JP5095098B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using lithium ions, and more particularly to a non-aqueous electrolyte secondary battery that operates at a high voltage with a suitable positive electrode active material.

In recent years, non-aqueous electrolyte secondary batteries used as a main power source for mobile communication devices and portable electronic devices have a high electromotive force and a high energy density. Examples of the positive electrode active material used here include lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ). These active materials have a potential of 4 V or more with respect to lithium (Li).

In a lithium ion secondary battery using these active materials, when the battery charging voltage is increased, the capacity is increased by that amount. Therefore, a higher operating voltage has been studied.
Among these, lithium spinel oxide containing manganese (Mn) is stable even at a high potential, and therefore, a proposal has been made to set the upper limit charging voltage in the range of 4.0 V to 4.5 V (see, for example, Patent Document 1). .
Moreover, lithium composite cobalt oxides mainly used have a high capacity and are excellent in various characteristics such as cycle characteristics and storage characteristics. However, since it is inferior in thermal stability and deteriorates by repeated charging and discharging at a high voltage, the charging end voltage is 4.2 V at most (4.25 V including the error of the control circuit) in a normal operating state. It was. When operating at a voltage higher than this, there was a problem in safety in particular.

Even if the end-of-charge voltage is set to 4.2 V, the battery voltage may increase if an overcharge state occurs due to an accident or the like. In view of this, in order to stably maintain the crystal structure of the positive electrode active material even in an overcharged state, a technique in which a specific element is dissolved in a composite oxide has been proposed (see, for example, Patent Document 2). There is also a proposal aimed at improving the thermal stability of a battery during overcharging by mixing two specific active materials (see, for example, Patent Document 3).
JP 2001-307781 A JP 2002-203553 A JP 2002-319398 A

  When the end-of-charge voltage in the normal operating state is set to 4.25 V or more, the utilization rate of the positive electrode, that is, the capacity increases, but the negative electrode load is constant. If applied as it is, the battery capacity is unbalanced.

  The present invention solves this problem, and even if the end-of-charge voltage in a normal operating state is set to 4.25 V or more, the battery functions such as cycle characteristics, heat resistance, and storage characteristics normally operate as well as safety. An object of the present invention is to provide a high-capacity nonaqueous electrolyte secondary battery.

  When the end-of-charge voltage in the normal operating state is set to various values of 4.25 V or more, if the positive and negative electrode weights are set to constant values as in the conventional case, the capacity balance between the positive electrode and the negative electrode is lost, and the characteristics deteriorate. . In order to maintain the battery capacity balance, it is effective to reduce the weight of the positive electrode and increase the weight of the negative electrode. Furthermore, the positive and negative active materials have different loads (capacity per weight) depending on the position of the electrode plate between the portion facing the counter electrode and the portion not.

In view of the above, the present invention provides a positive electrode containing a lithium composite oxide as an active material, and a non-aqueous electrolyte secondary battery in which a charge end voltage is set to 4.4 to 4.5 V. The weight ratio R of the active material per unit area included in each of the positive electrode and the negative electrode in the opposing regions is set to a specific value.
That is, the non-aqueous electrolyte secondary battery of the present invention includes a negative electrode including an active material capable of inserting and extracting lithium, a positive electrode including a lithium composite oxide as an active material, a separator separating the negative electrode and the positive electrode, and lithium ions A non-aqueous electrolyte secondary battery comprising a conductive non-aqueous electrolyte and having an end-of-charge voltage set to 4.4 to 4.5 V, wherein the positive electrode and the negative electrode are opposed to each other in a region facing each other. The ratio R = Wp / Wn between the weight Wp per unit area of the active material contained and the weight Wn per unit area of the active material contained in the negative electrode is in the range of 1.3 to 19.
The lithium composite oxide is oxide A, oxide B, or a mixture of oxide A and oxide B, and oxide A has the formula Li _x Co _{1- y My} O ₂ (M is Mg, Al At least one selected from the group consisting of Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba There is represented by a 1.0 ≦ x ≦ 1.15,0.005 ≦ y ≦ 0.1.), oxide B has the formula _{Li x Ni y Mn z M 1} -yz O 2 (M is It is at least one selected from the group consisting of Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, and Re, and 1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 0.5, and 0.9 ≦ y / z ≦ 3.0.
In one aspect of the present invention, the active material of the negative electrode is mainly a carbonaceous material , the lithium composite oxide is a mixture of oxide A and oxide B, and the weight of oxide A and oxide B ratio of 9: 1 to 1: 9 Ru der. In this case, the ratio R = Wp / Wn is in the range of 1.3 to 2.2.
In another aspect of the present invention, the active material of the negative electrode, as a main component an alloy or a metal compound, lithium composite oxide, Ru mixture der between the oxide B and the oxide A or an oxide A,. In this case, the ratio R = Wp / Wn is Ri range near the 2.5 to 19, when the lithium composite oxide is an oxide A, the ratio R is in the range of 3.0 to 19. When the lithium composite oxide is a mixture of oxide B and the oxide A, the weight ratio between the oxide A and the oxide B is 9: 1 to 1: 9 Ru der.

  Even if the nonaqueous electrolyte secondary battery of the present invention is used by setting the end-of-charge voltage in a normal operating state to a range of 4.25 to 4.5 V, it maintains a high capacity and sufficient safety, and Operates normally.

