JP5021982B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a nonaqueous electrolyte secondary battery in which a positive electrode includes a positive electrode active material including a lithium-containing manganese oxide, and a negative electrode includes a negative electrode active material including silicon and a transition metal element.

  Nonaqueous electrolyte secondary batteries (particularly lithium secondary batteries) have high electromotive force and high energy density, and are therefore widely used as main power sources for mobile communication devices and portable electronic devices. The demand for non-aqueous electrolyte secondary battery as a memory backup power source is increasing year by year. With the remarkable development of portable electronic devices, further downsizing, higher performance and maintenance-free operation of the devices are being promoted. Accordingly, there is a strong demand for non-aqueous electrolyte secondary batteries with higher energy density than conventional ones.

  From the viewpoint of increasing the capacity of lithium secondary batteries, silicon-based materials, which are negative electrode materials having a larger theoretical capacity than carbon materials, are attracting attention. The theoretical capacity of silicon is larger than that of graphite and aluminum.

  However, crystalline silicon causes a volume change when inserting or extracting lithium ions during charge and discharge. The expansion rate of the volume is about 4 times at the maximum. When silicon is used as an active material, the electrode structure is destroyed because silicon is pulverized due to strain due to volume change.

  Patent Document 1 proposes to use silicon oxide as the negative electrode active material. When silicon oxide occludes lithium ions, it changes to a microcrystalline structure of an alloy of lithium and silicon and lithium oxide. Thereby, the intensity | strength with respect to the distortion by a volume change increases, and pulverization is suppressed. On the other hand, when lithium ions are released until the negative electrode active material is completely discharged, the alloy of lithium and silicon is changed to silicon and lithium oxide is not changed. However, complete discharge of the negative electrode active material is not possible in actual battery use. Therefore, in the discharge state, an alloy of lithium and silicon having a reduced lithium ratio and lithium oxide exist.

  Clock backup power supplies such as digital still cameras are often left in the equipment, but often do not have a discharge cut protection circuit. As a result, the backup power supply is often discharged (deep discharge) until the battery voltage reaches around 0V. Life characteristics in a charge / discharge cycle including deep discharge (deep discharge cycle) are particularly important in a backup power supply.

When manganese oxide is used for the positive electrode active material and graphite is used for the negative electrode active material, since the polarization is small when the battery voltage is discharged at a low rate (eg, about 0.1 C, 1 C is 1 hour rate current) to near 0 V, the positive electrode And the electric potential of a negative electrode becomes substantially equal. In such a case, the potential range excellent in reversibility of the positive electrode (1.8 V or more with respect to metallic lithium (Li / Li ⁺ )) and the potential range excellent in reversibility of the negative electrode (relative to metallic lithium (Li / Li ⁺ )). Therefore, it is impossible to achieve both of 0.2V or less. When deep discharge is performed, at least one of the positive electrode active material and the negative electrode active material deteriorates, and the deterioration of the life characteristics increases.

  Patent Document 2 proposes mixing a lithium-containing compound that releases lithium ions at a potential of 2 V or less with a carbon material that is a negative electrode active material, from the viewpoint of preventing elution of the negative electrode current collector during deep discharge. ing. The proposal of Patent Document 2 is effective for a battery including a copper negative electrode current collector. However, a battery for use as a clock backup power source or the like does not have a negative electrode current collector because a negative electrode mixture molded body (pellet) is generally used as a negative electrode.

  Patent Document 3 proposes to reduce the variation in end-of-discharge voltage by reducing the voltage change rate of each battery from the viewpoint of preventing deep discharge of a specific battery in a series-connected assembled battery. The proposal of Patent Document 3 is premised on the use of a plurality of batteries connected in series and the presence of a discharge voltage control system.

  As proposed in Patent Document 1, when silicon oxide is used as the negative electrode active material, the deep discharge cycle life is shortened. It has been found that when the deep discharge cycle is repeated, the amount of film formed on the active material surface increases rapidly.

  The rapid increase in the coating amount is thought to be due to the tendency of non-uniformity in the distribution of electronic resistance in the negative electrode active material due to deep discharge and the non-uniformity of the reaction to proceed. In the portion where the reaction is concentrated, a lot of film is formed and the deterioration of the portion proceeds. As a result, the reaction concentrates in another part, and the generation and deterioration of the film progress at an accelerated rate.

  The reason why the electron resistance distribution in the negative electrode active material is non-uniform is that the silicon oxide in the deep discharge state has a significant increase in electronic resistance. In the deeply discharged silicon oxide, the lithium ratio in the alloy of lithium and silicon produced during charging is small, so the resistance of the alloy is large.

When a manganese oxide is used as a positive electrode active material and a silicon oxide is used as a negative electrode active material, in a battery design having a large negative electrode capacity with respect to the positive electrode, the potential of the positive electrode with respect to metallic lithium (Li / Li ⁺ ) is 1.8 V during deep discharge. Get smaller. As a result, the crystal structure of the manganese oxide may change irreversibly.
JP 2000-243449 A JP 7-335201 A JP 2001-243943 A

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery having high capacity and excellent life characteristics in a deep discharge cycle (deep discharge cycle life) in which deterioration of a positive electrode active material and a negative electrode active material is suppressed. To do.

The present invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte from the viewpoint of providing a battery having a high capacity and excellent life characteristics in a deep discharge cycle (deep discharge cycle life). The positive electrode comprises a lithium-containing manganese oxide. The negative electrode includes a negative electrode active material that is an alloy of silicon and a transition metal element, and the potentials of the positive electrode and the negative electrode at a battery voltage of 0 V are respectively relative to metal lithium (Li / Li ⁺ ). The present invention relates to a non-aqueous electrolyte secondary battery that is 1.8 V or higher.

Here, the lithium-containing manganese oxide includes, for example, at least one selected from the group consisting of Li _0.55 MnO ₂ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ and Li ₂ Mn ₄ O ₉ .

Transition metal element contained in the anode active material is at least one selected from the group consisting of titanium, nickel and iron.

  In the negative electrode active material, the molar ratio of silicon to the transition metal element is preferably 67:33 to 98: 2, and more preferably 74:26 to 95: 5.

  A part of manganese in the lithium-containing manganese oxide can be replaced with another element Me. The element Me is preferably at least one selected from the group consisting of nickel and iron. The molar ratio of the element Me to manganese in the lithium-containing manganese oxide is preferably 1/3 or less.

  The negative electrode includes, for example, a molded body of a negative electrode mixture. The negative electrode mixture includes a negative electrode active material. The thickness of the molded body is preferably 0.05 mm to 2.0 mm. In this case, the negative electrode may not have a current collector.

