JP2010102841A - Nonaqueous electrolyte lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte lithium-ion secondary battery having a high energy density, in which reduction of energy density by irreversible capacity in initial charge and discharge is minimized by using a high-capacity positive electrode. <P>SOLUTION: As a positive electrode active material 4 which is consumed by the initial irreversible capacity specific to a negative electrode active material 1 including at least one selected from Si, Si oxide and C, a lithium-containing composite nitride represented by the higher capacity formula: Li<SB>3-x</SB>M<SB>x</SB>N (M is one or more transition metals selected from Co, Ni and Cu, and x is 0≤x≤0.8) is used to reduce the weight of the positive electrode active material 4 which is not used for charge and discharge after the initial discharge, whereby the nonaqueous electrolyte lithium-ion secondary battery having a high energy density is obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte lithium ion secondary battery using a high-capacity active material for a positive electrode and having a high energy density.

  Currently, with the spread of mobile devices such as mobile phones and notebook personal computers, the role of secondary batteries as the power source is regarded as important. These secondary batteries are small, lightweight, and have a high capacity, and are required to have a performance that does not easily deteriorate even after repeated charging and discharging. Currently, lithium ion secondary batteries are most frequently used.

  Carbon (C) such as graphite or hard carbon is mainly used for the negative electrode of the lithium ion secondary battery. Although C can repeat charge / discharge cycles satisfactorily, the capacity has already been used up to the vicinity of the theoretical capacity. On the other hand, there is a strong demand for increasing the capacity of lithium ion secondary batteries, and negative electrode materials having a higher capacity than carbon, that is, a higher energy density are being studied.

  An example of a negative electrode material capable of realizing a high energy density is silicon (Si). Non-patent document 1 describes that it is actually used as a negative electrode active material.

  Although the negative electrode using Si has a large amount of occlusion and release of lithium ions per unit volume and a high capacity, pulverization progresses due to large expansion and contraction of the electrode active material itself when lithium ions are occluded and released. And the irreversible capacity | capacitance in first time charging / discharging is large, and the part which is not utilized for charging / discharging is made in the positive electrode side. Moreover, there is a problem that the charge / discharge cycle life is short.

  Patent Document 1 proposes a method of using Si oxide as a negative electrode active material as a measure for reducing the initial irreversible capacity using Si and improving the charge / discharge cycle life. In Patent Document 1, since the volume expansion / contraction per unit weight of the active material can be reduced by using Si oxide as the active material, improvement in cycle characteristics has been confirmed. On the other hand, since the conductivity of the oxide is low, the current collecting property is lowered, and the irreversible capacity in charge / discharge is large.

  Furthermore, as a countermeasure for improving capacity and charge / discharge cycle life, Patent Document 2 proposes a method using particles obtained by combining a carbon material with Si and Si oxide as an active material. Although the improvement of the cycle characteristics was confirmed by this, it is still insufficient, and the improvement of the first charge / discharge efficiency is insufficient.

  As countermeasures for this initial irreversible capacity, an electrode formation method in which the irreversible capacity is electrochemically charged in advance or a method of making up for the irreversible capacity by attaching metallic lithium to the negative electrode has been attempted.

  The electrode formation method is excellent in that the amount of electricity according to the purpose can be formed by controlling the amount of electricity supplied. However, since the electrode is once charged and then reassembled as a battery, it is cumbersome and productivity is extremely poor.

  The lithium metal sticking method automatically moves Li between an oxide in a short-circuited state and lithium metal by injecting an electrolytic solution. However, in the case of this method, depending on the electrode plate form, there is a problem in quality such that Li migration is insufficient and metallic lithium remains, causing variations in characteristics and problems in safety.

In addition, as a countermeasure for this first irreversible capacity, a lithium-containing composite represented by Si oxide and a general formula Li _3-x M _x N (M is a transition metal, 0 ≦ x ≦ 0.8) is used as a negative electrode. Patent Document 3 proposes a non-aqueous electrolyte lithium ion secondary battery using a mixed active material with nitride. The lithium-containing composite nitride is excellent in terms of compensating the irreversible capacity of the Si oxide. However, the lithium-containing composite nitride has a capacity per weight of about 800 mAh / g, which is small compared to the Si oxide, and only the Si oxide is used. There is a problem that the energy density of the battery is smaller than the energy density of the battery when used as the negative electrode active material.