  A nonaqueous electrolyte secondary battery according to the present invention includes a negative electrode including an active material capable of inserting and extracting lithium, a positive electrode including a lithium composite oxide as an active material, a separator separating the negative electrode and the positive electrode, and lithium ion conductivity The end-of-charge voltage is set to 4.25 to 4.5V.

The non-aqueous electrolyte secondary battery of the present invention maintains sufficient safety and operates normally even if it is used with the end-of-charge voltage in the normal operating state set in the range of 4.25 to 4.5V. .
Here, the normal operating state refers to a state in which the nonaqueous electrolyte secondary battery operates normally, and is also an operating state recommended by the battery manufacturer.
The charge end voltage is a reference voltage for stopping the constant current charging of the battery. When the battery being charged reaches the reference voltage, the constant current charging of the battery is stopped. Usually, constant voltage charging is performed thereafter with this reference voltage. The constant voltage charging is stopped when the predetermined time is reached or when the current becomes equal to or lower than the predetermined current value. The end-of-charge voltage is determined in advance according to the design of the nonaqueous electrolyte secondary battery.
The end-of-charge voltage in the normal operating state is generally an upper limit voltage in a battery voltage range that is suitable or recommended for normal operation of the nonaqueous electrolyte secondary battery.

  The nonaqueous electrolyte secondary battery according to the present invention includes a weight Wp per unit area of the active material contained in the positive electrode and a weight Wn per unit area of the active material contained in the negative electrode in a region where the positive electrode and the negative electrode face each other. The ratio R = Wp / Wn (hereinafter simply referred to as the weight ratio R of the positive and negative electrode active materials) is in the range of 1.3 to 19. As a result, the positive and negative loads are balanced, and the capacity is high and the reliability is excellent. Here, the weight ratio R can be converted into a capacity ratio, but when actually manufacturing a battery, the active material is measured by weight to prepare an electrode mixture. It is clearer and clearer.

In a preferred embodiment of the present invention, the negative electrode active material is mainly composed of a carbonaceous material capable of inserting and extracting lithium, and the weight ratio R is in the range of 1.3 to 2.2, more preferably 1.7. It is in the range of ~ 2.0.
In another preferred embodiment of the present invention, the negative electrode active material is mainly composed of an alloy or metal compound capable of inserting and extracting lithium, and the weight ratio R is in the range of 2.5 to 19.
According to the above-described embodiment, even if the end-of-charge voltage in a normal operating state is set to 4.25 V or more, the battery functions such as cycle characteristics, heat resistance, storage characteristics as well as safety operate normally. A high-capacity nonaqueous electrolyte secondary battery can be obtained.

  Here, in a battery whose negative electrode active material is mainly a carbonaceous material capable of inserting and extracting lithium, when the weight ratio R is less than 1.3, or an alloy or metal compound in which the negative electrode active material can store and release lithium When the weight ratio R is smaller than 2.5, the weight of the negative electrode increases with respect to the positive electrode, and the thermal stability of the battery decreases when the battery is placed at a high temperature. Further, in a battery in which the negative electrode active material is mainly composed of the carbonaceous material, when the weight ratio R is larger than 2.2, or in the battery in which the negative electrode active material is mainly composed of the alloy or the metal compound, the weight ratio R is If it is larger than 19, the load on the negative electrode is too large relative to the load on the positive electrode, so that lithium metal may be deposited on the negative electrode after a cycle, and the reliability of the battery is lowered.

In a preferred embodiment of the present invention, the positive electrode active material is a lithium composite oxide represented by the following formula (1).
Li _x Co _{1- y My} O ₂ (1)
Where M is from the group consisting of Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba. At least one element selected, and 1.0 ≦ x ≦ 1.15 and 0.005 ≦ y ≦ 0.1.

  Here, when the negative electrode active material is mainly a carbonaceous material capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 1.5 to 2.2. When the negative electrode active material is mainly composed of an alloy or metal compound capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 3.0 to 19.

In another preferred embodiment of the present invention, the positive electrode active material is a lithium composite oxide represented by the following formula (2).
Li _x Ni _y Mn _z M _{1 -yz} O ₂ (2)
In the formula, M is at least one element selected from the group consisting of Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, and Re. 1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 0.5, 0.9 ≦ y / z ≦ 3.0.

  Here, when the negative electrode active material is mainly a carbonaceous material capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 1.3 to 2.0. When the negative electrode active material is mainly composed of an alloy or metal compound capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 2.5-18.

In still another preferred embodiment of the present invention, the positive electrode active material is a mixture of the oxide A represented by the formula (1) and the oxide B represented by the formula (2) at a predetermined ratio. A mixture.
Here, when the negative electrode active material is mainly composed of a carbonaceous material capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 1.3 to 2.2. When the negative electrode active material is mainly composed of an alloy or metal compound capable of inserting and extracting lithium, the weight ratio R of the positive and negative electrode active materials is preferably in the range of 2.5 to 19.

As the alloy or metal compound capable of inserting and extracting lithium, at least one selected from the group consisting of Si, Sn, Si or Sn, and SiO is preferable because a high capacity can be expected.
The mixing ratio of the positive electrode active material A and the positive electrode active material B is preferably 9: 1 to 1: 9 by weight. More preferably, it is 9: 1 to 5: 5. The electron conductivity of the positive electrode active material A and the high capacity of the positive electrode active material B exhibit complementary effects, and a battery with higher capacity and excellent discharge characteristics at low temperatures can be realized.

