JP5006599B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, and more particularly to improving the safety of a lithium ion secondary battery.

  Lithium ion secondary batteries are used as a main power source for many mobile communication devices and portable electronic devices because of their high voltage and high energy density. In recent years, these devices have been reduced in size and performance, and accordingly, further increase in energy density of lithium ion secondary batteries has been demanded.

  As the energy density of lithium ion secondary batteries increases, the importance of ensuring the thermal stability of lithium ion secondary batteries is increasing. For example, when an amount of electricity exceeding the rated capacity is charged due to equipment trouble and the lithium ion secondary battery is overcharged or when an internal short circuit occurs, the lithium ion secondary battery may generate heat. . The temperature rise is greatest at locations where an internal short circuit occurs and at the center of the battery. However, the battery surface may also rise in temperature due to the influence inside the battery.

  From the viewpoint of improving the thermal stability of the lithium ion secondary battery, studies have been made to improve the constituent materials of the battery. In general, in a charged lithium ion secondary battery, the thermal stability of the electrode active material is lowered, and in particular, the thermal stability of the positive electrode active material is greatly lowered.

  The mechanism by which the battery generates heat is generally considered as follows. First, when the temperature inside the battery rises and becomes higher than the heat generation start temperature of the positive electrode with low thermal stability, the positive electrode starts to generate heat. Due to the heat generation of the positive electrode, the temperature inside the battery further rises and reaches the heat generation start temperature of the negative electrode. When the negative electrode starts to generate heat, the temperature inside the battery further increases.

Therefore, for example, when a lithium ion secondary battery is overcharged due to a trouble with a charging device, the temperature inside the battery is significantly increased, and as a result, the temperature of the battery surface may also be increased.
Based on the above, it is considered that the thermal stability of the battery is also improved by improving the thermal stability of the positive electrode active material that first starts to generate heat. Thus, it has been proposed to increase the thermal stability of the positive electrode active material in a charged state (see Patent Documents 1 and 2).
JP 2001-52684 A JP 2003-132883 A

  However, simply improving the positive electrode makes it difficult to control the subsequent temperature rise when the temperature inside the battery reaches the heat generation start temperature of the positive electrode.

The present invention includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, and a temperature T _{1 at} which the rate of heat generation in the charged state of the positive electrode is maximized. , the difference between the temperature T ₂ of heat release rate in the charged state of the negative electrode is maximized: [Delta] T is state, and are 50 ° C. or more, T ₁ <T _2, and the temperature T ₁ is 215 ° C. or higher, the temperature T ₂ Ru der less 295 ° C., a lithium ion secondary battery.

The positive electrode active material is preferably a powdered material in terms of ease of electrode production and reaction area. The positive electrode preferably includes a positive electrode active material, a conductive agent, and a binder in terms of conductivity and strength. The positive electrode active material is Li _x Co _1-yz Ni _y M _z O ₂ (0.95 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.9, and 0 ≦ z ≦ 0 in terms of charge / discharge capacity. .5, and the element M is preferably at least one selected from the group consisting of Al, Mn, Mg, Ti, V, Fe, Cu, and Zn.

  The negative electrode active material is preferably a powdered material in terms of ease of electrode production and reaction area. The negative electrode preferably contains a negative electrode active material and a binder in terms of strength. The negative electrode active material preferably includes at least one selected from the group consisting of a carbon material, Si, Si alloy, Si oxide, Sn, Sn alloy, and Sn oxide in terms of charge / discharge capacity.

The temperature T ₁ and the temperature T ₂ can be obtained by ARC measurement (Accelerating Rate Calorimetry) of the positive electrode and the negative electrode taken out from the charged battery, respectively. A battery in a charged state refers to a battery that is charged by a charger until the battery voltage reaches a charge end voltage (upper limit voltage for charging the battery).

The present invention further includes a lithium ion secondary battery and a charger for charging the lithium ion secondary battery, the lithium ion secondary battery includes a positive electrode capable of inserting and extracting lithium, and inserting and extracting lithium. A rechargeable negative electrode and a non-aqueous electrolyte, and the charger has a function of terminating charging when the lithium ion secondary battery is in a charged state of 90% or more of the rated capacity. The temperature T _{1 at} which the rate of heat generation of the positive electrode in the lithium ion secondary battery that is in a charged state of 90% or more of the capacity becomes the maximum, and the negative electrode in the lithium ion secondary battery that is in the charged state of 90% or more of the rated capacity the difference between the temperature T ₂ where the heating rate is maximum: [Delta] T is state, and are 50 ° C. or more, T ₁ <T _2, and the temperature T ₁ is 215 ° C. or higher, der temperature T ₂ is 295 ° C. or less Rechargeable lithium-ion battery charging system .

