JP2001202999A - Charge and discharge method for nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic secondary battery having a superior cycle characteristics, superior reliability and high energy density. SOLUTION: The nonaqueous electrolytic secondary battery consists of a positive pole capable of occluding and emitting lithium and a negative pole comprising a lithium-contained complex nitride expressed by general formula Li(3.0-x)-yMxN (where M is at least one kind of transition metals selected from a group of Co, Mn, Ni and Cu, 0.2<=x<=0.6). The variable y showing a variation of the Li content to be caused following the charge and discharge is to be within the range of -x<y<2.0-x, when charge and discharge are proceeded with.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a method for charging and discharging a lithium secondary battery using a lithium-containing composite nitride as a negative electrode material.

[0002]

2. Description of the Related Art Initially, the use of high-capacity lithium metal as a negative electrode material for non-aqueous electrolyte secondary batteries was actively studied. However, dendrite-like precipitation occurred on the negative electrode during charging, and charging and discharging were repeated. In such a case, there is a possibility that the precipitates may break through the separator and reach the positive electrode side to cause an internal short circuit. For these reasons, it has been difficult to commercialize a non-aqueous electrolyte secondary battery using lithium metal as a negative electrode material from the viewpoint of low reliability and short cycle life. On the other hand, a lithium ion secondary battery using a carbon material as a negative electrode material and a lithium-containing composite oxide as a positive electrode material has been developed as a nonaqueous electrolyte secondary battery. This has a higher voltage and energy density than a secondary battery of an aqueous solution type, has excellent low-temperature characteristics, and has excellent cycle stability because no lithium metal is used for the negative electrode. Was. Normally, since metallic lithium does not precipitate on the carbon material negative electrode, there is no problem of internal short circuit due to dendrite. However, the theoretical capacity of graphite, one of the carbon materials, is 372 mA.
h / g, which is as small as about 1/10 of the theoretical capacity of lithium metal alone.

As another negative electrode material, a nitride containing lithium is known as a high capacity material. The technology of using a lithium-containing composite nitride as a negative electrode material of a battery is relatively new. For example, a lithium nitride metal compound (same as lithium-containing composite nitride) used as an electrode material of an electrochemical element is disclosed in Japanese Patent Application Laid-Open No. 7-78609. Is disclosed.
Among the lithium-containing composite nitrides, a composite nitride of lithium and a transition metal, a general formula Li _{(3.0-x) -y} M _x N (M is Co, M
The compound represented by at least one transition metal selected from the group consisting of n, Ni, and Cu) does not deposit metallic lithium in potential, and therefore does not have a problem of internal short circuit due to dendrites. A compound having a value of about 0.1 to 0.6 has a reversible capacity of 500 to 800 mAh / g.
All are promising negative electrode materials larger than the theoretical capacity of graphite.

However, when the lithium-containing composite nitride as described above is used as a negative electrode material in a battery, there are the following problems. That is, the lithium-containing composite nitride has insufficient charge / discharge cycle characteristics as compared with the carbon anode material. It is presumed that the reason for this is that the volume change due to expansion and contraction in charge and discharge increases as the reversible charge and discharge capacity increases. When the volume difference between charge and discharge is large, large strain is generated, cracks are generated and the nitride particles themselves are fined, and electronic conduction network including entanglement with the conductive agent in the electrode plate due to expansion and contraction Is considered to be loosened or divided, so that the portion that cannot participate in the electrochemical reaction increases, and the charge / discharge capacity decreases.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems in the case of using a lithium-containing composite nitride which is a negative electrode material having a high capacity and excellent charge-discharge cycle characteristics. An object of the present invention is to provide a method for providing an excellent non-aqueous electrolyte secondary battery having a high energy density.

[0006]

In order to solve the above problems, the present invention provides a positive electrode capable of inserting and extracting lithium and a general formula Li _{(3.0-x) -y} M _x N (M is Co , Mn, Ni
And a nonaqueous electrolyte secondary battery including a negative electrode made of a lithium-containing composite nitride represented by at least one transition metal selected from the group consisting of Y representing the change in Li content that changes with
Is regulated in the range of -x <y <2.0-x to perform charging and discharging.