  The positive electrode active material of the present invention has Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Sn, Bi, It is preferable that at least one metal selected from the group consisting of Cu, Si, Ga, and B, an intermetallic compound containing the metal, or an oxide of the metal is coated. In a high voltage battery in which the end-of-charge voltage in a normal operating state is set to 4.25 to 4.5 V, there is an effect of suppressing metal elution from the positive electrode active material in a high-voltage charged state. This is because deterioration of the positive electrode active material accompanying the progress of the discharge cycle is suppressed, and the capacity retention rate is improved.

In still another preferred embodiment of the present invention, the positive electrode contains an oxide represented by the formula (3) in addition to any of the positive electrode active materials described above.
MO _x (3)
Wherein M is at least selected from the group consisting of Li, Co, Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, and Re. One element, 0.4 ≦ x ≦ 2.0.
According to this embodiment, there is an effect of suppressing metal elution from the positive electrode active material in a high-voltage charge state, and as a result, deterioration of the positive electrode active material accompanying the progress of the charge / discharge cycle is suppressed, and the capacity retention rate Is improved.

In still another preferred embodiment of the present invention, the nonaqueous electrolyte contains cyclic carbonates and acyclic carbonates as a solvent. Cyclic carbonates suppress the decomposition of the electrolyte by forming a good-quality film on the negative electrode surface. In addition, the acyclic carbonate reduces the viscosity of the electrolyte and promotes the penetration of the electrolyte into the electrode plate.
The ratio of the cyclic carbonates in the electrolyte is preferably 10 to 50% by volume ratio at 20 ° C. If it is less than 10%, the formation of a good quality film on the negative electrode surface is reduced, the reactivity between the negative electrode and the electrolyte is increased, and the decomposition of the electrolyte is promoted. If it is more than 50%, the viscosity of the electrolyte is increased and the penetration of the electrolyte into the electrode plate is prevented.

In another preferred embodiment of the present invention, the non-aqueous electrolyte contains LiPF ₆ as a lithium salt. In a more preferred embodiment, LiPF ₆ is contained in an amount of 0.5 to 2.0 mol / l, and further LiBF ₄ is contained in an amount of 0.01 to 0.3 mol / l. When the concentration of LiPF ₆ is smaller than 0.5 mol / l, decomposition of LiPF ₆ proceeds with the passage of the cycle, and normal discharge cannot be performed due to the lack of lithium salt. When the concentration of LiPF ₆ is larger than 2.0 mol / l, the viscosity of the electrolyte increases, and smooth electrolyte penetration into the electrode plate is hindered. LiBF ₄ suppresses the decomposition of the electrolyte during the cycle, and is effective in improving the cycle characteristics. When the concentration of LiBF ₄ is less than 0.01 mol / l, no sufficient effect of improving the cycle characteristics is observed, and when it is greater than 0.3 mol / l, the product of LiBF ₄ decomposition inhibits the migration of lithium ions. As a result, the discharge characteristics are degraded.

In still another preferred embodiment of the present invention, the non-aqueous electrolyte contains at least one benzene derivative containing a phenyl group and a group having a tertiary or quaternary carbon adjacent to the phenyl group as an additive. Contains. The additive has an effect of suppressing thermal runaway when the battery is overcharged.
The additive is preferably at least one selected from the group consisting of cyclohexylbenzene, biphenyl, and diphenyl ether. The content of the additive is preferably 0.05 to 8.0% by weight, more preferably 0.1 to 6.0% by weight, based on the whole nonaqueous electrolyte. When content of the said additive is smaller than the said range, the effect which suppresses the thermal runaway at the time of overcharge is not recognized. In addition, when the content of the additive is larger than the above range, the excessive additive prevents the movement of lithium ions and causes a decrease in discharge characteristics.

  The negative electrode active material used in the present invention is a carbonaceous material, alloy, and metal compound capable of inserting and extracting lithium, and conventionally known materials can be applied. Examples of the carbonaceous material include pyrolytic carbons; cokes such as pitch coke, needle coke, and petroleum coke; graphites, glassy carbons, and fired bodies of organic polymer compounds such as phenol resins and furan resins. A polymer obtained by calcining and carbonizing a polymer compound; carbon materials such as carbon fiber and activated carbon can be raised. The alloy is preferably at least one selected from the group consisting of Si, Sn, Al, Zn, Mg, Ti, and Ni. Examples of the metal compound include at least one selected from the group consisting of the metal oxide and carbide. More preferable is at least one selected from the group consisting of Si, Sn, Si or Sn-containing alloys, and SiO. These materials can be used alone or in admixture of two or more. The average particle diameter of these negative electrode active materials is not particularly limited, but is preferably 1 to 30 μm.

As the negative electrode binder, a thermoplastic resin, a thermosetting resin, or the like is used. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer Polymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer Polymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetra Ruoroechiren copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its (Na ⁺⁾ ion crosslinked body, an ethylene - methacrylic acid copolymer or its (Na ⁺ And ionic cross-linked product, ethylene-methyl acrylate copolymer or its (Na ⁺ ) ionic cross-linked product, ethylene-methyl methacrylate copolymer or its (Na ⁺ ) ionic cross-linked product. These materials can be used alone or as a mixture. Among these materials, styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid copolymer or its (Na ⁺ ) ion crosslinked product. An ethylene-methyl acrylate copolymer or its (Na ⁺ ) ion crosslinked product, and an ethylene-methyl methacrylate copolymer or its (Na ⁺ ) ion crosslinked product are particularly preferred.