  The use of Si as a negative electrode material capable of realizing a high energy density increases the energy density of the battery, but the positive electrode occupies a larger proportion of the weight of the entire battery, and a higher capacity on the positive electrode side is also required.

Japanese Patent No. 2999741 JP 2004-139886 A JP 2000-164207 A Li et al., 4 others, A High Capacity Nano-Si Composite Anode Material for Lithium Rechargeable Batteries, Electrochemical and Solid-State Letters, Vol. 49, Vol. 99, Vol.

  As described above, in the prior art, the irreversible capacity in the first charge / discharge is large, there is a portion that is not used for charge / discharge on the positive electrode side, the problem that the charge / discharge cycle life is short, the irreversible capacity in charge / discharge is large. There were problems such as quality problems such as the occurrence of characteristic variations and safety problems, and the problem of low energy density.

  The present invention has been made to solve such problems, and its purpose is to use a high-capacity positive electrode to achieve a high energy density that minimizes a decrease in energy density due to irreversible capacity during initial charge and discharge. An object of the present invention is to provide a non-aqueous electrolyte lithium ion secondary battery.

In order to solve the above problems, the present invention provides a high capacity positive electrode,
Non-aqueous system including lithium-containing composite nitride represented by the general formula Li _3-x M _x N (M is one or more transition metals selected from Co, Ni and Cu, and 0 ≦ x ≦ 0.8) The electrolyte is a lithium ion secondary battery. As x, 0 ≦ x ≦ 0.5 is more preferable, and a more preferable range is 0.4 ≦ x ≦ 0.5.

In addition, at least one selected from Si, Si oxide and C capable of occluding and releasing lithium in the negative electrode active material using the lithium-containing composite nitride and the oxide capable of occluding and releasing lithium as the positive electrode active material. The non-aqueous electrolyte lithium ion secondary battery includes a mixed active material composed of more than seeds. Examples of the Si oxide include silicon dioxide (SiO ₂ ).

  The charge / discharge capacity per unit weight of the oxide capable of occluding and releasing lithium contained in the positive electrode active material is A, the Li discharge potential is A ′, and the charge / discharge capacity per unit weight of the lithium-containing composite nitride is When the B and Li emission potentials are B ′, the nonaqueous electrolyte lithium ion secondary battery satisfies A <B and A ′> B ′.

  When the amount of Li corresponding to the first irreversible capacity of the negative electrode active material is α and the amount of Li released by the lithium-containing composite nitride at the time of initial charge is γ, the weight ratio of the negative electrode active material and the lithium-containing composite nitride is The non-aqueous electrolyte lithium ion secondary battery is selected so as to satisfy α ≧ γ. This reduces the weight of the positive electrode active material used for the irreversible capacity. Therefore, the energy density of the battery increases.

  When the initial charge capacity of the negative electrode active material is Y and the sum of the initial charge capacities of the oxide capable of occluding and releasing lithium and the lithium-containing composite nitride is Z, the relationship is Z ≦ Y. Next battery. Thereby, all the active materials in a positive electrode are used for charging / discharging, and a high energy density is realizable.

Examples of the oxide capable of occluding and releasing lithium include lithium nickelate, lithium manganate, and lithium cobaltate. In addition, in the active material layer of the negative electrode, carbon black, acetylene black, or the like may be mixed in order to impart conductivity as necessary. The electrode density of the produced negative electrode active material layer is preferably 0.5 g / cm ³ or more and 2.0 g / cm ³ or less.

  Moreover, as nonaqueous electrolyte solution used for a battery, cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate ( DEC), chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, and γ-lactones such as γ-butyrolactone , 1,2-ethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, aceto Toamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl -2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. A lithium salt that dissolves in an organic solvent can be dissolved and used.

Examples of the lithium salt dissolved in these organic solvents include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , Examples thereof include LiN (CCF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, and the like. Moreover, it may replace with electrolyte solution and may use a polymer electrolyte and a solid electrolyte.