The present invention focuses on the volume change of a high-capacity lithium-containing composite nitride due to charging and discharging, and controls the transition metal content as described above to suppress the volume change, thereby improving the cycle characteristics. Is to improve. Furthermore, the amount of Li in the lithium-containing composite nitride changes with charge and discharge, but by limiting the change range of the amount of Li at this time, it is intended to avoid the cycle deterioration region and suppress the cycle deterioration. is there. In other words, using a lithium-containing composite nitride of an appropriate composition as the negative electrode material, the volume change is minimized, and the change range of Li is controlled by design conditions such as the positive and negative electrode filling capacity balance and charge / discharge conditions. That is, the cycle degradation region is avoided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a lithium-containing composite nitride having a general formula Li _{(3.0-x) -y} M _x N (M is C
o, Mn, Ni and at least one transition metal selected from the group consisting of Ni and Cu). In this lithium-containing composite nitride, the x value corresponding to the content of the transition metal in the above formula is defined as It is assumed that 0.2 ≦ x ≦ 0.6. And Li associated with charge and discharge in lithium-containing composite nitride when lithium-containing composite nitride is used as a negative electrode material of a battery
Is limited to the range of -x <y <2.0-x. Note that the regulation of the y value is methodologically performed by setting design conditions such as the filling capacity balance and charge / discharge conditions. The lithium-containing composite nitride is a compound in which a transition metal atom is dissolved in lithium nitride Li ₃ N. The x value is determined at the time of synthesis. As a result of an experimental study, the amount that can be replaced is in the range of x ≦ 0.6 (the unreacted transition metal remains even when synthesized so that 0.6 <x). The function as is in the range of 0.1 ≦ x ≦ 0.6. When x <0.1, the material itself has almost no electric conductivity and is close to an insulator, and thus does not function as an electrode.

[0009] Regarding the volume change due to charge and discharge, these lithium-containing composite nitrides become amorphous in the first discharge and do not return to crystalline again in the subsequent charge and discharge. It cannot be caught. However, when the change in the electrode plate thickness accompanying the charge and discharge of the negative electrode composed of the lithium-containing composite nitride is traced, the above-mentioned x value is x <
When the electrode material synthesized in 0.2 is included, a result with a large change rate is obtained. It is considered that such a material basically reduces the crystal distortion because the substituted transition metal changes its valence in response to insertion and extraction of Li during charge and discharge. However, in the region of x <0.2, since the absolute amount of the transition metal is insufficient, the effect of alleviating the strain of the crystal due to the change in valence is weakened, and it is presumed that the expansion and contraction of the crystal is promoted. . That is, 0.2 ≦ x ≦
In the region of 0.6, it is presumed that the valence change of the transition metal relaxes the crystal distortion, so that expansion and contraction are suppressed. Therefore, from the viewpoint of a change in volume, it is effective to use a lithium-containing composite nitride in which the x value in the above-mentioned general formula is in the range of 0.2 ≦ x ≦ 0.6 to improve cycle characteristics.

[0010] Further, the amount of change in Li and the cycle deterioration due to charge and discharge of these lithium-containing composite nitrides synthesized in the range of x ≦ 0.2 ≦ x ≦ 0.6 were examined.
In the charging direction, the total amount of Li in the lithium-containing composite nitride Li _{(3.0-x) -y} M _x N is 3.0 or more, that is, 3.0 ≦ (3.0-x) − regardless of the x value. When charge / discharge using the y region was performed, remarkable cycle deterioration was shown. As a result of the examination, it was found that the cause was Li deposition. Therefore,
The region of (3.0-x) -y <3.0, that is, -x <y
It is desirable to perform charge / discharge in the range described above. Next, in the discharge direction, the lithium-containing composite nitride Li
_(3.0-x) the total amount of Li in the _-y M _x N is 1.0 or less, that showed (3.0-x) performed when significant cycle deterioration of charge and discharge using the region of -y ≦ 1.0 . As a result of the investigation, it was found that the cause was a compositional collapse of the lithium-containing composite nitride Li _{(3.0-x) -y} M _x N. In particular, it was also found that in this case, the nitride was decomposed to generate nitrogen gas. Therefore,
1.0 <(3.0-x) -y region, that is, y <2.
It is desirable to perform charging and discharging in the range of 0-x. As described above, the region where -x <y and y <2.0-x, that is, L due to charging and discharging when used as an electrode material of a battery.
It is desirable that y corresponding to the change amount of i be in the range of -x <y <2.0-x.