  The conductive material for the negative electrode may be anything as long as it is an electron conductive material. For example, natural graphite such as flaky 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, etc. These include conductive powders such as: metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives, and these can be used alone or in combination. Among these conductive materials, artificial graphite, acetylene black, and carbon fiber are particularly preferable. The addition amount of the conductive material is not particularly limited, but is preferably 1 to 30 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  The current collector for the negative electrode may be an electron conductor that is substantially chemically stable in the constructed battery. For example, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, and the like as materials, composite materials obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium are also included. Of these, copper and copper alloys are particularly preferable. You may oxidize and use the surface of these materials. Moreover, it is preferable to give an unevenness | corrugation to the collector surface by surface treatment. As the shape, a foil, a film, a sheet, a net, a punched one, a lath body, a porous body, a foam, a molded body of a fiber group, or the like is used. The thickness is not particularly limited, but is preferably 1 to 500 μm.

The lithium ion conductive nonaqueous electrolyte is composed of a solvent, a lithium salt dissolved in the solvent, and an additive added as necessary. Known materials can be used as the non-aqueous solvent. Among them, a mixed system of cyclic carbonates such as ethylene carbonate and propylene carbonate and acyclic carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and dibutyl carbonate is preferable. It is preferably 10 to 50% of the whole solvent. The lithium salt is not particularly limited in the present invention, and LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂₎ that are usually used in non-aqueous electrolyte secondary batteries. ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiB [C ₆ F ₃ (CF ₃ ) ₂ ] _{4 and the} like can be used. Of these, LiPF ₆ is preferably used in the range of 0.5 to 2.0 mol / l, and LiPF ₆ and LiBF ₄ are preferably used in amounts of 0.5 to 2.0 mol / l and 0.01 to 0.3 mol / l, respectively. It is preferable to use in the range. As described above, the nonaqueous electrolyte used in the present invention is not particularly limited, and any of those commonly used in nonaqueous electrolyte secondary batteries can be used. Two or more of these electrolytes can be mixed and used. Examples of additives include known cyclic carbonates having an unsaturated bond such as vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, and the like, tertiary groups adjacent to phenyl groups such as cyclohexylbenzene, biphenyl, and diphenyl ether, and the phenyl groups. One or more sulfur-containing organic compounds such as benzene derivatives and propane sultone containing a group having a quaternary carbon can be used. The proportion of these additives is preferably 0.05 to 8.0%, more preferably 0.1 to 6.0% of the whole nonaqueous electrolyte in terms of weight ratio.

  As the separator used in the present invention, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, it is preferable to have a function of closing the hole at a certain temperature or higher and increasing the resistance. The pore diameter of the separator is desirably in a range in which the positive / negative electrode material, the binder, and the conductive agent detached from the electrode do not permeate, and is preferably 0.01 to 1 μm, for example. A separator having a thickness of 10 to 300 μm can be used. The porosity is determined according to the permeability of the electrons and ions, the material, and the film pressure, but is generally preferably 30 to 80%. Moreover, what absorbed and hold | maintained the organic electrolyte comprised from a solvent and lithium salt melt | dissolved in the solvent to a polymer material can be used as a separator. The polymer material holding the organic electrolyte may be included in the positive electrode mixture or the negative electrode mixture, and further integrated with the positive electrode and / or the negative electrode. The polymer material may be any material that can absorb and retain an organic electrolyte, but polyvinylidene fluoride is particularly preferable.

The positive electrode active material used in the present invention is a lithium composite oxide, and in particular, a material in which a part of the constituent metal element is substituted with a third or fourth metal element (hereinafter referred to as a different metal element) is preferable. . In a lithium composite oxide to which a different metal element is not added, for example, lithium cobalt oxide, in a charged state where the battery voltage is changed from around 4.2 V (the positive electrode potential is around 4.25 V to the metal Li) to 4.45 V, Phase transition from hexagonal to monoclinic. When the battery is further charged, the composite oxide undergoes a phase transition to the hexagonal system, and a monoclinic system appears again from around 4.6V. These monoclinic crystal structures appear when the entire crystal is distorted. Therefore, in the monoclinic complex oxide, the binding force between the oxygen ions that play a central role in maintaining the crystal structure and the metal ions present in the surrounding area decreases, and the heat resistance of the complex oxide is reduced. It is known to decrease significantly.
Therefore, in the present invention, the stability of the crystal is increased by adding a small amount of a different metal to the lithium composite oxide so that the battery is set to operate normally even at a high voltage.

In a preferred embodiment of the present invention, the lithium composite oxide to which a different metal is added is an oxide represented by the formula (1). In the formula, the value of x varies depending on the charge / discharge of the battery.
The composition of the oxide just after synthesis is preferably 1.0 ≦ x ≦ 1.15 in the above formula. If x is 1.0 or more, the effect of suppressing the occurrence of lithium deficiency can be obtained. In order to further improve the structural stability of the oxide as an active material, x is particularly preferably 1.01 or more.
On the other hand, when x is less than 1, the lithium necessary for the synthesis of the high-performance active material is insufficient. That is, the content rate of by-products such as Co ₃ O ₄ contained in the active material is increased, and gas generation and capacity reduction due to Co ₃ O ₄ occur inside the battery.