  The positive electrode includes, for example, a molded body of a positive electrode mixture. The positive electrode mixture includes a positive electrode active material. The thickness of the molded body is preferably 0.30 mm to 3.0 mm. In this case, the positive electrode may not have a current collector.

  The present invention further relates to a backup power source having the non-aqueous electrolyte secondary battery, such as a clock backup power source and a memory backup power source.

  ADVANTAGE OF THE INVENTION According to this invention, degradation of a positive electrode active material and a negative electrode active material can be suppressed, and the nonaqueous electrolyte secondary battery excellent in the deep capacity | capacitance and deep discharge cycle life can be provided.

As a result of intensive studies, the inventors have conducted a charge / discharge cycle in which discharge is performed until the negative electrode potential is approximately 2.0 V with respect to metallic lithium when an alloy containing silicon and a transition metal element is used as the negative electrode active material. It has been found that the coating film formed on the surface of the negative electrode active material does not rapidly increase even if it is repeated. It is presumed that this is related to the fact that the electronic resistance of the intermetallic compound phase of silicon and transition metal is low, and the increase in the electronic resistance of the negative electrode active material at the end of discharge can be suppressed. For example, an alloy of silicon and titanium includes a silicon phase and a titanium disilicide phase having a low electronic resistance. The powder electronic resistance of an alloy of silicon and titanium is 10 ⁻⁴ to 10 ⁻⁷ times that of silicon alone.

The present invention is based on the above findings, and includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material including a lithium-containing manganese oxide. The negative electrode includes silicon and a transition metal element. The present invention relates to a non-aqueous electrolyte secondary battery that includes a negative electrode active material and has a positive electrode potential and a negative electrode potential of 1.8 V or more with respect to metallic lithium (Li / Li ⁺ ) when the battery voltage is 0 V.

By designing the battery so that the potential of the positive electrode and negative electrode when the battery voltage is 0 V is 1.8 V or more with respect to metallic lithium (Li / Li ⁺ ), the deterioration of the positive electrode active material and the negative electrode active material is suppressed. Thus, a non-aqueous electrolyte secondary battery having a high capacity and an excellent deep discharge cycle life can be obtained.

It is obvious to those skilled in the art how to design a battery so that the potential of the positive electrode and the negative electrode when the battery voltage is 0 V is 1.8 V or more with respect to metallic lithium (Li / Li ⁺ ).

Li _0.55 MnO ₂ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₄ O _9, etc. may be used as the lithium-containing manganese oxide constituting the positive electrode active material from the viewpoint of capacity density and stability. preferable. These may be used alone or in combination of two or more. These compositions are compositions before charging and discharging the battery, and the lithium content and the like change due to charging and discharging.

  The lithium-containing manganese oxide can be obtained, for example, by mixing a lithium source and a manganese source, and firing the obtained mixture in an oxygen-containing atmosphere (for example, in air or oxygen). Examples of the lithium source include lithium hydroxide, lithium carbonate, and lithium acetate. Examples of the manganese source include manganese dioxide, manganese carbonate, manganese acetate and the like.

The positive electrode potential is preferably 1.8 V or more, more preferably 2.0 V or more, with respect to metallic lithium even during deep discharge, that is, when the battery voltage is 0 V. When the positive electrode potential is smaller than 1.8 V, the reversibility of the reaction decreases due to damage to the crystal structure of the lithium-containing manganese oxide.

  A part of manganese of the lithium-containing manganese oxide may be substituted with another element Me. As the element Me, for example, nickel, iron and the like are preferable. In the lithium-containing manganese oxide, one kind of element Me may be contained alone or a plurality of kinds of elements Me may be contained. When the lithium-containing manganese oxide contains the element Me, the change in the valence of manganese during charging and discharging is reduced. As a result, elution of manganese is suppressed and the deep discharge cycle life is improved.

  The molar ratio of the element Me to manganese in the lithium-containing manganese oxide is preferably 1/3 or less, and more preferably 1/4 or less. That is, the amount of manganese substituted with the element Me is preferably 33.3% or less, more preferably 25% or less. Although the detailed cause is not clarified, when the amount of manganese substituted with the element Me exceeds 1/3 of the whole, the capacity of the positive electrode active material decreases.

  Lithium-containing manganese oxide in which Mn is replaced with element Me is prepared by, for example, mixing a lithium source, a manganese source, and an element Me source, and firing the obtained mixture in an oxygen-containing atmosphere (for example, in air or oxygen). Can be obtained. Examples of the element Me source include nickel hydroxide.

The specific surface area of the positive electrode active material is not particularly limited, but is preferably ^{2 to} 100 m ² / g. When the specific surface area is less than 2 m ² / g, the reaction area is small and a sufficient capacity may not be obtained. When the specific surface area exceeds 100 m ² / g, the necessary amount of conductive agent increases or the electronic resistance increases, and the battery capacity may also decrease.

The average particle diameter of the positive electrode active material (median diameter in the volume-based particle size distribution: D ₅₀ ) is not particularly limited, but is preferably 0.1 to 100 μm. If the average particle size is less than 0.1 μm, the reaction area is small and sufficient capacity may not be obtained. If the average particle size exceeds 100 μm, the amount of necessary conductive agent increases or the electronic resistance increases, and the battery capacity may also decrease.

The negative electrode active material contains silicon and a transition metal element. As the transition metal element, chromium, manganese, iron, cobalt, nickel, copper, molybdenum, silver, titanium, zirconium, hafnium, tungsten, or the like can be used. The negative electrode active material may contain one type of transition metal element alone, or may contain multiple types of transition metal elements. In particular, a negative electrode active material containing at least one selected from the group consisting of titanium, nickel, and iron (for example, titanium disilicide: TiSi ₂ ) has a low electronic resistance, is easily available, and is preferable from an industrial viewpoint.

  In the negative electrode active material containing silicon and a transition metal element, the molar ratio of silicon to the transition metal element is preferably 67:33 to 98: 2. When the proportion of silicon is smaller than 67 mol% (the proportion of transition metal element is larger than 33 mol%), the proportion of the active phase (for example, a silicon simple substance phase) with respect to lithium in the negative electrode active material is reduced. The capacity density of the negative electrode active material decreases. When the proportion of silicon is greater than 98 mol% (the proportion of transition metal element is less than 2 mol%), the volume expansion coefficient of the negative electrode active material when lithium is occluded is substantially equivalent to that of silicon alone. Therefore, it becomes difficult to maintain the current collecting structure in the negative electrode, and the capacity maintenance rate in the charge / discharge cycle is lowered.

  When the transition metal element is Ti, the content of silicon contained in the negative electrode active material is desirably 72.4 to 97.7 mol%. When the transition metal element is Ni, the content of Si contained in the negative electrode active material is desirably 69.4 to 97.45 mol%. When the transition metal element is Fe, the content of Si contained in the negative electrode active material is desirably 70 to 97.5 mol%.