A further preferred embodiment of the present invention will be described below. Since the lithium-containing composite nitride of the negative electrode has high reactivity with moisture and is deteriorated by moisture, it is preferable to use a highly dehydrated solvent for forming a paste in the electrode manufacturing process. The positive electrode and the negative electrode used in the present invention are obtained by applying a mixture layer containing a conductive agent and a polymer material to a surface of a current collector on a positive electrode material or a negative electrode material capable of electrochemically and reversibly inserting and releasing lithium ions. Can be manufactured.

The conductive agent for the negative electrode used in the present invention may be any material as long as it is an electron conductive material. For example, graphites such as natural graphite (flaky graphite etc.), artificial graphite, expanded graphite, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fibers, Conductive fibers such as metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be included alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black and carbon fiber are particularly preferred. The amount of the conductive agent to be added is not particularly limited.
It is preferably 0% by weight, and particularly preferably 1 to 30% by weight.
Further, since the negative electrode material of the present invention itself has electronic conductivity, it is possible to function as a battery without adding a conductive agent. The current collector for the negative electrode used in the present invention may be any electronic conductor that does not cause a chemical change in the configured battery. For example, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium is used. Particularly, copper or a copper alloy is preferable. In addition, it is desirable to make the current collector surface uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

As the positive electrode material used in the present invention, a lithium-containing transition metal oxide can be used. For example,
Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x C
o _y Ni _1-y O ₂ , Li _x Co _y M _1-y O _z , Li _x Ni _{1- y My}
O _z , Li _x Mn ₂ O ₄ , Li _x Mn _{2- y My} O ₄ (M = Na,
Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Z
at least one of n, Al, Cr, Pb, Sb and B, x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to
2.3). Here, the above-mentioned x value is a value before the start of charge / discharge, and increases / decreases due to charge / discharge. When a positive electrode material such as a lithium-containing transition metal compound that starts from normal charging (from the direction of Li release) is used, since the nitride material of the present invention is a negative electrode material that normally starts from discharging, In addition, a chemical conversion treatment for removing Li in advance from one of the positive and negative electrodes is required. It is also possible to use other positive electrode materials such as transition metal chalcogenides, lithium compounds of vanadium oxides, lithium compounds of niobium oxides, conjugated polymers using organic conductive substances, and Chevrel phase compounds. Manganese dioxide,
In the case of a positive electrode material such as vanadium pentoxide starting from normal discharge, it is not necessary to perform a chemical conversion treatment, which is advantageous in production. It is also possible to use a mixture of a plurality of different positive electrode materials. The average particle size of the particles of the positive electrode material is not particularly limited, but is preferably 1 to 30 μm.

The conductive agent for the positive electrode used in the present invention may be any electronic conductive material which does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, graphites such as natural graphite (flaky graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black,
Carbon blacks such as thermal black, carbon fiber,
Conductive fibers such as metal fibers, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives alone. Alternatively, they can be included as a mixture thereof. Among these conductive agents, artificial graphite and acetylene black are particularly preferred. The addition amount of the conductive agent is not particularly limited, but is preferably 1 to 50% by weight, and particularly preferably 1 to 30% by weight based on the positive electrode material. For carbon and graphite, 2 to 15% by weight is particularly preferred. The positive electrode current collector used in the present invention may be any electronic conductor that does not cause a chemical change in the charge and discharge potential of the positive electrode material used. For example, in addition to stainless steel, aluminum, titanium, carbon, conductive resin, and the like, a material obtained by treating the surface of aluminum or stainless steel with carbon or titanium is used. Particularly, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. In addition, it is desirable to make the current collector surface uneven by surface treatment. As the shape, in addition to a foil, a film, a sheet, a net, a punched material, a lath body, a porous body, a foamed body, a fiber group, a molded body of a nonwoven fabric body, or the like is used. The thickness is not particularly limited,
Those having a thickness of 1 to 500 μm are used.