  M in the above formula is an element necessary for crystal stability as described above. Among the elements raised to the formula (1), it is particularly preferable to use at least one selected from the group consisting of Mg, Al, Ti, Mn, Ni, Zr, Mo, and W. The surface of the active material is stabilized by being covered with the above-described particularly preferable oxide of element M or a composite oxide of lithium and M, and even at a high potential, the decomposition reaction of the non-aqueous electrolyte and the crystal of the positive electrode active material Destruction is suppressed. In order to obtain the effect of stabilizing the element M, it is necessary to satisfy at least 0.005 ≦ y. However, when 0.1 <y, a decrease in capacity of the active material becomes a problem.

Among the positive electrode active materials described above, the formula Li _x Co _1-yz Mg _y Al _z O ₂ (1.0 ≦ x ≦ 1.02, 0.005 ≦ y ≦ 0.1, 0.001 ≦ z <0) .05) is preferably used. The positive electrode using this oxide has almost the same thermal stability as 4.2 V even when the potential is 4.8 V with respect to lithium.

Although the detailed mechanism is not clear, it is considered as follows.
That is, by replacing a part of Co with a suitable amount of Mg, the stability of the crystal when Li is released by charging is increased, and oxygen desorption is not observed. In another aspect, the oxide has a high electronic conductivity, and as a result of the effect as a certain conductive material, a uniform potential distribution is formed in the positive electrode, resulting in a locally higher voltage state than the surroundings. It is thought that Co which becomes becomes relatively decreased, and as a result, a decrease in thermal stability is suppressed.
Here, when x is less than 1, an oxide of a metal such as Co is easily generated as an impurity, and there is a disadvantage that gas is generated during the charge / discharge cycle. Moreover, when y which is the amount of substitution of Mg is less than 0.005, the above effect cannot be exhibited, and when it exceeds 0.1, the capacity is reduced.

  On the other hand, Al has the effect of further strengthening the action of Mg for improving heat resistance by stabilizing the structure, although the reason is not clear. However, the substitution amount of Al is preferably small, and when it is 0.05 or more, the capacity is reduced. However, if it is 0.001 or more, there is an effect of the present invention.

In another preferred embodiment of the present invention, the lithium composite oxide to which a different metal is added is an oxide represented by the formula (2). The value of x varies depending on the charge / discharge of the battery.
The composition of the oxide immediately after synthesis is preferably 1.0 ≦ x ≦ 1.15. If x is 1.0 or more, the effect of suppressing the occurrence of lithium deficiency can be obtained. In order to further improve the structural stability of the oxide as an active material, x is particularly preferably 1.01 or more. On the other hand, when x is less than 1, the lithium necessary for the synthesis of the high-performance active material is insufficient. That is, the content rate of by-products contained in the active material increases, and gas generation and capacity reduction occur inside the battery.
Y indicating Ni content and z indicating Mn content are 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 0.5, and 0.9 ≦ y / z ≦ 3.0. The addition of the element M makes it stable even at a high voltage.
The lithium composite oxide represented by the formulas (1) and (2), which are positive electrode active materials used in the present invention, are mixed in a oxidizing atmosphere with raw material compounds corresponding to the composition ratio of each metal element. And obtained by firing. As the raw material compound, oxides, hydroxides, oxyhydroxides, carbonates, nitrates, organic complex salts, and the like of each metal element constituting the composite oxide can be used alone or in admixture of two or more. In order to facilitate the synthesis of the lithium composite oxide, it is preferable to use solid solutions such as oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and organic complex salts of each metal element.

  Since the oxidizing atmosphere and the firing temperature at the time of synthesizing the lithium composite oxide depend on the composition, the synthesis amount, and the synthesis apparatus, it is preferable to determine these in consideration. Ideally, this lithium composite oxide should have a single phase, but a multiphase mixture containing a small amount of other phases obtained in industrial mass production may be used as the lithium composite oxide. Further, elements other than those described above may be mixed as impurities as long as they are within the range of amounts normally contained in industrial raw materials. The average particle diameter of the positive electrode active material is not particularly limited, but is preferably 1 to 30 μm.

  The conductive material for the positive electrode may be any electron conductive material that is substantially chemically stable in the constructed battery. For example, natural graphite such as flake graphite, graphite such as artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductivity such as carbon fiber and metal fiber Fibers; carbon fluoride; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and organic conductive materials such as polyphenylene derivatives . These can be used alone or as a mixture. Among these conductive materials, artificial graphite and acetylene black are particularly preferable. The addition amount of the conductive material is not particularly limited, but is preferably 1 to 50 parts by weight, and more preferably 1 to 30 parts by weight with respect to 100 parts by weight of the positive electrode active material. In the case of carbon or graphite, 1 to 15 parts by weight is particularly preferable.