In particular, the molar ratio between silicon and the transition metal element of 74:26 to 95: 5 is most effective in achieving both a high capacity and an excellent capacity maintenance ratio.
The negative electrode potential is not particularly limited when the negative electrode does not contain graphite as an active material or a conductive agent. However, when the negative electrode contains graphite, the negative electrode potential is preferably 0.25 V or less with respect to metallic lithium at normal discharge, that is, when the battery voltage is 2.0 V or more, and 0.2 V or less. More preferably it is. This is because graphite deteriorates when the charge / discharge cycle is repeated in a range where the negative electrode potential exceeds 0.25 V with respect to metallic lithium.

  When the battery voltage is 0 V, the positive and negative electrodes have the same potential. Therefore, at the time of deep discharge, that is, when the battery voltage is 0 V, the negative electrode potential is preferably 1.8 V or more, more preferably 2.0 V or more with respect to metallic lithium.

  From the viewpoint of achieving both high capacity and low electronic resistance, the negative electrode active material is an alloy of silicon and a transition metal element, and has at least two phases of a single silicon phase and an intermetallic compound phase of silicon and the transition metal element. It is preferable to include the above.

  The silicon single phase may contain a small amount of additive elements such as phosphorus (P), boron (B), hydrogen (H), transition metal elements and the like. The intermetallic compound phase has a high affinity with the single silicon phase, and even if the volume of the alloy expands during charging, peeling is unlikely to occur at the interface with the single silicon phase. The intermetallic compound phase has higher electron conductivity and higher hardness than the silicon simple substance phase. Multiple types of intermetallic compound phases may be present in the alloy.

  The crystallinity of the negative electrode active material is not particularly limited, but is desirably in an amorphous state, a microcrystalline state, or a mixed state of an amorphous region and a microcrystalline region. The amorphous state is a state in which a diffraction image (diffraction pattern) does not have a clear peak attributed to a crystal plane and only a broad diffraction image is obtained in X-ray diffraction analysis using CuKα rays. . The microcrystalline state is a state in which the crystal grain size is 20 nm or less. These states can be directly observed with a transmission electron microscope (TEM). The crystallite size can be determined from the half width of the peak in the diffraction image obtained by X-ray diffraction analysis, using the Scherrer equation. When there are a plurality of peaks, the half width of the peak with the highest intensity is obtained, and the Scherrer equation is applied thereto. When the crystallite size is larger than 20 nm, the mechanical strength of the active material particles may not be able to follow the volume change of the active material accompanying charge / discharge. Therefore, particle cracking or the like may occur, the current collection state may deteriorate, and charge / discharge efficiency or life characteristics may deteriorate.

  A method for obtaining the negative electrode active material in an amorphous state, a microcrystalline state, or a mixed state of an amorphous region and a microcrystalline region is not particularly limited. For example, a method of directly synthesizing a single element of silicon and a single element of the transition metal element M by mechanically pulverizing or mixing with a ball mill, a vibration mill, a planetary ball mill, or the like (mechanical alloying method) can be used. From the viewpoint of efficiently performing mechanical alloying, it is most preferable to use a vibration mill.

Although the specific surface area of a negative electrode active material is not specifically limited, It is preferable that it is 0.5-20 m < ² > / g. If the specific surface area is less than 0.5 m ² / g, the contact area between the negative electrode active material and the non-aqueous electrolyte is small, and the charge / discharge efficiency may be reduced. When the specific surface area exceeds 20 m ² / g, the reactivity between the negative electrode active material and the non-aqueous electrolyte becomes excessive, and the irreversible capacity may increase.

The average particle diameter of the negative electrode active material (median diameter in the volume-based particle size distribution: D ₅₀ ) is not particularly limited, but is preferably 0.1 to 20 μm. When the average particle size is less than 0.1 μm, the specific surface area of the negative electrode active material is large, so that the reactivity between the negative electrode active material and the nonaqueous electrolyte becomes excessive, and the irreversible capacity may increase. When the average particle size exceeds 20 μm, the specific surface area of the negative electrode active material is small, so that the contact area between the negative electrode active material and the non-aqueous electrolyte decreases, and the charge / discharge efficiency may decrease.

  A film containing silicon oxide is preferably formed on the surface of the negative electrode active material from the viewpoint of safety. As a method for forming such a film, for example, a method of gradually introducing oxygen into the negative electrode active material being stirred in a sealed container having a stirring function can be mentioned. By cooling the hermetic container with a heat radiation mechanism such as a water cooling jacket, the temperature rise of the stirred negative electrode active material can be suppressed, and the time required for film formation is shortened. Specifically, a vibration dryer or a kneader equipped with a heat dissipation mechanism can be used.

  The positive electrode is preferably a molded body of a positive electrode mixture (for example, coin-shaped pellets). The positive electrode mixture includes a positive electrode active material as an essential component, and includes a binder, a conductive agent, and the like as optional components. When the positive electrode is a molded body, a current collector is not necessary, and the capacity of the positive electrode can be increased. In particular, in a battery having a small size, such as a battery for use as a backup power source, it is advantageous to use a molded body.

  The size of the molded body of the positive electrode mixture is preferably 0.30 mm to 3.0 mm in thickness in both the charged state and the discharged state. When the thickness of the molded body is smaller than 0.30 mm, the energy density of the positive electrode is smaller than that of the negative electrode in a battery design in which the potential of the positive electrode and the negative electrode is 1.8 V or more with respect to metallic lithium when the battery voltage is 0 V Become. Therefore, the thickness of the negative electrode facing the positive electrode is smaller than the lower limit of 0.05 mm. When the thickness of the molded body exceeds 3.0 mm, the diffusibility of lithium ions in the positive electrode is extremely lowered, and the charge / discharge efficiency may be lowered.

  The negative electrode is preferably a molded body of a negative electrode mixture (for example, coin-shaped pellets). The negative electrode mixture includes a negative electrode active material as an essential component, and includes a binder, a conductive agent, and the like as optional components. When the negative electrode is a molded body, a current collector is not necessary, and the capacity of the negative electrode can be increased. In particular, in a battery having a small size, such as a battery for use as a backup power source, it is advantageous to use a molded body.

  The size of the molded body of the negative electrode mixture is preferably 0.05 mm to 2.0 mm in thickness in both the charged state and the discharged state. If the thickness of the molded body is smaller than 0.05 mm, the strength of the molded body is lowered, shape retention becomes difficult, and battery characteristics may be degraded. When the thickness of the molded body exceeds 2.0 mm, the diffusibility of lithium ions in the negative electrode is extremely lowered, and the charge / discharge efficiency may be lowered.

