has a reversible capacity of the positive electrode smaller than that of the negative electrode despite the fact that it can be discharged. (Capacity indicated by A in FIG. 1), and a capacity corresponding to a capacity (negative electrode irreversible capacity) that cannot be essentially discharged by the discharge reaction while being fixed to the negative electrode.

The reversible Li of the carbon material of the negative electrode is⁺
Storage capacity, that is, the reversible charging capacity is limited.
For example, if graphite is used for the negative electrode, C₆37 equivalent to Li
2 mAh / g is the limit, amorphous carbon material other than graphite
In some cases, a larger limit is shown. I
However, if you try to charge beyond this limit, Li ⁺
Is reduced to deposit metallic lithium on the surface of the negative electrode.
The released metallic lithium easily reacts chemically with the electrolyte.
Moles are electrochemically inert and desorb from the negative electrode body
This reduces the charge / discharge efficiency and reduces battery cycle characteristics.
Properties will be significantly reduced.

That is, in the state where Li ⁺ corresponding to the remaining reversible capacity which cannot participate in charge / discharge shown in FIG. 1A is held in the negative electrode carbon, the reversible electric capacity of the negative electrode which can be charged in the second cycle and thereafter. Becomes smaller. For this reason, there is a problem that the chargeable / dischargeable electric capacity of the battery is reduced, and that the amount of electricity exceeding the limit of the reversible electric capacity is easily supplied during charging, so that metallic lithium is easily deposited on the negative electrode surface.

As a measure for solving the above problems,
Even in a state in which all the Li ⁺ released by the positive electrode in the first cycle of charging is occluded in the negative electrode, a method of increasing the amount of carbon used for the negative electrode is considered in order to leave sufficient reserve capacity for the occlusion capacity of the negative electrode. As a result, the deposition of metallic lithium due to charging is suppressed, but the space occupied by the increased amount of carbon is large, and it is necessary to correspondingly reduce the amount of the active material to be charged, and as a result, the battery capacity is reduced. Will be.

The present invention solves the above-mentioned problems of a nonaqueous electrolyte battery provided with a positive electrode capable of reversibly occluding and discharging Li ⁺ by charging and discharging and a carbon negative electrode. An object is to improve charge / discharge cycle characteristics.

[0010]

According to the present invention, there is provided a positive electrode including a positive electrode active material capable of releasing and occluding lithium ions upon charging and discharging;
The addition of one type or a mixture of multiple types of fluorocarbon to the negative electrode of a non-aqueous electrolyte secondary battery including a negative electrode containing carbon capable of inserting and extracting lithium ions by charge and discharge and a non-aqueous electrolyte. It is a feature.

In the present invention, since the reaction amount of Li ⁺ with respect to the volume of the additive is larger than that of carbon, the decrease in the amount of the positive electrode active material due to the addition of the additive to the negative electrode is minimized.
Precipitation of lithium on the negative electrode due to charging can be suppressed, and a battery with high energy density and good cycle characteristics can be realized.

Further, the conductivity of the negative electrode is improved by the carbon generated by the reaction between the additive and Li ^+, and the charge and discharge characteristics of the battery can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is to add carbon fluoride to a negative electrode for the purpose of consuming the irreversible capacity of the positive electrode.
Here, fluorocarbon is a fluorinated carbonaceous material and is represented by the general formula (C _x F) _n . Representative of them are (CF) _n and (C ₂ F) _n, which are generally known as positive electrode active materials for lithium primary batteries. Hereinafter, the present invention will be described by expressing a single substance or a mixture of these fluorocarbons as (C _x F) _n .

First, it is generally known that fluorocarbon and Li ⁺ undergo an irreversible electrochemical reaction as shown in Chemical formula 1 in a non-aqueous electrolyte.

[0015]

Embedded image (C _x F) _n + nLi ⁺ + ne ⁻ → nxC + nLi
F This reaction is performed with respect to a reference electrode using lithium metal.
In the present invention, Li ⁺ released from the positive electrode during the first charge of the battery was added to the negative electrode (C _x
F) Reacts with _n . As a result, L for the irreversible capacity of the positive electrode
i ⁺ is fixed to the negative electrode as irreversible LiF in the first cycle of charging, and is not released from the negative electrode in the second and subsequent cycles of discharging. Further, carbon generated by the reaction of Chemical Formula 1 in the negative electrode plate improves the conductivity in the negative electrode plate, so that the resistance polarization of the negative electrode can be reduced. Further, this carbon contributes to the insertion and extraction of Li ⁺ by charging and discharging by a reaction mechanism similar to that of the negative electrode carbon, and thus is effective in increasing the capacity of the battery.