  ADVANTAGE OF THE INVENTION According to this invention, the raise of the surface temperature of the lithium ion secondary battery which is an overcharge state can be suppressed.

In an overcharged lithium ion secondary battery, it is considered that the temperature inside the battery rises for the following reason.
In the overcharged state, the electrochemical reactivity of the electrode active material decreases and the internal resistance of the battery increases, so Joule heat is generated. When the temperature inside the battery rises due to Joule heat and becomes higher than the heat generation start temperature of the positive electrode having low thermal stability, the positive electrode starts to generate heat. Due to the heat generation of the positive electrode, the temperature inside the battery further rises and reaches the heat generation start temperature of the negative electrode. When the negative electrode starts to generate heat, the temperature inside the battery further increases.

  In a lithium ion secondary battery in a charged state, the thermal stability of the positive electrode is lower than that of the negative electrode, and the positive electrode generates heat first. Therefore, the thermal stability of the whole battery can be improved by increasing the thermal stability of the positive electrode. However, when the temperature inside the battery becomes equal to or higher than the heat generation start temperature of the positive electrode due to Joule heat, the subsequent heat generation of the positive electrode and the negative electrode cannot be suppressed.

In order to clarify the relationship between the heat generation temperatures of the positive electrode and the negative electrode and the thermal stability of the battery, the present inventors conducted the following examination.
First, overcharge tests were performed on batteries of various configurations at a low temperature (0 ° C.) with a current value of 1C (a current value that charges or discharges the amount of electricity corresponding to the rated capacity in one hour), and the surface of the battery The temperature was measured. Further, the positive electrode and the negative electrode were taken out from the charged battery, and the thermal behavior in the charged state of the positive electrode and the negative electrode was measured with an ARC apparatus (Accelerating Rate Calorimeter). Then, a temperature T ₁ at which the heat generation rate in the charged state of the positive electrode is maximized and a temperature T ₂ at which the heat generation rate in the charged state of the negative electrode is maximized were obtained. As a result, when the difference between the temperature T ₁ and the temperature T ₂ : ΔT is 50 ° C. or higher, even if overcharging is performed at a current value of 1 C at 0 ° C., the surface temperature of the battery is suppressed to 60 ° C. or lower. Found that is possible.

Therefore, the present invention includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte, and a temperature T at which the rate of heat generation in the charged state of the positive electrode is maximized. difference _1, a temperature T ₂ where the heating rate in the charged state of the negative electrode is maximized: [Delta] T is at 50 ° C. or higher, it proposes a lithium ion secondary battery. From the viewpoint of significantly suppressing an increase in the surface temperature of the lithium ion secondary battery that is in an overcharged state, ΔT is preferably 55 ° C. or higher.

Temperatures T ₁ is a 2 15 ° C. or more, preferably 250 ° C. or higher. By setting the temperature T ₁ to 215 ° C. or higher, the surface temperature of the battery during overcharging can be further reduced.
The temperature T ₂ is 295 ° C. or lower, for example, preferably 265 ° C. or higher. By setting the temperature T ₂ to 265 ° C. or higher, the surface temperature of the battery during overcharging can be further reduced.

  From the viewpoint of safety, when performing an overcharge test (a test for charging up to 150% of the rated capacity) at 0 ° C and a current value of 1C, the maximum surface temperature of the battery is 60 ° C or less It is preferable that A battery whose surface temperature exceeds 60 ° C. in the overcharge test at 0 ° C. reaches a considerably high temperature when overcharged at room temperature. Therefore, there is a possibility that a problem such as a failure occurs in a device using the battery. For example, the battery may be overcharged at room temperature due to a malfunction of the control circuit.