  The thickness of the molded body of the positive electrode mixture and the molded body of the negative electrode mixture can be confirmed by sectional X-ray CT or the like without disassembling the battery.

  Examples of the conductive agent included in the positive electrode mixture or the negative electrode mixture include graphite such as natural graphite (flaky graphite, etc.), artificial graphite, expanded graphite, acetylene black, ketjen black, channel black, furnace black, and lamp black. And carbon blacks such as thermal black, carbon fibers, metal fibers and the like. These may be used alone or in combination. Of these, graphites and carbon blacks are preferably used from the viewpoints of density, stability, price, and the like.

  The conductive agent contained in the positive electrode mixture is particularly preferably acetylene black or ketjen black, and the amount is preferably 1 to 20 parts by weight per 100 parts by weight of the positive electrode active material.

  The conductive agent contained in the negative electrode mixture is particularly preferably carbon black or a combination of graphite and carbon black, and the amount is preferably 2 to 40 parts by weight per 100 parts by weight of the negative electrode active material.

  Examples of the binder included in the positive electrode mixture or the negative electrode mixture include styrene butadiene rubber, polyacrylic acid, polyethylene, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), carboxymethyl cellulose, Examples include methyl cellulose. These may be used alone or in combination. Among these, styrene butadiene rubber that can respond to the volume change of the active material relatively flexibly, polyacrylic acid that can maintain strong binding, and the like are preferable.

  The binder contained in the positive electrode mixture is particularly preferably polytetrafluoroethylene, and the amount thereof is preferably 1 to 20 parts by weight per 100 parts by weight of the positive electrode active material.

  The binder to be included in the negative electrode mixture is particularly preferably polyacrylic acid, and the amount is preferably 2 to 30 parts by weight per 100 parts by weight of the negative electrode active material.

The non-aqueous electrolyte is preferably a non-aqueous solvent in which a lithium salt is dissolved.
Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, and γ-lactones such as γ-butyrolactone 1, 2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethylsulfoxy 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, 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, butyl diglyme, methyl tetraglyme, etc. Examples include aprotic organic solvents. These are preferably used in combination.

Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , Examples include lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, and imides. These may be used alone or in combination. The concentration of the lithium salt dissolved in the non-aqueous solvent is preferably 0.2 to 2.0 mol / L, and more preferably 0.5 to 1.5 mol / L.

  As the separator interposed between the positive electrode and the negative electrode, a microporous thin film having high ion permeability, predetermined mechanical strength, and electronic insulation is used. In particular, a microporous thin film made of a material such as polypropylene, polyethylene, polyphenylene sulfide, polyethylene terephthalate, polyamide, or polyimide is preferably used.

  The shape of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and may be a cylindrical shape, a square shape, a coin shape, or the like. However, the present invention is particularly suitable for a coin-type non-aqueous electrolyte secondary battery. A coin-type non-aqueous electrolyte secondary battery has a coin-type battery case including a positive electrode can and a negative electrode can, and the positive electrode and the negative electrode are each in a disc shape and are accommodated in the positive electrode can and the negative electrode can. A separator is interposed between the positive electrode and the negative electrode. The open end of the positive electrode can and the open end of the negative electrode can are fitted via an insulating gasket, and the battery is sealed. The battery is sealed after the positive electrode, the negative electrode, and the separator are impregnated with a lithium ion conductive nonaqueous electrolyte.

  Next, the present invention will be specifically described based on examples. However, the present invention is not limited to the following examples.

(I) Production of positive electrode Manganese dioxide and lithium hydroxide were mixed at a molar ratio of 20:11. The obtained mixture was calcined in the air at 400 ° C. for 12 hours to obtain Li _0.55 MnO ₂ having an average particle diameter of 10 μm and a BET specific surface area of 20 m ² / g. Li _0.55 MnO ₂ that is a positive electrode active material, acetylene black that is a conductive agent, and polytetrafluoroethylene (PTFE) that is a binder are mixed in a weight ratio of 88: 6: 6, and a positive electrode mixture is obtained. Obtained. PTFE as a binder was used in the state of an aqueous dispersion. The positive electrode mixture was formed into coin-shaped pellets having a diameter of 4 mm and a thickness of 1.0 mm. A product obtained by drying the obtained molded body at 250 ° C. for 12 hours was used as a positive electrode.

(Ii) Production of negative electrode A silicon-titanium alloy was synthesized in the following manner.
Silicon powder and titanium powder were mixed so that the molar ratio (atomic ratio) of silicon element to titanium element was 85:15. 1.7 kg of the obtained mixture was put together with 300 kg of stainless steel balls having a diameter of 1 inch into a vibration ball mill apparatus FV-20 type (made of stainless steel, internal volume 64 L) manufactured by Chuo Kakoki Co., Ltd. After the air in the apparatus was replaced with argon gas, the mixture was pulverized for 60 hours at an amplitude of 8 mm and a vibration frequency of 1200 rpm to obtain a silicon-titanium alloy.

  When the silicon-titanium alloy was analyzed by X-ray diffraction (XRD), it was found that the silicon-titanium alloy contained at least a single silicon phase and a titanium disilicide phase. When the crystallite size was calculated using the peak position of the diffraction image, the half width, and Scherrer's equation, the silicon simple substance phase was amorphous and the titanium disilicide phase was 15 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 50:50, assuming that all titanium formed titanium disilicide.

  This silicon-titanium alloy was recovered in a vibration dryer VU30 type manufactured by Chuo Kakoki Co., Ltd. while maintaining an argon atmosphere. A mixed gas of argon and oxygen was intermittently introduced over 1 hour into the silicon-titanium alloy that was vibrated and stirred in the vibration dryer so that the temperature of the alloy did not exceed 100 ° C. As a result, a film containing silicon oxide was formed on the surface of the alloy particles. Thereafter, alloy particles classified so as to have a maximum particle size of 63 μm were used as the negative electrode active material.

  A silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 120: 10: 10 to obtain a negative electrode mixture. The negative electrode mixture was formed into pellets having a diameter of 4 mm and a thickness of 0.3 mm. The obtained molded body was dried at 200 ° C. for 12 hours to make a negative electrode.

(Iii) Preparation of nonaqueous electrolyte Propylene carbonate (PC): ethylene carbonate (EC): 1,2-dimethoxyethane (DME) = 1: 1: 1 mixed with a nonaqueous solvent, and the resulting mixture A solution obtained by dissolving LiN (CF ₃ SO ₂ ) ₂ as a lithium salt in a solvent at a concentration of 1 mol / liter was used as a non-aqueous electrolyte.