As the positive electrode binder, a thermoplastic resin, a thermosetting resin, or the like is used. For example, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer Polymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), fluoride Vinylidene-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-he Sa hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its (Na ⁺⁾ ion crosslinked body, an ethylene - methacrylic acid copolymerization Or a (Na ⁺ ) ion crosslinked product thereof, an ethylene-methyl acrylate copolymer or its (Na ⁺ ) ion crosslinked product, an ethylene-methyl methacrylate copolymer or its (Na ⁺ ) ion crosslinked product, etc. These materials can be used alone or as a mixture. Of these materials, polyvinylidene fluoride and polytetrafluoroethylene are particularly preferable.

The current collector for the positive electrode may be an electron conductor that is substantially chemically stable in the constituted battery. For example, in addition to aluminum, stainless steel, nickel, titanium, carbon, conductive resin, and the like as materials, a composite material obtained by coating the surface of aluminum or stainless steel with carbon or titanium can also be used. Of these, aluminum and aluminum alloys are particularly preferable. You may oxidize and use the surface of these materials. Moreover, it is preferable to give an unevenness | corrugation to the collector surface by surface treatment.
As the shape of the positive electrode current collector, a foil, a film, a sheet, a net, a punched one, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like is used. The thickness is not particularly limited, but is preferably 1 to 500 μm.

  In addition to the conductive material and the binder, a filler, a dispersant, an ionic conductor, a pressure enhancer, and other various additives may be added to the positive electrode mixture and the negative electrode mixture, respectively. As a filler, what is necessary is just a chemically stable fibrous material in the comprised battery. Usually, olefin polymers such as polypropylene and polyethylene, glass fibers, and carbon fibers are used. Although the addition amount of a filler is not specifically limited, 0-10 weight part is preferable with respect to 100 weight part of positive mix and negative mix, respectively.

The non-aqueous electrolyte secondary battery of the present invention is used as a power source for devices such as mobile phones and personal computers in combination with a charge control device that controls the charge end voltage to a voltage set in the range of 4.25 to 4.5V. Used.
FIG. 2 is a block diagram showing the configuration of such a charging control apparatus. The control device shown here also includes a discharge control device.
Reference numeral 10 denotes a nonaqueous electrolyte secondary battery according to the present invention. A current detection unit 11 is connected in series with the battery 10. A voltage detector 12 is connected in parallel with the series circuit of the battery 10 and the current detector 11. 16a and 16b are input terminals for charging the battery 10, and 17a and 17b are output terminals connected to the device. A changeover switch 15 is provided in series with the battery 10. The switch 15 is switched to the charge control unit 13 side during charging and to the discharge control unit 14 side during discharging.
Examples of the present invention will be described below.

Reference example 1
(Production of battery)
FIG. 1 shows a rectangular nonaqueous electrolyte secondary battery having a thickness of 5.2 mm, a width of 34 mm, and a height of 50 mm used in the reference examples and examples. The electrode plate group 1 is constituted by winding a belt-like positive electrode plate, a negative electrode plate, and a separator inserted between them in a spiral shape. The positive and negative electrode plates, their respective aluminum positive electrode lead 2 and a nickel negative electrode lead 3 is welded. The electrode plate group 1 is housed in an aluminum battery case 4 with a polyethylene resin insulating ring attached to the top thereof. The end of the positive electrode lead 2 is spot welded to the aluminum sealing plate 5. Further, the end portion of the negative electrode lead 3 is spot welded to the lower portion of the nickel negative electrode terminal 6 attached to the central portion of the sealing plate 5 via the insulating gasket 7. It is joined hermetically and liquid-tight by laser over welding the opening and the sealing plate 5 of the battery case 4. A predetermined amount of the non-aqueous electrolyte is injected from the liquid injection port of the sealing plate, and then the liquid injection port is sealed by laser welding an aluminum plug 8.

The positive electrode was produced as follows.
First, LiCo _0.94 Mg _0.05 Al _0.01 O ₂ was used as the positive electrode active material. To 100 parts by weight of this positive electrode active material, 3 parts by weight of acetylene black as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder are mixed with an N-methylpyrrolidinone solution of polyvinylidene fluoride. The mixture was stirred to obtain a paste-like positive electrode mixture. Next, the paste-like positive electrode mixture was applied to both sides of an aluminum foil current collector with a thickness of 20 μm, dried, rolled with a rolling roller, and cut into a predetermined size to obtain a positive electrode plate. The amount of the active material contained in the positive electrode plate was 22.8 mg / cm ² per unit area on one side of the current collector.

The negative electrode was produced as follows.
First, flaky graphite ground and classified so as to have an average particle size of about 20 μm and 3 parts by weight of styrene-butadiene rubber as a binder are mixed, and then carboxymethyl cellulose is 1% by weight with respect to graphite. Thus, an aqueous carboxymethyl cellulose solution was added and mixed by stirring to obtain a paste-like negative electrode mixture. The paste-like negative electrode mixture was applied to both sides of a 15 μm thick copper foil current collector, dried, rolled with a rolling roller, and cut into a predetermined size to obtain a negative electrode plate. The amount of the active material contained in the negative electrode plate was 11.4 mg / cm ² per unit area of one surface of the current collector facing the positive electrode.

In general, the negative electrode plate has a larger area than the positive electrode plate and is opposed to the positive electrode. The negative electrode active material that does not face the positive electrode does not participate in the charge / discharge reaction. In the present invention, the amount of the positive electrode active material and the negative electrode active material per unit area of one side of the current collector is defined in the portion that is not involved in such charge / discharge but in the portion that is involved in charge / discharge facing the counter electrode. Is.
Next, a strip-shaped positive electrode plate and negative electrode plate produced as described above, and a microporous polyethylene resin separator having a thickness of 25 μm inserted between the two electrodes were spirally wound. The weight ratio R of the positive and negative electrode active materials was 2.0.