That is, as shown in FIG. 2, when irreversible lithium ions (capacity B in FIG. 2) from the positive electrode are consumed by (C _x F) _n added to the negative electrode, the load on the negative electrode in the charged state is reduced. (C _x F) _n is smaller than that in the case where _n is not added, so that the reversible capacity of the positive electrode and the reversible capacity of the negative electrode can be maximized, and metallic lithium is deposited on the negative electrode by a charge / discharge cycle. Thus, a secondary battery having a larger discharge capacity than before can be realized.

Here, the load of the negative electrode refers to the total amount of reversible and irreversible lithium present in the negative electrode in a charged state, and when this amount increases, the limit of Li + storage is approached and metallic lithium tends to precipitate. According to the present invention, this phenomenon is effectively suppressed.

The additive of the present invention is, for example, (CF)_n,
(C_TwoF)_n, The true density is 2.6, 2.8 g / cc
Because it has a value slightly larger than 2.2 g / cc of carbon,
Compared to the increase in the amount of negative electrode carbon in the conventional method described above,
Lower volume of additive per volume. Furthermore, (C
F)_n, (C_TwoF)_nIs Li⁺That electrochemically reacts with
The electric capacities are 864 and 623 mAh / g, respectively.
Li on carbon⁺Vs. 372 mAh / g of the reaction where
And about 1.7 to 2 times as much Li per weight⁺Reaction volume
One. Further, L is contained in carbon generated by the reaction of the formula [1].
Taking into account the element into which i + is inserted, the irreversible capacity of the positive electrode
The amount of additive required to consume and fix to the negative electrode is
When increasing the amount of negative electrode carbon, the weight and volume of the electrode plate
Can be greatly reduced, and the corresponding positive electrode
Since the amount of active material can be increased, the battery
The capacity can be increased. Of the above, Li⁺Is L
Since the effect of the reaction amount changing to iF is dominant,
It is used as an additive to the negative electrode in the present invention (C_xF)_nIs Li
⁺The reaction electric capacity of the negative electrode carbon is at least Li⁺But
Exceeds 372 mAh / g, which is the amount of electricity for the inserted reaction
The effect of the present invention is remarkably obtained by using
Will be. In other words, (C) as an additive
_xF)_nIs the average x value of Li⁺Reaction capacity with 3
What should be 4.38 or less, which is 72 mAh / g or more
Is calculated. However, in practice (C_xF)_nIs Li ⁺When
Is slightly Li⁺Occlusion of
And the fact that the true density is large, the x value is about
The effect of the present invention is remarkably obtained when the ratio is 4.5 or less.
Was experimentally revealed. The minimum value of x value is (CF)_n
1, which is fully fluorinated (CF)
_nIndicates a composition which is usually slightly excessive in fluorine,
It may indicate an effective value. From these, 0.
It is preferable to use an additive satisfying 9 ≦ x ≦ 4.5.

[0019] The addition amount of the fluorocarbon in the present invention, it is preferable reaction electric capacity of the additive and Li ⁺ are capacity and same capacity approximately by subtracting the negative electrode irreversible capacity from the positive electrode irreversible capacity.

Incidentally, compounds which can occlude or contain Li ⁺ (eg, FeO, FeO ₂ , Fe ₂ O ₃ , SnO, Sn)
O ₂ , MoO ₂ , V ₂ O ₅ , Bi ₂ Sn ₃ O ₉ , WO ₃ , W
O ₂ , Nb ₂ O ₅ : JP-A-7-192723, metal oxides, sulfides, hydroxides, and selenides containing lithium: JP-A-8-213053, transition metal oxides capable of absorbing and releasing lithium in _{Li p Ni q V 1-q} O r, P = 0.
4 to 3, q = 0 to 1, r = 1.2 to 5.5
No. 44972) has been reported.
All of these reports are added for the purpose of improving the stability of the negative electrode characteristics at the end of discharge or overdischarge, and all require reversibility. These additives also have a function of consuming Li + corresponding to the irreversible capacity of the positive electrode at the negative electrode, as in the present invention. The effect of improving the conductivity comparable to the carbon generated by the above reaction of the present invention cannot be obtained, the reaction amount with Li + per volume is small, and in order to improve the cycle characteristics, the battery capacity has to be sacrificed. There was no problem. The present invention can also exert the above-mentioned selected and effective effects on these methods.