A battery whose surface temperature does not exceed 60 ° C. in the overcharge test at 0 ° C. does not reach that high temperature even if the battery is overcharged at room temperature. Therefore, the malfunction of the apparatus by the battery temperature rise can be avoided.
In the present invention, for example, the following positive electrode, negative electrode, and nonaqueous electrolyte can be used.

(I) Positive electrode A positive electrode contains a positive electrode active material, a electrically conductive agent, and a binder, for example. The positive electrode active material is Li _x Co _1-yz Ni _y M _z O ₂ (0.95 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.9, and 0 ≦ z ≦ 0.5, and the element M Is preferably at least one selected from the group consisting of Al, Mn, Mg, Ti, V, Fe, Cu and Zn.).

The form of the lithium composite oxide is not particularly limited. For example, the active material particles may be formed in a primary particle state, or the active material particles may be formed in a secondary particle state. A plurality of active material particles may be aggregated to form secondary particles. Although the average particle diameter of the active material particles is not particularly limited, for example, 1 to 30 μm is preferable, and 10 to 30 μm is particularly preferable. The average particle diameter can be measured by, for example, a wet laser diffraction particle size distribution measuring device manufactured by Microtrack. In this case, the 50% value (median value: D ₅₀ ) on the volume basis can be regarded as the average particle diameter of the active material particles.

  The element M in the lithium composite oxide is preferably at least one selected from the group consisting of Mn, Al, Mg, Ti, V, Fe, Cu, and Zn. These elements may be included alone as the element M in the lithium composite oxide, or two or more of them may be included. Among these, Mn, Al, Mg and the like are particularly preferable in that the effect of improving the thermal stability of the lithium composite oxide can be obtained.

The range of x representing the Li content increases or decreases depending on the charge / discharge of the battery, but the range of x in the initial state (immediately after the synthesis of the lithium composite oxide) is generally 0.95 ≦ x ≦ 1.1.
The range of y representing the Ni content is preferably, for example, 0 ≦ y ≦ 0.9 or 0.3 ≦ y ≦ 0.85. By using a positive electrode active material containing Ni, a high capacity can be realized.

The atomic ratio a of Co to the total of Co, Ni, and element M is preferably 0.05 ≦ a ≦ 0.5, and more preferably 0.05 ≦ a ≦ 0.35.
When the element M contains Al, the atomic ratio b of Al with respect to the total of Co, Ni, and the element M is preferably 0.005 ≦ b ≦ 0.1, and 0.01 ≦ b ≦ 0.08. More preferably.
When the element M includes Mn, the atomic ratio c of Mn with respect to the total of Co, Ni, and the element M is preferably 0.005 ≦ c ≦ 0.5, and 0.01 ≦ c ≦ 0.35. More preferably.
When the element M contains Mg, the atomic ratio d of Mg to the total of Co, Ni, and element M is preferably 0.00002 ≦ d ≦ 0.1, and 0.0001 ≦ d ≦ 0.05. More preferably.

  The conductive agent included in the positive electrode may be any electron-conductive material that is chemically stable in the battery. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, expanded graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber Conductive fibers such as can be used. These may be used alone or in combination of two or more. Among these, carbon black is preferable, and acetylene black is particularly preferable in terms of fine particles and high conductivity. The amount of the conductive agent is preferably 2 to 15 parts by weight or 3 to 10 parts by weight per 100 parts by weight of the positive electrode active material.

  The binder to be included in the positive electrode may be any resin that can be generally used as a binder for the positive electrode of a lithium ion secondary battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) ), Styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride- Chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoro Ethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene -Acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, etc. are mentioned. These may be used alone or in combination of two or more. These may be cross-linked products of Na ions or the like. PTFE is preferable from the viewpoint that a good electrode strength can be obtained without inhibiting the electrode reaction.

  The method for producing the positive electrode and the shape of the positive electrode are not particularly limited. Generally, a positive electrode is produced by supporting a positive electrode mixture containing a positive electrode active material, a conductive agent, and a binder on a belt-shaped positive electrode current collector. The positive electrode mixture can be supported on the positive electrode current collector by preparing a slurry by dispersing the positive electrode mixture in a liquid component, applying the slurry to the positive electrode current collector, and drying the slurry. The positive electrode mixture can be formed into a sheet or pellet to produce a positive electrode.