As the non-aqueous electrolyte, a solution obtained by dissolving 1.0 mol / l of LiPF ₆ in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 30:70 at 20 ° C. was used.
After the rolled electrode plate group was inserted into the battery case, an electrolyte solution was injected and sealed. The battery fabricated in this manner was batteries 6.

Further, batteries 1 to 5 and 7 to 9 were produced in the same manner as the battery 6 except that the weight ratio R was changed as shown in Table 1 by changing the weight of the positive and negative active materials.
For comparison, a comparative battery A was prepared in the same manner as the battery 6 except that only LiCoO ₂ was used as the positive electrode active material.

(Battery evaluation)
The batteries 1 to 9 produced as described above and the battery A of the comparative example were subjected to 500 charge / discharge cycles at an environmental temperature of 20 ° C. Charging was performed at a constant current of 4.25 V, 4.4 V, or 4.5 V for 2 hours with a maximum current of 600 mA. Discharging was performed at a constant current of 600 mA until the voltage dropped to 3.0V. The discharge capacity after the elapse of 500 cycles was measured and evaluated by the ratio to the initial capacity (capacity at the second cycle).

In addition, after confirming the initial capacity, the battery was charged at a constant voltage of 4.2 V, 4.25 V, 4.4 V, or 4.5 V for 2 hours, and then the battery was increased at 5 ° C./min in the temperature bath. The limit temperature (indicated as thermal runaway limit temperature) leading to thermal runaway was measured.
Table 1 shows the weight ratio R of the positive and negative electrode active materials of the battery obtained above, and Table 2 shows the capacity retention rate after 500 cycles and the thermal runaway limit temperature in the heating temperature rise test, and the set end-of-charge voltage. Shown for each.

As can be seen from Table _{2, LiCo 0.94 Mg 0.05 Al 0.01} O 2 batteries 1-9 was used as the positive electrode active material, as compared to cell A of the comparative example using LiCoO ₂ as the positive electrode active material, cycle characteristics It is good and has a high capacity retention rate even when the charging voltage is high.

As a result of disassembling the deteriorated battery and conducting X-ray diffraction analysis of the positive electrode, in the battery of the comparative example, the crystal structure of the positive electrode active material was changed at the end of the cycle, and charging and discharging were repeated at a high voltage. It was found that the positive electrode active material was significantly deteriorated.
On the other hand, in the batteries using _{LiCo 0.94 Mg 0.05 Al 0.01 O 2} , after a lapse of 500 cycles, as a result of the X-ray diffraction analysis of the positive electrode, the crystal structure of the positive electrode active material maintains the initial structure It was confirmed that the crystal structure was stable even when charging and discharging were repeated at a high voltage.

  In addition, the batteries 1 to 7 having the positive / negative active material weight ratio R in the range of 2.2 or less have the cycle characteristics of the active material weight ratio R of the batteries 8 and 9 of 2 when the charging voltage is increased. It was even better than batteries larger than .2. Similarly, the batteries 8 and 9 were analyzed by X-ray diffraction. As a result, the crystal structure of the positive electrode active material was not changed, and no deterioration of the positive electrode was observed. However, since the weight ratio R between the positive and negative electrode active materials is 2.3 or more and the weight of the negative electrode is small, the load on the negative electrode during charging is large, the negative electrode potential is always low, and reductive decomposition products of the electrolyte accumulate. It became clear that the charge / discharge reaction was hindered. For this reason, the movement resistance of lithium ions is increased, and it is presumed that the capacity decreased as the cycle was repeated.

From the above results, it was found that the batteries 1 to 9 showed high cycle characteristics even in the use region where the charge / discharge voltage was as high as 4.25 V to 4.5 V. In particular, it was found that good cycle characteristics can be obtained in a battery having a positive / negative active material weight ratio R smaller than 2.2.

Next, the safety of a battery charged to a high voltage will be described.
As can be seen from Table 2, in the comparative battery using LiCoO ₂ as the positive electrode active material, the thermal runaway limit temperature is as high as 160 ° C. at a charging voltage of 4.2 V, but the charging voltage is increased. It can be seen that the thermal runaway limit temperature is remarkably lowered and the safety as a battery is lowered. In the battery 1-9 using Shi pairs to _{L iCo 0.94 Mg 0.05 Al 0.01 O} 2 as the positive electrode active material, the thermal runaway limit temperature charging voltage with very high and 4.5V is maintained at least 0.99 ° C. It was confirmed that the safety was extremely high and the effect of adding Mg and Al to the positive electrode active material clearly appeared.

Further, the batteries 4 to 7 having the positive / negative active material weight ratio R in the range of 1.5 to 2.2 have a thermal runaway limit temperature of 170 ° C. even when the charging voltage is increased to 4.5V. As described above, it was found to be more stable and preferable.
In batteries with a positive / negative active material weight ratio R of 1.4 or less, the negative electrode active material ratio is extremely large compared to the positive electrode, so the heat generated by the decomposition reaction between the negative electrode and the electrolyte controls the overall safety of the cell. Therefore, it is considered that the safety is slightly lowered. In particular, a battery having a weight ratio R of 1.2 was not good.