Of (C _x F) _n used in the present invention, (C ₂
F) _n is synthesized by fluorinating a carbon material with fluorine gas at 300 to 600 ° C. Further, by this method, (CF) _n can be synthesized by controlling the flow rate of fluorine. Carbon materials such as petroleum coke are also fluorinated by heating at about 100 ° C. with a fluorine compound.

The carbon materials used as raw materials include, for example, thermal black, acetylene black, furnace black, vapor grown carbon fiber, pyrolytic carbon, natural graphite, artificial graphite, mesophase microbeads, petroleum coke, coal coke, Examples include petroleum-based carbon fiber, coal-based carbon fiber, charcoal, activated carbon, glassy carbon, rayon-based carbon fiber, and PAN-based carbon fiber.

In the present invention, the positive electrode active material is, for example, LCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, etc.
Any of the lithium-containing metal compounds that release and occlude i ⁺ can be used, and the charge and discharge efficiency of the first cycle ｛(Li ⁺ occlusion amount by discharge / Li ⁺ release amount by charging) × 100 (% )｝ Is generally in the range of 75-95%.

Among them, LiN is used as a positive electrode active material.
i _x M _1-x O ₂ (M is Co, Mn, Cr, Fe, V, Al
In the case of a lithium-containing nickel oxide represented by any one or more of x, x: 1 ≧ x ≧ 0.5), the charge / discharge efficiency is low, and 75 to 90% for a commonly used material. Applying the present invention when the charge / discharge efficiency is particularly small as described above is most consistent with the purpose of adding the additive of the present invention to minimize the adverse effects caused by the large irreversible capacity of the positive electrode, Particularly, the effect of the present invention is great.

Incidentally, LiNi _x M _1-x O _{2 which is} generally used
As a typical example, for example, a composite hydroxide mainly composed of nickel and lithium hydroxide are mixed, and then mixed at 750 ° C. to 900 ° C.
Some of them were synthesized in a temperature range of ℃ C. When synthesized at a temperature of 750 ° C. or lower, the thermal stability was slightly lowered. On the other hand, when synthesized at a high temperature of 900 ° C. or higher, the charge / discharge efficiency in the first cycle was extremely small. And the discharge characteristics tend to deteriorate.

[0026]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a longitudinal sectional view of the cylindrical battery used in Example 1. In FIG. 3, reference numeral 1 denotes a battery case processed from a stainless steel plate having resistance to organic electrolyte, 2 denotes a sealing plate provided with a safety valve, and 3 denotes an insulating packing. 4 is an electrode group,
A positive electrode plate 5 and a negative electrode plate 6 are spirally wound a plurality of times via a separator 7 and housed in the battery case 1.
From the positive electrode plate 5, an aluminum positive electrode lead 5a is formed.
Is pulled out and connected to the sealing plate 2, and the negative electrode lead 6 a made of nickel is pulled out from the negative electrode plate 6 to
Connected to the bottom of Reference numeral 8 denotes an insulating ring provided on the upper and lower portions of the electrode plate group 4, respectively.

Next, a method for synthesizing the positive electrode active material will be described. First, a nickel sulfate solution and a cobalt sulfate solution are introduced into a vessel at a constant flow rate, a sodium hydroxide solution is added with sufficient stirring, and the generated precipitate is washed with water and dried to obtain a nickel-cobalt composite hydroxide (Ni _0.85 Co _0.15 (O
H) ₂ ) was obtained. The obtained nickel-cobalt composite hydroxide is mixed with lithium hydroxide, and calcined at 800 ° C. for 10 hours in an oxidizing atmosphere to obtain LiNi _0.85 Co _0.15 O _2.
Was synthesized.

First, the positive electrode plate 5 is made of LiN which is a positive electrode active material.
To 100 parts by weight of i _0.85 Co _0.15 O ₂ powder, 3 parts by weight of acetylene black and 5 parts by weight of a fluororesin binder were mixed and suspended in an N-methylpyrrolidone solution to form a paste. This paste is applied on both sides of an aluminum foil having a thickness of 0.020 mm, and after drying, has a thickness of 0.130 mm and a width of 35 m.
A positive electrode plate 5 having a length of 270 mm was prepared. An aluminum piece was attached as the positive electrode lead 5a.