(Iv) Production of Test Battery A coin type battery having a diameter of 6.8 mm and a thickness of 2.1 mm as shown in FIG. 1 was produced. The positive electrode can 1 also serves as a positive electrode terminal and is made of stainless steel having excellent corrosion resistance. The negative electrode can 2 also serves as a negative electrode terminal and is made of stainless steel made of the same material as the positive electrode can 1. The gasket 3 is made of polypropylene and insulates the positive electrode can 1 and the negative electrode can 2. A pitch is applied between the positive electrode can 1 and the gasket 3 and between the negative electrode can 2 and the gasket 3.

  The silicon-titanium alloy that is the negative electrode active material needs to be alloyed with lithium. Therefore, a lithium foil was pressure-bonded to the surface (separator side) of the negative electrode 5 during battery assembly. After the battery was assembled, the lithium foil was electrochemically occluded in the negative electrode in the presence of a non-aqueous electrolyte, and a lithium alloy was produced inside the negative electrode 5. A separator 6 made of a polypropylene nonwoven fabric was disposed between the positive electrode 4 and the negative electrode 5.

  The positive electrode was 41.3 mg and the negative electrode was 4.6 mg so that the potential of the positive electrode and the negative electrode with respect to metallic lithium during deep discharge (when the battery voltage was discharged to 0 V) was 2.0 V. The battery was filled with 15 μL of nonaqueous electrolyte. The amount of the lithium foil to be bonded to the negative electrode 5 was set to 4.0 μL so that the initial discharge capacity at the time of deep discharge was 7.0 mAh in consideration of the irreversible capacity. The obtained battery is referred to as A1.

  The positive electrode was 39.1 mg so that the potential of the positive electrode and the negative electrode against metallic lithium during deep discharge (when the battery voltage was discharged to 0 V) was 1.8 V, and the initial discharge capacity during deep discharge was 7.0 mAh. A battery A2 was produced in the same manner as in Example 1 except that the amount of lithium foil was changed.

<< Comparative Example 1 >>
The positive electrode is 35.5 mg so that the potential of the positive electrode and the negative electrode with respect to metallic lithium during deep discharge (when the battery voltage is discharged to 0 V) is 1.5 V, and the initial discharge capacity during deep discharge is 7.0 mAh. A battery A3 was produced in the same manner as in Example 1 except that the amount of lithium foil was changed.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 67:33. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The silicon simple substance phase was amorphous, and the crystallite size of the titanium disilicide phase was 15 nm. The weight ratio of the titanium disilicide phase to the silicon single phase was 99: 1, assuming that all titanium formed titanium disilicide.

  The same method as in Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 114: 20: 10. Thus, a negative electrode was produced. Using this negative electrode, the battery was prepared in the same manner as in Example 2 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when the battery voltage was discharged to 0 V) was 4.5 mAh. A4 was produced.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 74:26. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The silicon simple substance phase was amorphous, and the crystallite size of the titanium disilicide phase was 15 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 82:18 assuming that all titanium formed titanium disilicide.

  A method similar to Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 100: 20: 10. Thus, a negative electrode was produced. A battery A5 was produced in the same manner as in Example 2 except for the use of this negative electrode.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 78:22. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The silicon simple substance phase was amorphous, and the crystallite size of the titanium disilicide phase was 15 nm. The weight ratio between the titanium disilicide phase and the silicon simple substance phase was 70:30, assuming that all titanium formed titanium disilicide.

  A method similar to Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 94:20:10. Thus, a negative electrode was produced. A battery A6 was produced in the same manner as in Example 2 except for the use of this negative electrode.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 90:10. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The silicon simple substance phase was amorphous, and the crystallite size of the titanium disilicide phase was 15 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 35:65 assuming that all titanium formed titanium disilicide.

  A method similar to Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 77:20:10. Thus, a negative electrode was produced. A battery A7 was produced in the same manner as in Example 2 except for the use of this negative electrode.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 95: 5. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The crystallite size of the silicon simple substance phase was 9 nm, and the crystallite size of the titanium disilicide phase was 11 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 18:82 assuming that all titanium formed titanium disilicide.

  A method similar to Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed in a weight ratio of 71:20:10. Thus, a negative electrode was produced. A battery A8 was produced in the same manner as in Example 2 except for the use of this negative electrode.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 98: 2. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The crystallite size of the silicon simple substance phase was 9 nm, and the crystallite size of the titanium disilicide phase was 11 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 7:93, assuming that all titanium formed titanium disilicide.

  A method similar to Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 67:20:10. Thus, a negative electrode was produced. A battery A9 was produced in the same manner as in Example 2 except for the use of this negative electrode.

  A silicon-titanium alloy was synthesized in the same manner as in Example 1 except that silicon powder and titanium powder were mixed so that the molar ratio of silicon element to titanium element was 99: 1. As a result of XRD analysis, it was found that the obtained silicon-titanium alloy contained at least a silicon simple substance phase and a titanium disilicide phase. The crystallite size of the silicon simple substance phase was 9 nm, and the crystallite size of the titanium disilicide phase was 11 nm. The weight ratio of the titanium disilicide phase to the silicon simple substance phase was 4:96, assuming that all titanium formed titanium disilicide.

  The same method as in Example 1 except that a silicon-titanium alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed in a weight ratio of 66:20:10. Thus, a negative electrode was produced. A battery A10 was produced in the same manner as in Example 2 except for the use of this negative electrode.

Nickel powder was used instead of titanium powder.
A silicon-nickel alloy was synthesized in the same manner as in Example 1 except that silicon powder and nickel powder were mixed so that the molar ratio of silicon element to nickel element was 84.4: 15.6. . As a result of XRD analysis, it was found that the obtained silicon-nickel alloy contained at least a single silicon phase and a nickel disilicide phase. However, since the peak positions overlap, it was impossible to separate the silicon simple substance phase from the nickel disilicide phase. The crystallite size of the alloy was 12 nm. The weight ratio of the nickel disilicide phase to the silicon simplex phase was 54:46 assuming that all nickel formed nickel disilicide.

  The same method as in Example 1 except that a silicon-nickel alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 91:20:10. Thus, a negative electrode was produced. A battery B1 was produced in the same manner as in Example 2 except that this negative electrode was used.

Iron powder was used instead of titanium powder.
A silicon-iron alloy was synthesized in the same manner as in Example 1 except that silicon powder and iron powder were mixed so that the molar ratio of silicon element to iron element was 84:16. As a result of XRD analysis, it was found that the obtained silicon-iron alloy contained at least a single silicon phase and an iron disilicide phase. The silicon simple substance phase was amorphous, and the crystallite size of the iron disilicide phase was 15 nm. The weight ratio between the iron disilicide phase and the silicon simple substance phase was 55:45 assuming that all iron formed iron disilicide.

  The same method as in Example 1 except that a silicon-iron alloy as a negative electrode active material, carbon black as a conductive agent, and polyacrylic acid as a binder were mixed at a weight ratio of 93:20:10. Thus, a negative electrode was produced. A battery C1 was produced in the same manner as in Example 2 except that this negative electrode was used.