  For the positive electrode current collector, for example, a foil or a sheet containing aluminum, stainless steel, nickel, titanium, or the like can be used. Aluminum foil, aluminum alloy foil, and the like are particularly preferable in terms of cost, workability, stability, and the like. A carbon or titanium layer or an oxide layer can be formed on the surface of the foil or sheet. Unevenness can also be imparted to the surface of the foil or sheet. A net, a punching sheet, a lath body, a porous body, a foamed body, and the like can also be used. The positive electrode current collector may be one in which a conductive layer is formed on the surface of a resin sheet that does not have electronic conductivity. As a material for the resin sheet, polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, or the like is used. Although the thickness of a positive electrode electrical power collector is not specifically limited, For example, it is 1-500 micrometers.

(Ii) Negative electrode A negative electrode contains a negative electrode active material and a binder, for example. The negative electrode active material may be a material capable of electrochemically charging and discharging lithium, such as a carbon material, a metal, an alloy, and a metal oxide. An alloy is preferable in terms of charge / discharge capacity and cycle characteristics.

Examples of the carbon material include natural graphite, artificial graphite, non-graphitizable carbon, and the like.
As the metal and alloy, for example, silicon simple substance, silicon alloy, tin simple substance, tin alloy, germanium simple substance, germanium alloy and the like can be used. Of these, silicon alone and silicon alloys are particularly preferable. The metal element other than silicon contained in the silicon alloy is preferably a metal element that does not form an alloy with lithium. The metal element that does not form an alloy with lithium may be a chemically stable electron conductor, but is preferably titanium, copper, nickel, or the like. One of these may be contained alone in the silicon alloy, or a plurality of these may be contained in the silicon alloy at the same time.

  When the silicon alloy contains Ti, the molar ratio of Ti / Si is preferably 0 <Ti / Si <2, and particularly preferably 0.1 ≦ Ti / Si ≦ 1.0. When the silicon alloy contains Cu, the Cu / Si molar ratio is preferably 0 <Cu / Si <4, and particularly preferably 0.1 ≦ Cu / Si ≦ 2.0. When the silicon alloy contains Ni, the Ni / Si molar ratio is preferably 0 <Ni / Si <2, particularly preferably 0.1 ≦ Ni / Si ≦ 1.0.

As the metal oxide, for example, silicon oxide, tin oxide, germanium oxide, or the like can be used. Of these, silicon oxide is particularly preferable. The silicon oxide desirably has a composition represented by the general formula SiO _x (0 <x <2). Here, the x value indicating the content of oxygen element is more preferably 0.01 ≦ x ≦ 1.

  The binder contained in the negative electrode may be any resin that can be used for the negative electrode binder of a lithium ion secondary battery. For example, styrene butadiene rubber (SBR), polyethylene, polypropylene, polytetrafluoroethylene (PTFE). ), Polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, fluorine Vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-te Lafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer , Ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, and the like. These may be used alone or in combination of two or more. These may be cross-linked products of Na ions or the like. SBR is particularly preferable in terms of binding force. SBR may contain another monomer unit in addition to the styrene unit and the butadiene unit.

  The negative electrode can also contain a conductive agent. The conductive agent contained in the negative electrode may be any electron conductive material that is chemically stable in the battery. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, expanded graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber Conductive fibers such as can be used. These may be used alone or in combination of two or more. Among these, carbon black is preferable, and acetylene black is particularly preferable in terms of fine particles and high conductivity. The amount of the conductive agent is preferably, for example, 2 to 15 parts by weight or 3 to 10 parts by weight per 100 parts by weight of the negative electrode active material.

  The method for producing the negative electrode and the shape of the negative electrode are not particularly limited. Generally, a negative electrode is produced by supporting a negative electrode mixture containing a negative electrode active material, a binder, and, if necessary, a conductive agent on a strip-shaped negative electrode current collector. The negative electrode mixture can be supported on the negative electrode current collector by preparing a slurry by dispersing the negative electrode mixture in a liquid component, applying the slurry to the negative electrode current collector, and drying the slurry. A negative electrode can also be produced by forming the negative electrode mixture into a sheet or pellet.