The positive electrode irreversible capacity of this positive electrode is 20 mAh /
g, and the charge / discharge efficiency was 85%.

The negative electrode plate 6 was prepared by adding (C)
F) After adding 4 parts by weight of _n , a styrene-butadiene rubber-based binder was mixed and suspended in an aqueous solution of carboxymethyl cellulose to form a paste. Note that this (CF)
The addition amount of _n is calculated so that the sum of the electric capacity of (CF) _n and the irreversible capacity of the carbon material is equal to the irreversible capacity of the positive electrode. The (CF) _n used here is a fluorinated product of petroleum coke, and the analysis value of C: F is 0.9: 1 in atomic ratio. Of these, effective fluorine which substantially performs an electrochemical reaction And the ratio of carbon is 1: 1 and (CF)
The electric capacity of _n was calculated from the effective value.

Then, the paste is coated with a thickness of 0.015 mm.
0.2 mm thick and 37 mm wide after drying
A negative electrode plate having a length of 300 mm and a length of 300 mm was prepared.

Then, the positive electrode plate and the negative electrode plate are spirally wound via a separator, and have a diameter of 13.8 mm and a height of 50 m.
m in a battery case.

Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were used as the electrolyte.
A solution prepared by dissolving lithium hexafluorophosphate at a ratio of 1 mol / l in a mixed solvent mixed at a volume ratio of 0:20:50 was injected into the electrode group 4, and then the battery was formed with a sealed opening. The battery was designated as test battery A.

Similarly, EC, diethyl carbonate (DEC) and methyl propionate (MP) were added to the solvent of the electrolyte solution.
A battery using a solvent mixed at a volume ratio of 0:20:50 was used for test battery B, EC, DEC and ethyl propionate (E
A battery using a solvent in which P) was mixed at a volume ratio of 30:20:50 was used as a test battery C, and EC, EMC, DMC, and MP were used in 3 batteries.
Test battery D was prepared using a solvent mixed at a volume ratio of 0: 20: 30: 20.

As comparative examples, batteries were constructed in the same manner as in Examples (test batteries A to D) except that no additive was added to the negative electrode, and batteries E to H were obtained.

Each of the above batteries was charged at 20 ° C. with a charge / discharge current of 100
A charge / discharge cycle was performed at a charge end voltage of 4.2 V at mA and a discharge end voltage of 2.5 V. The number of cycles at which the discharge capacity was reduced to 70% of the discharge capacity at the third cycle was defined as the cycle life.

The irreversible capacity of the positive electrode is a value obtained by subtracting the amount of Li ⁺ that can be stored in the positive electrode in the first cycle of discharge from the amount of Li ⁺ released from the positive electrode in the first cycle of charge. Is the ratio of these ｛(storage / release)
× 100 (%)｝. This measurement test was performed at about 20 ° C. using a metal lithium plate as the negative electrode plate, and preparing a battery by the same manufacturing method as the above test battery A except that the charge / discharge voltage was controlled by the positive electrode potential. . The measurement method is as follows: after performing constant voltage charging (4.2 V / 2.5 hours),
The amount of charge / discharge of the positive electrode plate when a constant current discharge ( ² mA / cm ² ) was performed up to 5 V was measured, and the amount of charge was converted into the amount of release of Li ⁺ or the amount of occlusion.
The irreversible capacity of the negative electrode was about 20 mAh / g, and the charge / discharge efficiency was 92%. For these measurements, a battery was prepared in the same manner as the test battery A described above, except that a metal lithium plate was used in place of the positive electrode plate, and the charge / discharge voltage was controlled by the potential of the carbon negative electrode. The measurement was performed in the same manner as in the case of the positive electrode. However, the charging in this case is constant voltage charging (0
V / 2.5 hours), the discharge was performed up to 0.5 V, and the irreversible capacity and charge / discharge efficiency of the negative electrode were calculated from the charge / discharge capacity at that time.

The charge, discharge capacity and terminal cycle of the first cycle of these batteries are shown in Table 1.

[0040]

[Table 1]

It can be seen that the difference between the charge capacity and the discharge capacity in the first cycle in the batteries of the example and the comparative example is almost the same in each battery.

This indicates that the discharge capacity of the battery is determined by the reversible capacity of the positive electrode in each case.