According to the present invention, the positive electrode active material consumed by the initial irreversible capacity inherent in the negative electrode active material composed of at least one selected from Si and Si oxide and C is converted to a higher capacity general formula Li _3-x. Lithium-containing composite nitride represented by M _x N (M is one or more transition metals selected from Co, Ni and Cu, 0 ≦ x ≦ 0.8) is used for charge and discharge after the first discharge By reducing the weight of the positive electrode active material that is not used, a non-aqueous electrolyte lithium ion secondary battery having a high energy density can be obtained.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a non-aqueous electrolyte lithium ion secondary battery of the present invention. As shown in FIG. 1, the non-aqueous electrolyte secondary battery of the present invention has a negative electrode 3 composed of a negative electrode active material layer 1 formed on a negative electrode current collector 2 such as a copper foil, and a positive electrode current collector 5 such as an aluminum foil. The positive electrode 6 formed of the positive electrode active material layer 4 is disposed so as to face the separator 7. As the separator 7, a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used. A negative electrode lead tab 9 and a positive electrode lead tab 10 for taking out electrode terminals are drawn out from the negative electrode 3 and the positive electrode 6, respectively, and are covered with an outer film 8 such as a laminate film except for the respective ends.

  The material structure of the negative electrode is composed of a negative electrode active material composed of at least one selected from Si and Si oxides and C capable of occluding and releasing lithium, and a binder resin, and a mixture of these negative electrode active materials Layer 1 is formed. These mixtures are processed into a known form by a manufacturing method such as applying a paste kneaded with a solvent onto a metal foil such as copper foil and rolling it, or directly pressing into a pressure-formed electrode plate. Specifically, Si powder, Si oxide powder, C powder, and binder resin, such as polyimide, polyamide, polyamideimide, polyacrylic acid resin, and polymethacrylic acid resin, can be used. It is formed by dispersing a kneading agent in a solvent such as N-methyl-2-pyrrolidone (NMP), kneading, applying onto the negative electrode current collector 2 made of metal foil, and drying in a high temperature atmosphere. .

As described above, carbon black, acetylene black, or the like may be mixed in the negative electrode active material layer 1 in order to impart conductivity as necessary. The electrode density of the generated negative electrode active material layer 1 is preferably 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. When the electrode density is low, the absolute value of the discharge capacity is small, and a merit over the conventional carbon material cannot be obtained. On the other hand, when it is high, it is difficult to impregnate the electrode with the electrolytic solution, and the discharge capacity is also lowered. The thickness of the negative electrode current collector 2 made of metal foil is preferably 4 to 100 μm because it is preferable to maintain the strength, and in order to increase the energy density, it is 5 to 30 μm. Is more preferable.

Material composition of the positive electrode, lithium nickelate, lithium manganate, lithium capable of absorbing and releasing oxides of the general formula _{Li 3-x M x N (} M lithium cobaltate or the like Co, Ni, 1 or more selected from Cu A positive electrode active material composed of a lithium-containing composite nitride represented by 0 ≦ x ≦ 0.8), a conductive agent such as carbon black or acetylene black for imparting conductivity, and a binder resin Thus, the positive electrode active material layer 4 is formed by a mixture of these.

Specifically, oxide powder capable of occluding and releasing lithium, lithium-containing composite nitride powder, conductive agent powder, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and vinylidene fluoride as binder resin. A positive electrode current collector made of metal foil by dispersing and kneading a binder resin typified by a ride-tetrafluoroethylene copolymer and polytetrafluoroethylene in a solvent such as N-methyl-2-pyrrolidone (NMP) or dehydrated toluene. It is formed by applying on the body 5 and drying in a high temperature atmosphere. The electrode density of the generated positive electrode active material layer 4 is preferably 2.0 g / cm ³ or more and 3.0 g / cm ³ or less. When the electrode density is low, the absolute value of the discharge capacity is small. On the other hand, when it is high, it is difficult to impregnate the electrode with the electrolytic solution, and the discharge capacity is also lowered. The thickness of the positive electrode current collector 5 made of metal foil is preferably 4 to 100 μm because it is preferable to maintain the strength, and is 5 to 30 μm in order to increase the energy density. Is more preferable.