As the binder for the positive and negative electrodes, for example,
For example, polyethylene, polypropylene, polytetrafluoro
Ethylene, polyvinylidene fluoride, styrene butadiene
Rubber, tetrafluoroethylene-hexafluoroethyl
Len copolymer, tetrafluoroethylene-hexafluoro
Propylene copolymer, tetrafluoroethylene-per
Fluoroalkyl vinyl ether copolymer, vinyl fluoride
Riden-hexafluoropropylene copolymer, vinyl fluoride
Nilidene-chlorotrifluoroethylene copolymer, ethyl
Len-tetrafluoroethylene copolymer, polychloroto
Trifluoroethylene, vinylidene fluoride-pentafluor
Propylene copolymer, propylene-tetrafluoroe
Tylene copolymer, ethylene-chlorotrifluoroethylene
Copolymer, vinylidene fluoride-hexafluoropropyl
Len-tetrafluoroethylene copolymer, vinylidene fluoride
Den-perfluoromethyl vinyl ether-tetrafur
Oroethylene copolymer, ethylene-acrylic acid copolymer
Or (Na⁺) Ion crosslinked product, ethylene-
Methacrylic acid copolymer or (Na⁺) Io
Crosslinked product, ethylene-methyl acrylate copolymer or
(Na⁺) Ion crosslinked product, ethylene-methac
Methyl acrylate copolymer or (Na ⁺) Io
These materials can be used alone or
It can be used as a mixture.

The structure of the negative electrode plate and the positive electrode plate in the present invention is as follows.
It is preferable that at least the negative electrode mixture surface is opposed to the positive electrode mixture surface. The non-aqueous electrolyte of the present invention, a solvent,
And a lithium salt dissolved in the solvent. For example, ethylene carbonate, propylene carbonate,
Cyclic carbonates such as butylene carbonate and vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and dipropyl carbonate; aliphatic carboxylic acids such as methyl formate, methyl acetate, methyl propionate, methyl propionate and ethyl propionate Esters, γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane, 1,
Chain ethers such as 2-diethoxyethane and ethoxymethoxyethane, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, dimethylformamide, dioxolan, acetonitrile, propyl nitrile , Nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane,
1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,
Examples include aprotic organic solvents such as 3-propanesultone, anisole, dimethylsulfoxide, and N-methylpyrrolidone, and one or more of these can be used in combination. Among them, a mixed system of a cyclic carbonate and a chain carbonate or a mixed system of a cyclic carbonate, a chain carbonate and an aliphatic carboxylic acid ester is preferable.

Examples of the lithium salt dissolved in these solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiPF
AlCl ₄ , LiSbF ₆ , LiSCN, LiCl, Li
CF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ ,
LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ C
l ₁₀ , lithium lower aliphatic carboxylate, LiCl, Li
Br, LiI, chloroborane lithium, there may be mentioned lithium tetraphenylborate, and imides like, can be used alone or in combination of two or more in the electrolyte solution or the like to use them, in particular free of LiPF ₆ More preferably. A particularly preferred non-aqueous electrolyte in the present invention is an electrolyte containing at least ethylene carbonate and ethyl methyl carbonate, and containing LiPF ₆ as a supporting salt. The amount of these electrolytes added in the battery is
Although not particularly limited, a necessary amount can be used depending on the amounts of the positive electrode material and the negative electrode material or the size of the battery. The amount of the supporting electrolyte dissolved in the nonaqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / l. In particular, 0.5
More preferably, it is set to と す る 1.5 mol / l. It is also effective to add another compound to the electrolyte for the purpose of improving the discharge and charge / discharge characteristics. For example, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, pyridine, hexaphosphoric triamide, nitrobenzene derivative, crown ethers, quaternary ammonium salt, ethylene glycol dialkyl ether and the like can be mentioned. The shape of the battery can be any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, and a large type used for electric vehicles. In addition, the nonaqueous electrolyte secondary battery of the present invention can be used for portable information terminals, portable electronic devices, home small power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like, but is not particularly limited thereto. Not necessarily.