<< Comparative Example 2 >>
Graphite powder was used as the negative electrode active material. A negative electrode was produced in the same manner as in Example 1, except that graphite, carboxymethyl cellulose and styrene butadiene rubber as binders were mixed at a weight ratio of 100: 1: 1. Using this negative electrode, in the same manner as in Example 1 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D1 was produced.

<< Comparative Example 3 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 2 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when the battery voltage was discharged to 0 V) was 4.5 mAh, Battery D2 was produced.

<< Comparative Example 4 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Comparative Example 1 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D3 was produced.

<< Comparative Example 5 >>
Only silicon powder was used as the negative electrode active material. Only silicon powder was treated with a vibrating ball mill in the same manner as in Example 1 to obtain a crystallite size of 12 nm. A negative electrode was produced in the same manner as in Example 1 except that this silicon powder was used. A battery E1 was produced in the same manner as in Example 1 except that this negative electrode was used.

<< Comparative Example 6 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E2 was produced in the same manner as in Example 2 except that this negative electrode was used.

<< Comparative Example 7 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E3 was produced in the same manner as in Comparative Example 1 except that this negative electrode was used.

<< Comparative Example 8 >>
Only SiO powder was used as the negative electrode active material. Only the SiO powder was treated with a vibration ball mill in the same manner as in Example 1 to obtain a crystallite size of 12 nm. A negative electrode was produced in the same manner as in Example 1 except that this SiO powder was used. A battery F1 was produced in the same manner as in Example 1 except that this negative electrode was used.

<< Comparative Example 9 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F2 was produced in the same manner as in Example 2 except that this negative electrode was used.

<< Comparative Example 10 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F3 was produced in the same manner as in Comparative Example 1 except that this negative electrode was used.

Manganese dioxide and lithium hydroxide were mixed at a molar ratio of 2: 1. The obtained mixture was calcined in the air at 500 ° C. for 24 hours to obtain LiMn ₂ O ₄ having an average particle diameter of 10 μm and a BET specific surface area of 16 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this LiMn ₂ O ₄ was used as the positive electrode active material. A battery A11 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 12. A battery B2 was produced in the same manner as in Example 10 except that this positive electrode was used.

  A positive electrode was produced in the same manner as in Example 12. A battery C2 was produced in the same manner as in Example 11 except that this positive electrode was used.

<< Comparative Example 11 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 12, except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when the battery voltage was discharged to 0 V) was 4.5 mAh, Battery D4 was produced.

<< Comparative Example 12 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E4 was produced in the same manner as in Example 12 except for the use of this negative electrode.

<< Comparative Example 13 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F4 was produced in the same manner as in Example 12 except for the use of this negative electrode.

Manganese dioxide and lithium hydroxide were mixed at a molar ratio of 1: 0.8. The obtained mixture was calcined in air at 500 ° C. for 6 hours to obtain Li ₄ Mn ₅ O ₁₂ having an average particle diameter of 10 μm and a BET specific surface area of 31 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this Li ₄ Mn ₅ O ₁₂ was used as a positive electrode active material. A battery A12 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 15. A battery B3 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 15. A battery C3 was produced in the same manner as in Example 11 except that this positive electrode was used.

<< Comparative Example 14 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 15 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when the battery voltage was discharged to 0 V) was 4.5 mAh, Battery D5 was produced.

<< Comparative Example 15 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E5 was produced in the same manner as in Example 15 except for the use of this negative electrode.

<< Comparative Example 16 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F5 was produced in the same manner as in Example 15 except for the use of this negative electrode.

MnCO ₃ and lithium hydroxide were mixed at a molar ratio of 2: 1. The obtained mixture was calcined in air at 345 ° C. for 32 hours to obtain Li ₂ Mn ₄ O ₉ having an average particle diameter of 10 μm and a BET specific surface area of 43 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this Li ₂ Mn ₄ O ₉ was used as a positive electrode active material. A battery A13 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 18. A battery B4 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 18. A battery C4 was produced in the same manner as in Example 11 except for the use of this positive electrode.

<< Comparative Example 17 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 18 except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D6 was produced.

<< Comparative Example 18 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E6 was produced in the same manner as in Example 18 except for the use of this negative electrode.

<< Comparative Example 19 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F6 was produced in the same manner as in Example 18 except for the use of this negative electrode.

MnCO ₃ , nickel hydroxide and lithium hydroxide were mixed at a molar ratio of 15: 5: 11. The obtained mixture was calcined in air at 345 ° C. for 32 hours to obtain Li _0.55 Mn _0.75 Ni _0.25 O ₂ having an average particle diameter of 10 μm and a BET specific surface area of 32 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this Li _0.55 Mn _0.75 Ni _0.25 O ₂ was used as the positive electrode active material. A battery A14 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 21. A battery B5 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 21. A battery C5 was produced in the same manner as in Example 11 except for the use of this positive electrode.

<< Comparative Example 20 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 21, except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D7 was produced.

<< Comparative Example 21 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E7 was produced in the same manner as in Example 21 except for the use of this negative electrode.

<< Comparative Example 22 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F7 was produced in the same manner as in Example 21 except for the use of this negative electrode.

MnCO ₃ , nickel hydroxide and lithium hydroxide were mixed at a molar ratio of 3: 1: 2. The obtained mixture was baked in air at 345 ° C. for 32 hours to obtain LiMn _1.5 Ni _0.5 O ₄ having an average particle diameter of 10 μm and a BET specific surface area of 38 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this LiMn _1.5 Ni _0.5 O ₄ was used as the positive electrode active material. A battery A15 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 24. A battery B6 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 24. A battery C6 was produced in the same manner as in Example 11 except for the use of this positive electrode.

<< Comparative Example 23 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 24, except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when the battery voltage was discharged to 0 V) was 4.5 mAh, Battery D8 was produced.

<< Comparative Example 24 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E8 was produced in the same manner as in Example 24 except for the use of this negative electrode.

<< Comparative Example 25 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F8 was produced in the same manner as in Example 24 except for the use of this negative electrode.

MnCO ₃ , nickel hydroxide and lithium hydroxide were mixed at a molar ratio of 3: 1: 3.2. The obtained mixture was calcined in air at 345 ° C. for 32 hours to obtain Li ₄ Mn _3.75 Ni _1.25 O ₁₂ having an average particle diameter of 10 μm and a BET specific surface area of 36 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this Li ₄ Mn _3.75 Ni _1.25 O ₁₂ was used as the positive electrode active material. A battery A16 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 27. A battery B7 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 27. A battery C7 was produced in the same manner as in Example 11 except for the use of this positive electrode.