  Moreover, as above-mentioned as electrolyte solution used for a battery, cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl Chain carbonates such as carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, and γ- such as γ-butyrolactone Lactones, chain ethers such as 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide , Acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3- An aprotic organic solvent such as methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. is used alone or in combination. The lithium salt that dissolves in these organic solvents is dissolved.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN ( CCF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides and the like. Moreover, it may replace with electrolyte solution and may use a polymer electrolyte and a solid electrolyte.

  Moreover, it is desirable that the non-aqueous electrolyte secondary battery manufactured as described above has a discharge end voltage value of 1.5 V or more and 2.7 V or less. There is a problem that the deterioration of the discharge capacity due to repeated charge / discharge increases as the discharge end voltage value decreases. Setting the voltage to 1.5 V or less has a high degree of difficulty in circuit design. Further, when the voltage is 2.7 V or more, the absolute value of the discharge capacity is small and no merit over the conventional carbon material can be obtained.

  In the battery of the present invention, the positive electrode active material consumed by the initial irreversible capacity inherent to the negative electrode active material comprising at least one selected from Si, Si oxide and C is made into a higher capacity lithium-containing composite nitride. By reducing the weight of the positive electrode active material that is not used for charge / discharge after the initial discharge, a non-aqueous electrolyte secondary battery having a high energy density can be obtained.

  Li is supplied from the positive electrode to the negative electrode active material in the negative electrode by the first charging operation. In the next initial discharge, the amount of Li returning from the negative electrode active material to the positive electrode is insufficient (irreversible capacity), so that Li is not supplied to the entire positive electrode, and an extra active material unrelated to charge / discharge is generated in the positive electrode. Therefore, an amount corresponding to the initial irreversible capacity or a portion corresponding to a part of the first irreversible capacity is previously included in the positive electrode, and the lithium-containing composite nitride having a larger capacity per unit weight than the oxide capable of inserting and extracting lithium. As a result, the weight of the extra active material is reduced as compared with the case of using only an oxide capable of inserting and extracting lithium. As a result, the energy density per unit weight of the battery increases.

  If the Li storage potential of the oxide capable of occluding and releasing lithium is lower than the Li storage potential of the lithium-containing composite nitride, there is no gain for replacing the lithium storage and release oxide with the lithium-containing composite nitride, and the energy density The battery is low, and no merit is obtained over the conventional battery.

  When the discharge voltage is 1.5 to 2.7 V and a lithium-containing composite nitride having an irreversible capacity or more is mixed in the positive electrode, lithium can be occluded and released in the positive electrode that accepts Li at the first discharge after the first charge. The oxide becomes insufficient, the capacity of the battery decreases, and the energy density decreases.

  The lithium-containing composite nitride in the positive electrode releases Li during the initial charge. When the initial charge capacity of the negative electrode active material is Y and the sum of the initial charge capacities of the oxide capable of occluding and releasing lithium and the lithium-containing composite nitride is Z, the negative electrode active material is such a relationship that Z ≦ Y. A specific high capacity effect can be obtained. On the other hand, if Z> Y, the capacity of the oxide capable of occluding and releasing lithium in the positive electrode cannot be fully utilized, and the energy density of the battery is lowered.

  Further, the lithium-containing composite nitride is composed of Li, one or more transition metals selected from Co, Ni, and Cu, and N, and there is no particular problem in terms of cost. In addition, since it does not react with other substances and is stable as compared with metallic lithium, it is excellent in work controllability and safety.

In the present invention, at least one selected from Si, SiO ₂ , and C is used as the negative electrode active material. In this example, the molar ratio is 1: 1: 0.8 as a representative example. Using.

Si powder, SiO ₂ powder, and C powder are commercially available as reagents, and these powders were obtained and used.