  For the negative electrode current collector, for example, a foil or a sheet containing stainless steel, nickel, copper, titanium, or the like can be used. In terms of cost, workability, stability, etc., copper foil and copper alloy foil are particularly preferable. On the surface of the foil or sheet, a layer of carbon, titanium, nickel or the like can be provided, or an oxide layer can be formed. Unevenness can also be imparted to the surface of the foil or sheet. A net, a punching sheet, a lath body, a porous body, a foamed body, and the like can also be used. The negative electrode current collector may be one in which a conductive layer is formed on the surface of a resin sheet that does not have electronic conductivity. As a material for the resin sheet, polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, or the like is used. Although the thickness of a negative electrode collector is not specifically limited, For example, it is 1-500 micrometers.

For the non-aqueous electrolyte, a non-aqueous solvent in which a lithium salt is dissolved is preferably used.
Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), cyclic carbonates such as butylene carbonate (BC), 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, γ-butyrolactone, γ-valerolactone, etc. Lactones, chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, Dimethyl sulfoxide, 1,3 -Dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolide Non, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, and N-methyl-2-pyrrolidone can be used. These may be used alone, but it is preferable to use a mixture of two or more. Among these, a mixed solvent of a cyclic carbonate and a chain carbonate, or a mixed solvent of a cyclic carbonate, a chain carbonate, and an aliphatic carboxylic acid ester is preferable.

Examples of the lithium salt dissolved in the non-aqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , Examples include LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, lithium imide salt, and the like. These may be used alone or in combination of two or more, but at least LiPF ₆ is preferably used. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but the lithium salt concentration is preferably 0.2 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L.

  Various additives can be added to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics of the battery. As the additive, for example, at least one selected from the group consisting of vinylene carbonate, vinyl ethylene carbonate, phosphazene and fluorobenzene is preferably used. Appropriate amounts of these additives are 0.5 to 20% by weight of the non-aqueous electrolyte.

  In general, it is necessary to interpose a separator between the positive electrode and the negative electrode. As the separator, a microporous thin film having a large ion permeability, a predetermined mechanical strength, and an insulating property is preferably used. The microporous thin film preferably has a function of closing the pores at a certain temperature or higher and increasing the resistance. As the material of the microporous thin film, polyolefin such as polypropylene and polyethylene having excellent organic solvent resistance and hydrophobicity is preferably used. A sheet made from glass fiber or the like, a nonwoven fabric, a woven fabric, or the like is also used. The pore diameter of the separator is, for example, 0.01 to 1 μm. The thickness of the separator is generally 10 to 300 μm. The porosity of the separator is generally 30 to 80%.

The structure of the lithium ion secondary battery of the present invention is not particularly limited, and the present invention can be applied without particular limitation as long as the battery has a structure in which a positive electrode and a negative electrode are opposed to each other via a separator or an electrolyte. . Examples of the shape of the battery include a coin shape, a sheet shape, a cylindrical shape, and a square shape. The lithium ion secondary battery of the present invention may be a large size used for an electric vehicle or the like, or a small size used for a portable information terminal, a portable electronic device, or the like. The lithium ion secondary battery of the present invention can also be used for small household power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, and the like.
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

  Various positive electrodes and negative electrodes were prepared, and 18650 size cylindrical lithium ion secondary batteries as shown in FIG. 1 were manufactured using them.

(I) Production of positive electrode Lithium hydroxide powder, cobalt hydroxide powder, nickel hydroxide powder, aluminum hydroxide powder, and trimanganese tetraoxide powder were blended at a predetermined ratio, and the resulting mixture was mixed with 800 in an oxygen atmosphere. A positive electrode active material which is fired at 0 ° C. and made of various lithium-containing composite oxides (LiCoO ₂ , LiCo _0.2 Ni _0.8 O ₂ , LiCo _0.15 Ni _0.8 Al _0.05 O ₂ , and LiCo _0.33 Ni _0.33 Mn _0.33 O ₂ ) shown in Table 1 (average particle size D ₅₀ are all 10 [mu] m) was prepared.

  A positive electrode active material, an acetylene black (AB) as a conductive agent, and an aqueous emulsion of polytetrafluoroethylene (PTFE) as a binder so that the positive electrode active material: AB: PTFE has a predetermined weight ratio. Then, water was added as a dispersion medium and kneaded to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector (thickness 20 μm) made of aluminum foil with a comma coater type coating machine, dried, and then rolled with a roller to prepare a positive electrode sheet. The positive electrode sheet was cut into a predetermined size, processed, and the positive electrode lead 4 was welded to obtain the positive electrode 1.