[0018]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

Example 1 Method for Synthesizing Negative Electrode Material A predetermined amount of lithium nitride and a transition metal powder were mixed, placed in a porcelain crucible, and heated at 700 ° C. for 8 hours in a nitrogen atmosphere to obtain a lithium-containing composite nitride. . Since the target compound in which the transition metal was dissolved in lithium nitride was obtained as a solidified product, the solidified product was pulverized with a ball mill and classified with a sieve to obtain particles having a size of 45 μm or less. In this embodiment,
Co was used as a transition metal, and the above x was used as a comparative sample.
Six types of lithium-containing composite nitrides having values of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were synthesized, respectively.

FIG. 1 is a cross-sectional view of a button-type battery manufactured as a test cell for comparing and examining the cycle characteristics of the non-aqueous electrolyte secondary battery according to the present invention. In FIG. 1, 1
Is a sealing plate made of stainless steel, and a nickel mesh 2 is fixed to the inner surface thereof by resistance welding. The negative electrode 3 including the lithium-containing composite nitride is formed on the copper foil 4, and has a structure in which current is collected by pressing the copper foil 4 and the nickel mesh 2. Positive electrode 6 using LiCoO ₂ as positive electrode material
Is an electrode formed on the aluminum foil 7 and punched out in a disk shape. The positive electrode case 8 made of stainless steel has a stainless steel net 9 fixed to the inner surface by resistance welding. The positive electrode 6 is formed integrally with the aluminum foil 7, and has a structure in which the aluminum foil 7 is collected by pressing a stainless steel mesh 9.
After placing a porous separator 5 made of polyethylene on the positive electrode 6 and injecting an organic electrolyte, the sealing plate 1 is combined via a gasket 10, and the opening edge of the positive electrode case 8 is bent inward and caulked. The battery contents were hermetically sealed. The organic electrolytic solution is obtained by dissolving 1 mol / liter of LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.

In this embodiment, the lithium-cobalt composite oxide (LiCoO ₂ ) is used as the positive electrode material. However, the lithium-containing composite nitride of the negative electrode is in a so-called Li occlusion state in a charged state at the time of synthesis, and the LiCoO 2 of the positive electrode ₂ also has a so-called Li occlusion state in which the initial state is a discharge state,
A battery cannot be configured as it is. It is necessary to desorb Li from either the positive or negative electrode material and combine the batteries in a Li-released state. Therefore, here, a positive electrode material obtained by extracting Li from the LiCoO ₂ of the positive electrode by acid treatment in advance, and a product equivalent to the composition formula Li _0.5 CoO ₂ were used at the time of manufacturing the battery. Button-type batteries as shown in FIG. 1 were manufactured using Li _0.5 CoO ₂ equivalent material for the positive electrode and six types of nitrides using Co for the transition metal described above for the negative electrode material. Were compared.

FIG. 2 shows a comparison of the cycle characteristics of the above-mentioned button type batteries using lithium-containing composite nitrides having six kinds of x values. For example, x =
0.4, that is, a battery using a lithium-containing composite nitride having a composition of Li _2.6 Co _0.4 N (Li with Li desorbed on the positive electrode)
_0.5 CoO ₂ ), the cathode material is filled with about 0.30 g, and an initial capacity of 42 mAh is obtained. At this time, the filling amount of the lithium-containing composite nitride as the negative electrode material was about 0.06 g. The charge / discharge is 5m
3. A constant current of A is used to set end voltages of charging and discharging.
The test was performed at 1 V and 2.0 V. Also, the cycle is
Confirmed up to 50 cycles. In the case of this battery, the capacity at the 50th cycle was 38 mAh, so the cycle deterioration rate was 0.190% / cycle. The cycle deterioration rate used here is expressed as a percentage obtained by dividing the capacity reduction amount obtained by subtracting the capacity of the 50th cycle 38 mAh from the initial capacity 42 mAh by the initial capacity 42 mAh and the number of cycles 50, and is expressed as a percentage. The capacity reduction rate is based on the initial capacity per cycle.