<< Comparative Example 26 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 27, except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D9 was produced.

<< Comparative Example 27 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E9 was produced in the same manner as in Example 27 except for the use of this negative electrode.

<< Comparative Example 28 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F9 was produced in the same manner as in Example 27 except for the use of this negative electrode.

MnCO ₃ , nickel hydroxide and lithium hydroxide were mixed at a molar ratio of 3: 1: 2. The obtained mixture was calcined in air at 345 ° C. for 32 hours to obtain Li ₂ Mn ₃ NiO ₉ having an average particle diameter of 10 μm and a BET specific surface area of 25 m ² / g. A positive electrode was produced in the same manner as in Example 1 except that this Li ₂ Mn ₃ NiO ₉ was used as the positive electrode active material. A battery A17 was produced in the same manner as in Example 2 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 30. A battery B8 was produced in the same manner as in Example 10 except for the use of this positive electrode.

  A positive electrode was produced in the same manner as in Example 30. A battery C8 was produced in the same manner as in Example 11 except for the use of this positive electrode.

<< Comparative Example 29 >>
A negative electrode was produced in the same manner as in Comparative Example 2. Using this negative electrode, in the same manner as in Example 30, except that the amount of lithium foil was changed so that the initial discharge capacity at the time of deep discharge (when discharged to a battery voltage of 0 V) was 4.5 mAh, Battery D10 was produced.

<< Comparative Example 30 >>
A negative electrode was produced in the same manner as in Comparative Example 5. A battery E10 was produced in the same manner as in Example 30 except for the use of this negative electrode.

<< Comparative Example 31 >>
A negative electrode was produced in the same manner as in Comparative Example 8. A battery F10 was produced in the same manner as in Example 30 except for the use of this negative electrode.
The characteristics of each battery described above are shown in Tables 1-3.

For each battery described above, the capacity maintenance rate was evaluated by the following method.
In a constant temperature room set at 20 ° C., constant current charging / discharging is performed at 0.05 C (1 C is 1 hour rate current) for both charging current and discharging current, and battery voltage is 3.0 to 2.0 V (condition 1) or 50 cycles were repeated in the range of 3.0 to 0.0 V (condition 2).

  The ratio (percentage value) of the discharge capacity at the 50th cycle to the discharge capacity at the battery voltage of 3.0 to 2.0 V (condition 1) at the second cycle was determined as the capacity retention rate. The positive electrode potential and the negative electrode potential when the battery voltage was 2.0 V were also obtained.

The ratio (percentage value) of the discharge capacity at the 50th cycle to the discharge capacity at the battery voltage of 3.0 to 0.0V (condition 2) at the second cycle was determined as the capacity retention rate. The positive electrode potential and the negative electrode potential when the battery voltage was 0.0 V were also obtained.
The results are shown in Tables 4-6.

  FIG. 2 and FIG. 3 show the electrode potential with respect to metallic lithium at the time of initial discharge when the potential of the positive electrode and negative electrode when the battery voltage is 0 V is 1.8 V with respect to metallic lithium. However, for comparison of the shape of the discharge curves, the curves are standardized so that the battery capacities at the battery voltage of 0 V are the same.

FIG. 2 shows a discharge curve of a positive electrode whose positive electrode active material is Li _0.55 MnO ₂ or LiMn ₂ O ₄ , and a negative electrode whose negative electrode active material is graphite, silicon oxide, silicon-titanium alloy (Ti: Si = 15: 85). The discharge curve is shown.

FIG. 3 shows a discharge curve of the positive electrode in which the positive electrode active material is Li ₂ Mn ₄ O ₉ or LiMn _1.5 Ni _0.5 O ₄ , and the negative electrode active material is graphite, silicon oxide, silicon-titanium alloy (Ti: Si = 15: 85). ) Shows the discharge curve of the negative electrode.

2 and FIG. 3 show Example 2, Example 12, Example 18, Example 24, Comparative Example 3, Comparative Example 9, Comparative Example 11, Comparative Example 13, Comparative Example, and Comparative Example by arbitrarily combining the positive electrode and the negative electrode. 17 corresponds to the discharge curves of 12 kinds of batteries of Comparative Example 19, Comparative Example 23, and Comparative Example 25. For example, Comparative Example 3 corresponds to a combination of a Li _0.55 MnO ₂ positive electrode discharge curve and a graphite negative electrode discharge curve. In the case of Example 2, this corresponds to a combination of a Li _0.55 MnO ₂ positive electrode discharge curve and a silicon-titanium alloy negative electrode discharge curve.

The positive electrode discharge curve when the positive electrode active material is Li ₂ Mn ₄ O ₉ is the positive electrode when the positive electrode active material is Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₃ NiO ₉ or Li ₄ Mn _3.75 Ni _1.25 O ₁₂ Almost overlaps with the discharge curve. The negative electrode discharge curve when the negative electrode active material is silicon alone almost overlaps the discharge curve when the negative electrode active material is a silicon-titanium alloy. Therefore, FIG. 2 and FIG. 3 substantially show Comparative Example 3, Comparative Example 6, Comparative Example 9, Comparative Example 11 to Comparative Example 19, Comparative Examples 23 to 31, Example 2 to Example 20, and Example. This corresponds to a discharge curve at the time of initial discharge of 24-32 positive and negative batteries.

(I) Comparative Examples 2 to 4 In Comparative Examples 2 to 4, Li _0.55 MnO ₂ was used as the positive electrode active material and graphite was used as the negative electrode active material. The battery voltage is determined by the potential difference between the positive electrode and the negative electrode. When the battery voltage is 0.0 V, the potential of the positive electrode and the negative electrode in Comparative Example 2 is 2.0 V, the potential of the positive electrode and the negative electrode in Comparative Example 3 is 1.8 V, respectively. Each potential is 1.5V. At this time, the battery capacity is 4.5 mAh. The reason why the battery capacity is 4.5 mAh is that when the negative electrode active material is graphite, the capacity density per volume of the negative electrode becomes low. It is impossible to construct a battery with a design capacity of 7 mAh under the same conditions as in the example.

  When the cycle of cutting the discharge at a battery voltage of 2.0 V is repeated, Comparative Examples 2 to 4 show a relatively good capacity retention rate. However, when the cycle of cutting the discharge at a battery voltage of 0.0 V is repeated, the capacity retention rates of Comparative Examples 2 to 4 are lowered. This is because the negative electrode potential is repeated in the range of 0.25 V or more with respect to lithium, and graphite deteriorates.

  In Comparative Example 4, the potential of the positive electrode and the negative electrode with respect to metallic lithium at a battery voltage of 0 V is designed to be 1.5 V. In this case, when the cycle of cutting the discharge at a battery voltage of 0.0 V is repeated, the capacity retention rate is significantly reduced. This is because the positive electrode potential is repeated in the range of 1.8 V or less with respect to lithium, and the positive electrode active material deteriorates. In the case of Comparative Example 1, Comparative Example 7 and Comparative Example 10, the same tendency as in Comparative Example 4 is shown.