(Ii) Production of Negative Electrode Various materials shown in Table 1 (artificial graphite, Ti—Si alloy, Si simple substance, Sn simple substance, SiO, and SnO) were used as the negative electrode active material. Ti-Si alloy, Si simple substance, Sn simple substance, SiO, and SnO are all manufactured by Kojundo Chemical Laboratory. The Ti—Si alloy was prepared by a mechanical alloying method. The contents of Ti and Si in the Ti—Si alloy were 37 wt% and 63 wt%, respectively. The obtained Ti—Si alloy was a two-phase alloy containing a TiSi ₂ phase and a Si single phase. Each negative electrode active material had a maximum particle size of 50 μm and an average particle size D ₅₀ of 20 μm.

  A negative electrode active material, acetylene black (AB) as a conductive agent, and an aqueous emulsion of styrene butadiene rubber (SBR) as a binder are blended so that the negative electrode active material: AB: SBR has a predetermined weight ratio. Then, water was added as a dispersion medium and kneaded to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector (thickness 15 μm) made of copper foil with a comma coater type coating machine, dried, and then rolled with a roller to prepare a negative electrode sheet. The negative electrode sheet was cut into a predetermined size, processed, and the negative electrode lead 5 was welded to obtain the negative electrode 2.

(Iii) Preparation of non-aqueous electrolyte Ethylene carbonate and ethyl methyl carbonate, which are non-aqueous solvents, were mixed at a volume ratio of 1: 1, and 1 mol of lithium hexafluorophosphate (LiPF ₆ ) was added to the obtained mixed solvent. A nonaqueous electrolyte was obtained by dissolving at a concentration of 1 liter.

(Iv) Production of Battery The positive electrode 1 and the negative electrode 2 were wound together with the separator 3 interposed between them to produce an electrode group. As the separator 3, a polyethylene microporous film (manufactured by Tonen Chemical Co., Ltd.) having a thickness of 25 μm was used. This electrode group was inserted into the battery case 8 together with the upper insulating plate 6 and the lower insulating plate 7 disposed above and below the electrode group. The positive electrode lead 4 was welded to the lower surface of the sealing plate 9 having the positive electrode terminal 10, and the negative electrode lead 5 was welded to the inner bottom surface of the battery case 8. Thereafter, a non-aqueous electrolyte was poured into the battery case 8, and the opening of the battery case 8 was sealed with the sealing plate 9 to complete the battery. The design capacity of all batteries was 2000 mAh. The voltage range of charging / discharging was 4.3V-2.5V.

(V) ARC measurement Each battery was charged to a battery voltage of 4.3 V with a constant current of 1 C. Thereafter, the battery was charged at a constant voltage of 4.3 V until the current value reached 0.05 C (100 mA). In any battery, when the battery voltage is 4.3 V, the capacity balance between the positive electrode and the negative electrode is adjusted so that the positive electrode potential with respect to lithium metal is 4.25 V and the negative electrode potential is 0.05 V. did. In addition, it was confirmed that the capacity at this time was 100% of the rated capacity.
In a dry air atmosphere with a dew point of −50 ° C., the positive electrode and the negative electrode were taken out from the charged battery and sealed in a sealed container.

ARC measurement was performed using the enclosed sample, and a temperature T _{1 at} which the heat generation rate of the positive electrode was maximized and a temperature T ₂ at which the heat generation rate of the negative electrode was maximized were determined. The results are shown in Table 1.
As the ARC measuring device, a device manufactured by Thermal Hazard Technology was used. The measurement conditions are shown below.
Temperature Step: 20 ℃
Wait Time: 15 minutes
Temp. Rate Sensitivity: 0.04 ℃ / min
Calculation Step temp .: 0.2 ℃

表１に示した正極と負極とを、表２に示す様々な組み合わせで用いて、電池１〜２２を作製した。電池３、４、９、１３、１６および１８は、Ｔ₁とＴ₂との差：ΔＴが５０℃未満であり、比較例に相当する。電池１、２、５、６、７、１０、１１、１４および１５は、Ｔ ₁ が２１５℃未満であり、参考例に相当する。その他の電池は、Ｔ₁とＴ₂との差：ΔＴが５０℃以上であり、実施例に相当する。

Batteries 1 to 22 were produced using the positive electrode and negative electrode shown in Table 1 in various combinations shown in Table 2. Batteries 3, 4, 9, 13, 16 and 18 have a difference between T ₁ and T ₂ : ΔT of less than 50 ° C. and correspond to a comparative example. Batteries 1, 2, 5, 6, 7, ₁₀ , 11, 14, and 15 have T ₁ of less than 215 ° C. and correspond to reference examples. Other batteries have a difference between T ₁ and T ₂ : ΔT of 50 ° C. or more, which corresponds to the example.