FIG. 2 clearly shows that cycle reversibility is excellent in the range of 0.2 ≦ x ≦ 0.6. In addition,
The cycle deterioration rate at this time is x = 0.1, 0.2, 0.
0.538%, 0.252% in the batteries using lithium-containing composite nitrides of 3, 0.4, 0.5, and 0.6, respectively.
%, 0.224%, 0.190%, 0.178% and 0.202%.

<< Embodiment 2 >> A button-shaped electronic device similar to Embodiment 1
In the pond, the anode has x = 0.4, that is, Li_2.6Co_0.4N
Battery using lithium-containing composite nitride of composition
Was. In this embodiment, in order to confirm the depth limit in the charging direction,
In the positive electrode, Li with a reduced Li desorption amount is used. _0.7CoO_TwoTo
Using. The filling amounts of the positive and negative electrodes were the same as in Example 1.
They were about 0.3 g and 0.06 g, respectively. This battery configuration
In the case of, the depth of discharge is shallow because the positive electrode is closer to the discharge side.
The cycle reversibility in the discharge direction is rather improved.
However, during charging, the positive electrode is Li_0.5CoO_TwoCan charge up to
As a result, the excess 0.2Li generated due to non-desorption is transferred to the negative electrode.
The lithium-containing composite nitride after charging.
The amount of Li present is Li in the initial state._2.6Co_0.4Value greater than N
It can be. Therefore, changing the charging depth variously,
The charge and discharge cycles were compared.

FIG. 3 shows an apparent composition formula of Li _z Co _0.4 N
(Z is the number of Li in the lithium-containing composite nitride, z = 2.6 when the battery is configured), when the charge depth represented by the z value and the charge / discharge cycle is performed at the charge depth 2 shows the relationship between the cycle deterioration rates. The cycle deterioration rate was obtained from the difference between the initial capacity as in Example 1 and the capacity at the 50th cycle. As is apparent from FIG. 3, the cycle deterioration rate changes abruptly when the z value is 3.0. As a result of disassembling and examining the battery after the cycle test, the deterioration rate deteriorated.
It was found that lithium deposition was observed in the battery of 0 ≦ z. This lithium precipitation is considered to be the cause of cycle deterioration. As a result of a cycle test for increasing the depth of charge using a lithium-containing composite nitride in the range of 0.2 ≦ x ≦ 0.6 excellent in the cycleability specified in Example 1, the cycle deterioration was related to the x value. However, it depends on the amount of Li in the lithium-containing composite nitride, and in any case, Li _3.0 Co _x N (0.2 ≦ x ≦
It was found that when the ratio exceeded 0.6), significant cycle deterioration occurred. From the above results, the Li amount (3.0-x) -y represented by the general formula Li _{(3-x) -y} M _x N during charging is (3.0-x) -y <3. .0, that is, -x <y
It is desirable that

<< Embodiment 3 >> In this embodiment, a button-type battery similar to that of Embodiment 1 is used.
A battery using a lithium-containing composite nitride having a composition of i _2.6 Co _0.4 N was manufactured. In this example, in order to confirm the depth limit in the discharge direction, a battery configuration was used in which Li _0.5 CoO ₂ was used for the positive electrode and the filling amount of the positive electrode was relatively increased.
Li _{0. 5} CoO ₂ loading of the positive electrode and the negative electrode of Li _2.6 Co
_0.4 N loading is about 0.5 g and 0.06 g respectively
And In the case of this battery configuration, the charging depth is the same as in the first embodiment, and there is basically no problem with the cycle reversibility in the charging direction. Further, the depth in the discharge direction can be arbitrarily set by cutting with the discharge capacity. In particular, since the filling amount of the positive electrode is relatively increased, there is a margin in the discharge capacity of the positive electrode, and it is possible to discharge the negative electrode deeply. Therefore,
Charge / discharge cycles were compared with various discharge depths.