(Ii) Comparative Example 5 to Comparative Example 7 In Comparative Examples 5 to 7, Li _0.55 MnO ₂ was used as the positive electrode active material and silicon was used as the negative electrode active material. When silicon is used as the negative electrode active material, the capacity retention rate is relatively low even when the cycle of cutting discharge at a battery voltage of 2.0 V is repeated. This is because the volume change during charging / discharging of the negative electrode active material is large. In these comparative examples, it is considered difficult to maintain the current collecting structure in the electrode plate. When the cycle of cutting the discharge at a battery voltage of 0.0 V is repeated, the volume change of the negative electrode active material is further increased, and the capacity retention rate is also reduced.

(Iii) Comparative Example 8 to Comparative Example 10
In Comparative Examples 8 to 10, Li _0.55 MnO ₂ was used as the positive electrode active material and SiO was used as the negative electrode active material. When SiO is used, the volume change during charging / discharging of the active material is reduced as compared with the case where silicon is used. Nevertheless, when the cycle of cutting the discharge at a battery voltage of 0.0 V is repeated, the capacity retention rate decreases. As described above, this is due to the rapid increase in the amount of coating produced on the negative electrode active material surface. This is related to the fact that in the charged state, the negative electrode active material contains an alloy of lithium and silicon having a low electronic resistance, but in the deep discharge state, the electronic resistance of the alloy of lithium and silicon is remarkably increased.

(Iv) In the case of Examples 1 to 11 In Examples 1 to 11, Li _0.55 MnO ₂ was used as the positive electrode active material, and a silicon-transition metal alloy was used as the negative electrode active material. In these examples, even if the cycle of cutting the discharge at a battery voltage of 0.0 V is repeated, the decrease in the capacity retention rate is largely suppressed. As described above, this indicates that there is no rapid increase in the amount of film formed on the surface of the negative electrode active material, the low electronic resistance of the silicon-transition metal compound phase, and the increase in the electronic resistance of the negative electrode active material at the end of discharge. It is presumed to be related to what can be suppressed.

For example, a silicon-titanium alloy includes a silicon phase and a titanium disilicide phase having a low electronic resistance. The powder electronic resistance of the silicon-titanium alloy is 10 ⁻⁴ to 10 ⁻⁷ times that of silicon alone.
In Example 3, the weight ratio between the titanium disilicide phase and the silicon simple substance phase is 99: 1, assuming that all titanium forms titanium disilicide. Since the proportion of silicon alone is small, the capacity density per volume is low. Therefore, in Example 3, it designed so that the capacity | capacitance at the time of the battery voltage 0V might be 4.5 mAh.

In Example 8, the weight ratio of the titanium disilicide phase to the silicon simple substance phase is 7:93 assuming that all titanium forms titanium disilicide. Since the proportion of silicon alone is large, the volume change of the active material particles due to charge / discharge increases. Therefore, in Example 8, it is difficult to maintain the current collecting structure in the electrode plate. For this reason, when the cycle of cutting the discharge at the battery voltage of 0.0 V is repeated, the decrease in the capacity retention rate is slightly increased.
Examples 10 and 11 show that even when the transition metal is nickel or iron, the effect is almost the same as that of titanium.

(V) Other Examples and Comparative Examples LiMn ₂ O ₄ (Comparative Examples 11 to 13, Examples 12 to 14), Li ₄ Mn ₅ O ₁₂ (Comparative Examples 14 to Comparative Examples) were used as the positive electrode active material. 16, Example 15 to Example 17), Li ₂ Mn ₄ O ₉ (Comparative Example 17 to Comparative Example 19, Example 18 to Example 20), Li _0.55 Mn _0.75 Ni _0.25 O ₂ (Comparative Example 20 to Comparative Example) 22, Example 21 to Example 23), LiMn _1.5 Ni _0.5 O ₄ (Comparative Example 23 to Comparative Example 25, Example 24 to Example 26), Li ₄ Mn _3.75 Ni _1.25 O ₁₂ (Comparative Example 26 to Comparative Example) 28, Example 27 to Example 29), Li ₂ Mn ₃ NiO ₉ (Comparative Example 29 to Comparative Example 31, Example 30 to Example 32), Li _0.55 MnO ₂ (Comparative Example 2 to Comparative) The same results as in Example 10 and Examples 1 to 11) were obtained.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having a high capacity and an excellent deep discharge cycle life.

It is a longitudinal cross-sectional view of the coin-type battery which concerns on the Example of this invention. It is a figure which shows the electric potential change with respect to metallic lithium in the first time discharge of a positive electrode and a negative electrode. It is another figure which shows the electric potential change with respect to metallic lithium in the first time discharge of a positive electrode and a negative electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator

Claims (8)

Comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte;
The positive electrode includes a positive electrode active material including a lithium-containing manganese oxide,
The negative electrode includes a negative electrode active material that is an alloy of silicon and a transition metal element,
The transition metal element is at least one selected from the group consisting of titanium, nickel and iron;
A non-aqueous electrolyte secondary battery in which the potential of the positive electrode and the negative electrode at a battery voltage of 0 V is 1.8 V or more with respect to metallic lithium (Li / Li ⁺ ). The non-lithium according to claim 1, wherein the lithium-containing manganese oxide includes at least one selected from the group consisting of Li _0.55 MnO ₂ , LiMn ₂ O ₄ , Li ₄ Mn ₅ O ₁₂ and Li ₂ Mn ₄ O _9. Water electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a molar ratio between the silicon and the transition metal element is 67:33 to 98: 2.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a molar ratio between the silicon and the transition metal element is 74:26 to 95: 5.   2. The nonaqueous electrolyte according to claim 1, wherein a part of manganese in the lithium-containing manganese oxide is substituted with an element Me, and the element Me is at least one selected from the group consisting of nickel and iron. Secondary battery. The nonaqueous electrolyte secondary battery according to claim 5 , wherein a molar ratio of the element Me to manganese in the lithium-containing manganese oxide is 1/3 or less.   The non-aqueous solution according to claim 1, wherein the negative electrode includes a molded body of a negative electrode mixture, the negative electrode mixture includes the negative electrode active material, and the thickness of the molded body is 0.05 mm to 2.0 mm. Electrolyte secondary battery.   The non-aqueous solution according to claim 1, wherein the positive electrode includes a molded body of a positive electrode mixture, the positive electrode mixture includes the positive electrode active material, and the thickness of the molded body is 0.30 mm to 3.0 mm. Electrolyte secondary battery.

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