  A thermocouple was attached to the surface of each battery, and an overcharge test (a test for charging up to 150% of the rated capacity) was performed at a current value of 1 C at 0 ° C. Table 3 shows the maximum reached temperature of the surface temperature of the battery.

As shown in Table 2 and Table 3, when ΔT obtained by ARC measurement of the positive electrode and the negative electrode is 50 ° C. or higher, the maximum temperature reached on the battery surface is suppressed to 60 ° C. or lower. Among batteries having the same ΔT, when the temperature T _{1 at} which the heat generation rate of the positive electrode is maximum is 215 ° C. or higher, the maximum temperature reached on the battery surface is lower, for example, 55 ° C. or lower. Yes.
On the other hand, when ΔT was less than 50 ° C., the maximum temperature reached on the battery surface exceeded 60 ° C.

In this example, LiCoO ₂ , LiCo _0.2 Ni _0.8 O ₂ , LiCo _0.15 Ni _0.8 Al _0.05 O ₂ , and LiCo _0.33 Ni _0.33 Mn _0.33 O ₂ were used as the positive electrode active material, and artificial graphite, Ti Although -Si alloy, Si simple substance, Sn simple substance, SiO, and SnO were used, the same result can be obtained even if other active materials are used.

  The lithium ion secondary battery of the present invention has a high energy density and excellent stability. The use of the lithium ion secondary battery of the present invention is not particularly limited, but is particularly useful as a power source for portable devices such as mobile phones and notebook computers.

It is a longitudinal cross-sectional view of an example of the lithium ion secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Upper insulating plate 7 Lower insulating plate 8 Battery case 9 Sealing plate 10 Positive terminal

Claims (4)

A positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte,
The difference between the temperatures T ₁ where the heating rate in the state of charge of the positive electrode is maximized, and the temperature T ₂ of heat release rate in the charged state of the negative electrode is maximized: [Delta] T is state, and are 50 ° C. or higher,
T ₁ <T ₂ and
The temperature T ₁ is 215 ° C. or higher,
Temperature T ₂ is Ru der 295 ° C. or less, a lithium ion secondary battery. The positive electrode comprises a positive electrode active material, conductive agent, and, a binder, wherein the positive electrode active _{material, Li x Co 1-yz Ni} y M z O 2 (0.95 ≦ x ≦ 1.1,0 ≦ y ≦ 0.9 and 0 ≦ z ≦ 0.5 are satisfied, and the element M is at least one selected from the group consisting of Al, Mn, Mg, Ti, V, Fe, Cu, and Zn The lithium ion secondary battery of Claim 1 represented by this.   The negative electrode includes a negative electrode active material and a binder, and the negative electrode active material is at least selected from the group consisting of a carbon material, Si, Si alloy, Si oxide, Sn, Sn alloy, and Sn oxide. The lithium ion secondary battery of Claim 1 containing 1 type. A lithium ion secondary battery and a charger for charging the lithium ion secondary battery,
The lithium ion secondary battery has a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte,
The charger has a function of terminating charging when the lithium ion secondary battery is in a charged state of 90% or more of the rated capacity;
The temperature T _{1 at} which the heat generation rate of the positive electrode in the lithium ion secondary battery in a charged state of 90% or more of the rated capacity is maximized, and the lithium ion secondary battery in a charged state of 90% or more of the rated capacity the difference in heat release rate of the negative electrode and the temperature T ₂ which is a maximum: [Delta] T is state, and are 50 ° C. or higher,
T ₁ <T ₂ and
The temperature T ₁ is 215 ° C. or higher,
Temperature T ₂ is Ru der 295 ° C. or less, the charging system of the lithium ion secondary battery.

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