However, when the charge / discharge cycle of these batteries is continuously performed, the cycle characteristics of the battery of the present invention to which the additive is added are remarkably improved as compared with the battery of the comparative example to which no additive is added. You can see that.

As a result of disassembling and observing the battery after the cycle test, deposition of lithium metal having a metallic luster was observed on the negative electrode surface of the battery of the comparative example, and no deposition was observed in the battery of the example.

From these results, in the comparative example, even when the battery capacity at the beginning of the cycle was the same as that of the example, the charge / discharge was performed with the irreversible capacity of the positive electrode (capacity A in FIG. 1) remaining in the carbon of the negative electrode. As the cycle proceeds, the substantial reversible capacity decreased, and the charge was performed beyond the reversible charge / discharge capacity of the negative electrode due to charging, so metallic lithium was deposited on the negative electrode plate surface and the discharge capacity was considered to have decreased significantly. Can be By the way,
In the case of the comparative example, a battery with good cycle characteristics can be realized by reducing the amount of the positive electrode active material or lowering the charging voltage to allow a margin for the reversible capacity of the negative electrode.
Since the discharge capacity itself is small, it is not possible to realize a high capacity battery.

On the other hand, the battery of the present invention consumes (CF) _n (capacity B in FIG. 2) to which a capacity not involved in charge / discharge was added, which corresponds to A in FIG. A battery with maximum reversible capacity and good cycle characteristics can be obtained.

Also, batteries using other mixed solvents (B,
Even in cases C and D), the cycle characteristics are superior to those of the battery of the comparative example.

Example 2 As Example 2, the amount of (CF) _n added to the negative electrode was 0.05,
Test batteries I, J, K, and L were prepared under the same conditions as the test battery A of Example 1 except that the amounts were 1, 4, 6, and 10 parts by weight, and the charge / discharge cycle was performed under the same conditions as in Example 1. The test was performed. The analytical value of (CF) _n is represented by an atomic ratio of C: F =
0.9: 1. (Table 2) shows the test battery A of Example 1.
And test results of the test batteries (I to L) of Example 2 and the battery of Comparative Example (E).

[0049]

[Table 2]

In any of the batteries of the second embodiment, the charge capacity in the first cycle does not show a large change depending on the battery as in the case of the first embodiment. However, the discharge capacity in the first cycle of the battery to which (CF) _n was added in an amount of 6 parts by weight or more was smaller than the discharge capacity of the other batteries. Li this calculated value mentioned in the Examples 1, i.e. was added in excess with respect to the addition amount of (CF) _n of 4 parts by weight (CF) _n, corresponding to a part of the reversible capacity of the positive electrode ^Probably because it reacted with ⁺ .

The cycle characteristics of each battery are (C
F) In the case of adding 0.05 parts by weight of _n , since all of the Li ^{+ for} the positive electrode irreversible capacity is not consumed by the additive, a part is occluded in the carbon of the negative electrode, and the part is substantially irreversible. Because of the capacity, the effect of improving the cycle characteristics is not remarkably recognized. However, compared to the comparative example in which no additive is added, even with such a small amount of addition, the adverse effect is reduced, and thus the cycle characteristics are improved.

On the other hand, in the battery containing 6 parts by weight of (CF) _n , although the reversible capacity itself of the positive electrode was partially consumed by (CF) _n , the discharge capacity was slightly reduced. Is shown.

When 10 parts by weight of (CF) _n is added, the capacity of the battery is greatly reduced, but the cycle characteristics are excellent.

From the above, it is preferable that the additive amount when (CF) _n alone is used as the additive is 0.5 to 6 parts by weight based on 100 parts by weight of the carbon material of the negative electrode.

Example 3 As Example 3, (C
F) _n , (C ₂ F) _n , (C ₄ F) _n , and (C ₆ F) _n singly or by changing the mixing ratio, and the average x value of (C _x F) _n is the analytical value. Various batteries were prepared under the same conditions as the test battery A of Example 1 except that they were prepared so as to be 0.9, 4, 4.5, and 6 and used as an additive. A charge / discharge cycle test was performed.

Table 3 shows the test results of the batteries of Example 3 and Comparative Example.