The charge / discharge performance of the oxide Si, SiO ₂ , C composite negative electrode to be used in advance was confirmed (capacity characteristics were confirmed between 2.0 V and 0.02 V using a model cell with metallic lithium as a counter electrode). In this charging, the Si, SiO ₂ , and C composite occluded about 2500 mAh / g of Li, but only discharged about 1650 mAh / g in the next discharge, and had an irreversible capacity of about 850 mAh / g. This value is α, and a capacity of about 34% of the charge capacity is an irreversible capacity, that is, α.

  In this example, lithium nickelate, lithium manganate, and lithium cobaltate were used as representative examples of oxides that can be stored and released in lithium in the positive electrode. These materials are commercially available as powder reagents, and these powders were obtained and used. Each charge / discharge performance was confirmed (capacity characteristics were confirmed between 4.3 V and 3.0 V by a model cell using metallic lithium as a counter electrode). As a result, lithium nickelate was about 200 mAh / g, and lithium manganate was about 120 mAh. / G, lithium cobaltate showed 150 mAh / g, and the charge / discharge potential was about 3.8 V, 4.0 V, and 3.7 V, respectively.

There is no commercially available lithium-containing composite nitride represented by the general formula Li _3-x M _x N (M is one or more transition metals selected from Co, Ni, Cu, 0 ≦ x ≦ 0.8), Separately synthesized as shown below.

  A commercial reagent lithium nitride powder and a commercial reagent transition metal powder were mixed in a predetermined amount and fired in a nitrogen atmosphere for 8 hours to obtain a sintered body of the target lithium-containing composite nitride. Further, this was pulverized to obtain a lithium-containing composite nitride powder. In addition, the process from mixing to grinding | pulverization was performed in the high purity nitrogen atmosphere of low humidity (dew point -30 degrees C or less). As a result of powder X-ray diffraction measurement of the obtained lithium-containing composite nitride, it was confirmed that the same hexagonal crystal pattern as that of lithium nitride appeared, there was no impurity peak, and the target lithium-containing composite nitride was formed.

Next, the charge / discharge performance at 1.4 V to 0.0 V of the lithium-containing composite nitride was confirmed (capacity characteristics confirmed by a model cell using metal lithium as a counter electrode). In this embodiment, as representative examples, transition metals are Co, Ni and Cu, and x = 0.4. The charge / discharge performance was about 800 mAh / g for Li _2.6 Co _0.4 N, about 500 mAh / g for Li _2.6 Ni _0.4 N, and about 600 mAh / g for Li _2.6 Cu _0.4 N. This value becomes each γ. The charge / discharge potential was around 1.3V. Therefore, since the lithium-containing composite nitride has a larger charge capacity than the oxide capable of occluding and releasing lithium, the use of the lithium-containing composite nitride for the positive electrode can provide a high-capacity battery. Since the charge / discharge potential of the object is low, the energy density of the battery decreases when it is involved in the initial discharge.

  In the lithium-containing composite nitride used in this example, the results were the same even when the transition metals were Co, Ni, and Cu and x = 0.5.

  In this example, the relationship between the lithium-containing composite nitride and the oxide capable of occluding and releasing lithium is such that when the charge / discharge capacity per unit weight of the lithium-containing composite nitride is B and the Li discharge potential is B ′, A <B and A ′> B ′ is satisfied.

The active material layer of the negative electrode was coated on a 10 μm copper foil with an electrode material mixed with Si, SiO ₂ , C composite material particles, polyimide as a binder, and NMP as a solvent, and dried at 125 ° C. for 5 minutes. A compression molding was performed by a roll press, and a drying treatment was performed again in a drying furnace at 350 ° C. for 30 minutes in an N ² atmosphere. The active material layer formed on this copper foil was punched out to 30 × 28 mm to form a negative electrode, and a negative electrode lead tab made of nickel for extracting electric charge was fused by ultrasonic waves.