FIG. 4 shows the apparent composition formula of Li _z Co _0.4 N
(Z is the number of Li in the lithium-containing composite nitride, z = 2.6 when the battery is configured) and the discharge depth expressed by the z value and the charge / discharge cycle at that discharge depth 2 shows the relationship between the cycle deterioration rates. The cycle deterioration rate was obtained from the difference between the initial capacity as in Example 1 and the capacity at the 50th cycle. As is clear from FIG. 4, the cycle deterioration rate changes abruptly when the z value is 1.0. In addition, it was found that the battery that had been cycled with the depth of discharge being z ≦ 1.0 had swollen after the cycle test. As a result of disassembling and examining the battery, it was found that gas had accumulated in the battery. Further, when this gas was analyzed, it was found that most of the gas was nitrogen gas.

Since the nitrogen component in this battery system cannot be considered other than nitrogen in the nitride of the negative electrode, it is assumed that this gas was generated by decomposition of the lithium-containing composite nitride of the negative electrode material. Is done. In particular, withdrawing Li from the negative electrode by discharging is creating a cation-deficient state, and in such a situation where the charge balance of cations and anions in the lithium-containing composite nitride is greatly lost, the anion component That is, it is logical that the reaction proceeds in a direction to release nitrogen. As a result of a cycle test in which the depth of discharge was increased using a lithium-containing composite nitride in the range of 0.2 ≦ x ≦ 0.6 excellent in the cycleability specified in Example 1, the cycle deterioration was related to the x value. However, it depends on the amount of Li in the lithium-containing composite nitride, and the discharge depth is Li _1.0 Co _x N (0.2 ≦ x
≦ 0.6), significant cycle deterioration was found to occur. From the above results, the general formula Li _{(3-x) -y} M _x N
The Li amount (3.0-x) -y represented by is 1.0 <(3.0-x) -y at the time of discharge, that is, y <
2.0-x is desirable.

In the above embodiment, Co was used as a transition metal species to be substituted. However, the same phenomenon and similar phenomenon occur when Mn, Ni or Cu is used instead of Co, and when they are used in combination. The effect was obtained.

[0030]

As described above, according to the present invention, a high energy density non-aqueous electrolyte secondary battery having excellent cycle characteristics and reliability can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery in one embodiment of the present invention.

FIG. 2 is a diagram comparing cycle characteristics of batteries using Li _{(3-x) -y} M _x N having different x values for a negative electrode.

FIG. 3 is a diagram showing the relationship between the z value of Li _z Co _0.4 N used for the negative electrode and the cycle deterioration rate.

FIG. 4 shows Li _z Co _0.4 used for a negative electrode in another example.
It is a figure showing the relation between the z value of N and the cycle deterioration rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sealing plate 2 Nickel net 3 Negative electrode 4 Copper foil 5 Separator 6 Positive electrode 7 Aluminum foil 8 Positive electrode case 9 Stainless steel net 10 Gasket

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaki Hasegawa 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery Industry Co., Ltd. (72) Inventor Shuji Tsutsumi 1-1, Matsushita-cho, Moriguchi-shi, Osaka Matsushita Battery (72) Inventor Yoji Sakurai 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Sou Arai 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5H003 AA04 BB04 BD03 5H014 AA02 EE10 HH01 5H029 AJ05 AK03 AL01 AM02 AM03 AM04 AM05 AM07 BJ03 CJ16 HJ02 5H030 AA00 AS20 FF51

Claims (1)

[Claims] A positive electrode capable of inserting and extracting lithium;
General formula Li _{(3.0-x) -y} M _x N (M is at least one transition metal selected from the group consisting of Co, Mn, Ni and Cu, 0.2 ≦ x ≦ 0.6) A non-aqueous electrolyte secondary battery including a negative electrode made of lithium-containing composite nitride,
The variable y representing the change in the Li content that changes with charge and discharge is-
A charging / discharging method for a non-aqueous electrolyte secondary battery, wherein charging / discharging is performed in a range of x <y <2.0-x.