[0057]

[Table 3]

From the results of Example 3, it can be seen that when the value of x increases when the amount of addition is constant (4 parts by weight), the additive cannot consume all the irreversible capacity of the positive electrode.
The results show that the cycle characteristics are slightly inferior to those having a value of 4.5 or less. That is, x = 0.9 when (CF) _n is used alone, and x when (C ₄ F) _n is mainly used
= 4, 4.5, the discharge capacity and the cycle characteristics were almost equally excellent, and the effect of the present invention was remarkably obtained.
On the other hand, when the content of F is lower than these, when x = 6, the cycle characteristics are better than when no additive is used, but the effect of the present invention is not necessarily sufficient.

Further, x = 4 having (C ₄ F) _n as a main component.
In the case of the additive of (c), the amount of reaction with Li ⁺ per weight is small and in order to sufficiently consume the irreversible capacity of the positive electrode, (C
It is necessary to increase the addition amount as compared with the case where an additive mainly comprising F) _n or (C ₂ F) _n is used. However, if it is added excessively, it becomes necessary to greatly reduce the carbon amount of the negative electrode, and the battery capacity becomes small. The limit is 18 parts by weight, and when 20 parts by weight is added, it becomes excessive and the cycle characteristics can be improved but the discharge capacity has to be sacrificed. For this reason (C ₄
F) When only _n is added, the addition amount is desirably 18% or less.

From the above, (C)
_xF ) When _n is added alone or as a mixture, it has been experimentally confirmed that the average value of x of the additive is preferably 0.9 ≦ x ≦ 4.5. It was confirmed that there was an appropriate amount of addition corresponding to the value. For example, when the x value was around 4, it was confirmed that the amount was preferably 18 parts by weight or less.

In the examples, LiN was used as the positive electrode active material.
i _x M _1-x O ₂ (M is Co, Mn, Cr, Fe, V, Al
And any one of x, x: 1 ≧ x ≧ 0.5), a representative material was used. However, the positive electrode active material of the battery to which the present invention is applied is not limited thereto, and Mn, Co, F
e, such as a lithium-containing oxide of a metal mainly composed of Ni,
The present invention can be widely applied to a case where a positive electrode active material that releases and occludes lithium ions by charge and discharge is used. Particularly, a large effect is obtained when a positive electrode active material having a charge and discharge efficiency in the range of 75 to 95% is used.

In the examples, ethylene carbonate was used as one kind of solvent and cyclic carbonate, but other cyclic carbonates such as propylene carbonate and butylene carbonate may be used. Although used, other chain carbonates, such as dipropyl carbonate, propyl methyl carbonate, propyl ethyl carbonate, and the like, may be used.

Although methyl propionate and ethyl propionate have been used as the aliphatic carboxylic acid esters, other aliphatic carboxylic acid esters such as methyl butyrate and ethyl butyrate may be used.

Further, if necessary, solvents such as ethers and lactones can be appropriately mixed.

In the above embodiment, lithium hexafluorophosphate was used as the electrolyte. However, other lithium-containing salts such as lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and hexafluoride were used. Similar effects were obtained with lithium arsenate and the like. Further, the present invention can be widely applied to batteries using a solution other than the above in which a lithium salt is dissolved in an organic solvent as an electrolytic solution.

In the above embodiment, the evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape is different, such as a square battery.

[0067]

As is apparent from the above description, by adding carbon fluoride to a negative electrode mainly composed of a carbonaceous material capable of inserting and extracting lithium ions by charging and discharging, a non-electrode having a high capacity and excellent cycle characteristics is obtained. A water electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a first charge / discharge of a lithium secondary battery when the present invention is not applied.

FIG. 2 is a conceptual diagram of the first charge / discharge of the lithium secondary battery of the present invention.

FIG. 3 is a longitudinal sectional view of a cylindrical battery in the present example and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulating packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Insulating ring

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shoichiro Watanabe 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode including a positive electrode active material capable of storing and releasing lithium ions during charge and discharge, a negative electrode including carbon capable of storing and releasing lithium ions during charge and discharge, and a non-aqueous electrolyte.
A non-aqueous electrolyte secondary battery in which one or more of fluorocarbon is added to the negative electrode. 2. The composition according to claim 1, wherein, when x represents an average atomic ratio of carbon to fluorine in the fluorocarbon alone added to the negative electrode or a mixture thereof, 0.9 ≦ x ≦ 4.5. Non-aqueous electrolyte secondary battery. 3. The method according to claim 1, wherein the positive electrode active material is LiNi _x M _{1 -x} O ₂ (M
Is a lithium-containing nickel oxide represented by the following formula: x, wherein at least one of Co, Mn, Cr, Fe, V, and Al. battery.