For the active material layer of the positive electrode, an active material particle composed of the above-described oxide capable of absorbing and desorbing lithium and the above lithium-containing composite nitride, an electrode material in which polyvinylidene fluoride as a binder and NMP as a solvent are mixed are placed on a 20 μm aluminum foil. Then, it was prepared by drying at 125 ° C. for 5 minutes. The active material layer formed on the aluminum foil was punched out to 30 × 28 mm to form a positive electrode, and a positive electrode lead tab made of aluminum for taking out electric charges was fused by ultrasonic waves. After laminating in order of the negative electrode, the separator, and the positive electrode so that the active material layer faces the separator, the laminate film was sandwiched, the electrolyte solution was poured, and the laminate type battery was sealed under vacuum. Note that the electrolytic solution, the EC, and DEC, the volume ratio of EMC 3: 5: was used LiPF ₆ was dissolved in 1 mol / L to 2 mixture of.

When making this laminate type battery, the ratio of the charge capacity of the positive electrode to the charge capacity of the negative electrode is Y, the initial charge capacity of the Si, SiO ₂ , and C composite negative electrode is Y, the lithium occluding and releasing oxide and the lithium-containing composite nitride Y: Z = 1.00: 1.00 (Examples 1, 5, 9, 13, 17, 21) so that these relationships satisfy Z ≦ Y when the total initial charge capacity of the product is Z. 25, 29, 33), Y: Z = 1.10: 1.00 (Examples 2, 6, 10, 14, 18, 22, 26, 30, 34), Y: Z = 1.16: 1 .00 (Examples 3, 7, 11, 15, 19, 23, 27, 31, 35), Y: Z = 1.22: 1.00 (Examples 4, 8, 12, 16, 20, 24, 28, 32, 36). In addition, the amount of Li corresponding to the initial irreversible capacity of the Si, SiO ₂ , and C composite negative electrode is α, and the lithium-containing composite nitride Li _2.6 M _0.4 N (M is any of Co, Ni, or Cu) at the first charge. When the amount of Li released is γ, α = γ. For α = γ, the weight ratio of the negative electrode active material and the lithium-containing composite nitride was selected.

The charge / discharge test of the battery produced as described above was conducted at a constant current of 3 mA, the charge end voltage being 4.2 V, and the discharge end voltage being 2.5 V. Tables 1, 2 and 3 show the energy densities per total amount of the positive electrode active material and the negative electrode active material during the first and second charging of the battery in this test. Li _2.6 Co _0.4 N, Table 2 shows Li _2.6 Ni _0.4 N, and Table 3 shows Li _2.6 Cu _0.4 N. It can be seen that the difference between the energy density of the first time and the energy density of the second time is small, and the decrease in energy density due to the irreversible capacity of the Si, SiO _{2, and} C composites is minimized.

In the battery of the present invention, the amount of Li corresponding to the initial irreversible capacity of the Si, SiO ₂ , C composite negative electrode is α, and Li _2.6 M _0.4 N (M is one of Co, Ni, or Cu) at the time of initial charge. Even when α> γ when γ represents the amount of Li released from the substrate, the decrease in energy density can be suppressed. Table 4 shows the results of α = 2γ, and Table 5 shows the results of α = 3γ. Li _2.6 Co _0.4 N was typically used as the lithium-containing composite nitride at that time. The charge / discharge test of this battery was performed at a constant current of 3 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 2.5 V. In order to satisfy α> γ, the weight ratio between the negative electrode active material and the lithium-containing composite nitride was selected.

  In the battery of the present invention, the capacity per weight of the negative electrode active material at the time of the second charge is determined by the ratio of Y and Z, and as a representative so far, the negative electrode active material at the second charge of Examples 1 to 4 Table 6 shows the capacity per weight.

  Considering that the carbon material of the negative electrode of the lithium ion battery currently in practical use has a capacity density of about 300 to 370 mAh / g, the battery of the present invention has an extremely high capacity, and thus realizes a battery with a high energy density. It will be done.

Furthermore, in the lithium-containing composite nitride used in this example, when the transition metal is Co, Ni, Cu, and x = 0, the capacity per weight of the lithium-containing composite nitride increases to about 1500 mAh. / g. The effect is twice that of the case of Li _2.6 Co _0.4 N shown in this example.

(Comparative example)
For comparison with the present invention, in place of the battery of the present invention, a combination of Y: Z not satisfying Z ≦ Y, that is, Y: Z = 0.50: 1.00: where Z> Y (Comparative Example 1) 5, 9), Y: Z = 0.75: 1.00 (Comparative Examples 2, 6, 10), Y: Z = 0.80: 1.00 (Comparative Examples 3, 7, 11), Y: A battery was fabricated and a charge / discharge test was performed by selecting the weight ratio of the positive electrode and the negative electrode so that Z = 0.90: 1.00 (Comparative Examples 4, 8, and 12). This charge / discharge test was performed at a constant current of 3 mA, with a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V. At this time, α = γ, and Li _2.6 Co _0.4 N was typically used as the lithium-containing composite nitride. Table 7 shows the above results. It can be seen that the energy density at the first charge and the energy density at the second charge are very small.

Next, in place of the battery of the present invention, the weight ratio of the negative electrode active material and the lithium-containing composite nitride is selected so that 2α = γ and 5α = 2γ satisfying α <γ not satisfying α ≧ γ, A battery was prototyped and a charge / discharge test was conducted. This charge / discharge test was performed at a constant current of 3 mA, with a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V. At this time, Li _2.6 Co _0.4 N was typically used as the lithium-containing composite nitride under the condition of Z ≦ Y. Tables 8 and 9 show the results when 2α = γ and 5α = 2γ, respectively. The energy density during the second charge is very low.

For comparison, a battery was fabricated by combining Si, SiO ₂ , and C composite as a negative electrode active material and only an oxide capable of occluding and releasing lithium as a positive electrode active material (Comparative Examples 37 to 48), and a charge / discharge test. Went. Table 10 shows the energy density per total amount of the positive electrode active material and the negative electrode active material during the first and second charging of the battery in this test. The difference in energy density between the first charge and the second charge is large, and the energy density at the second charge is also small.

  Thus, the positive electrode active material consumed by the initial irreversible capacity inherent to the negative electrode active material composed of at least one selected from Si, Si oxide and C is changed to a higher capacity lithium-containing composite nitride, It was confirmed that a non-aqueous electrolyte secondary battery having a high energy density was obtained by reducing the weight of the positive electrode active material that was not used for charge and discharge after discharge.

Sectional drawing of the non-aqueous electrolyte lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode active material layer 2 Negative electrode current collector 3 Negative electrode 4 Positive electrode active material layer 5 Positive electrode current collector 6 Positive electrode 7 Separator 8 Exterior film 9 Negative electrode lead tab 10 Positive electrode lead tab

Claims (5)

General formula for the positive electrode active material: Li _3-x M _x N
(M is one or more transition metals selected from Co, Ni and Cu, 0 ≦ x ≦ 0.8)
A non-aqueous electrolyte lithium ion secondary battery comprising a lithium-containing composite nitride represented by:   The lithium-containing composite nitride and an oxide capable of occluding and releasing lithium are used as a mixed active material for the positive electrode active material, and at least one or more selected from Si, Si oxide and C capable of occluding and releasing lithium in the negative electrode active material The non-aqueous electrolyte lithium ion secondary battery according to claim 1, comprising a mixed active material comprising:   The charge / discharge capacity per unit weight of the oxide capable of occluding and releasing lithium contained in the positive electrode active material is A, the Li emission potential is A ′, and the charge / discharge per unit weight of the lithium-containing composite nitride is The non-aqueous electrolyte lithium ion secondary battery according to claim 2, wherein A <B and A '> B' are satisfied when the capacity is B and the Li emission potential is B '.   When the amount of Li corresponding to the initial irreversible capacity of the negative electrode active material is α and the amount of Li released by the lithium-containing composite nitride at the time of initial charge is γ, the weight of the negative electrode active material and the lithium-containing composite nitride 4. The non-aqueous electrolyte lithium ion secondary battery according to claim 2, wherein the ratio is selected so as to satisfy α ≧ γ. 5.   When the initial charge capacity of the negative electrode active material is Y and the total of the initial charge capacity of the oxide capable of occluding and releasing lithium and the lithium-containing composite nitride is Z, these relations satisfy Z ≦ Y. The nonaqueous electrolyte lithium ion secondary battery according to any one of claims 2 to 4.

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