From the above results, it was found that the batteries 1 to 9 show high safety even in the use region where the charge / discharge voltage is as high as 4.25V to 4.5V. In particular, it has been found that a battery having a weight ratio R in an opposing unit area of greater than 1.5 can provide higher safety.

Considering the above two test results comprehensively, by setting the weight ratio R of the positive and negative electrode active materials in the range of 1.3 to 2.2, a battery with higher capacity can be realized. In particular, it was found that batteries having a weight ratio R in the range of 1.5 to 2.2 are preferable because they have excellent cycle characteristics and safety even when the charging voltage is as high as 4.25 to 4.5 V.
Similar results were obtained when the additive element M was an element other than Mg and Al, for example, Ti, Mn, Ni, Zr, Mo, and W.

Reference example 2
Batteries 10 to 18 were produced in the same manner as in Reference Example 1 except that LiNi _0.4 Mn _0.4 Co _0.2 O ₂ was used as the positive electrode active material, and the same evaluation as in Reference Example 1 was performed. Table 3 shows the weight ratio R of the positive and negative electrode active materials.
Table 4 shows the capacity retention rate after 500 cycles and the thermal runaway limit temperature in the heating temperature rise test for each set end-of-charge voltage.

In the same manner as in Reference Example 1, batteries 11 to 16 exhibited excellent cycle characteristics and safety. In particular, the batteries 11 to 15 having the positive / negative active material weight ratio R in the range of 1.3 to 2.0 have cycle characteristics and safety even when the charging voltage is as high as 4.25 to 4.5V. It was found that the properties were excellent and particularly preferable.
Similar results were obtained with Mg, Al, Ti, Zr, Mo, and W, where the additive element M is an element other than Co.

Example 1
Table 5 shows the results obtained in the same manner as in Reference Example 1 except that a mixture of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.4 Mn _0.4 Co _0.2 O ₂ in a weight ratio of 70:30 was used as the positive electrode active material. Batteries 19 to 27 having the weight ratio R of the positive and negative electrode active materials shown were produced and evaluated in the same manner as in Reference Example 1.
Table 6 shows the capacity retention rate after 500 cycles and the thermal runaway limit temperature in the heating temperature rise test for each set end-of-charge voltage.

The batteries 20 to 25 of the present invention exhibited excellent cycle characteristics and safety, and it was found that the cycle characteristics and safety were excellent even when the charging voltage was as high as 4.25 to 4.5 V. Also, overall, the cycle characteristics at a high voltage were superior to those of Reference Example 1.

Example 2
Other than mixing LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.4 Mn _0.4 Co _0.2 O ₂ as the positive electrode active material at the weight ratio shown in Table 7, and setting the weight ratio R of the positive and negative electrode active materials to 2.0. Produced the batteries 28 to 37 in the same manner as in Reference Example 1, and evaluated the discharge capacity and the low-temperature discharge characteristics. The discharge capacity is a maximum current of 600 mA at an environmental temperature of 20 ° C., and a constant voltage charge of 4.25 V, 4.4 V, or 4.5 V is performed for 2 hours, and the voltage drops to 3.0 V at a current of 600 mA. Each of the discharge capacities was measured. These discharge capacities were expressed as a ratio relative to the discharge capacity after charging at 4.25 V of the battery 28 as 100. The low-temperature discharge characteristics were expressed as the ratio of the discharge capacity at −10 ° C. to the discharge capacity at 20 ° C. by charging and discharging under the same conditions as described above at ambient temperatures of 20 ° C. and −10 ° C.
Table 8 shows the ratio of the discharge capacity and the ratio of the low-temperature discharge capacity of each battery for each set charge end voltage.

In the mixed active material of the positive electrode, the higher the ratio of LiNi _0.4 Mn _0.4 Co _0.2 O ₂ , the higher the discharge capacity ratio. In particular, at high voltages of 4.4 V and 4.5 V, LiNi _0.4 Mn _0.4 Co _0.2 O ₂ The increase in discharge capacity is large in the batteries 29 to 37 and the battery 24 in which the ratio is in the range of 10% by weight or more. There are two possible causes for this. The first is that LiNi _0.4 Mn _0.4 Co _0.2 O ₂ has a larger capacity per unit weight. Second, by mixing LiCo _0.94 Mg _0.05 Al _0.01 O ₂ with a relatively small irreversible capacity and LiNi _0.4 Mn _0.4 Co _0.2 O ₂ with a relatively large irreversible capacity, the irreversible capacity difference between the positive and negative electrodes is small. That is.

In the batteries 28 to 36 and the battery 24 in which the weight ratio of the two types of positive electrode active materials was 95/5 to 10/90, improvement in low-temperature discharge characteristics was observed. Further, at high voltages of 4.40 V and 4.50 V, excellent low temperature characteristics were observed in the batteries 28 to 32 and the battery 24 in which the weight ratio of the positive electrode active material was 95/5 to 50/50. This is considered to be because the electronic conductivity of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ is excellent.
From the above results, LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.4 Mn _0.4 Co _0.2 O ₂ were mixed in a weight ratio range of 90/10 to 10/90, preferably in the range of 90/10 to 50/50. Thus, it has been clarified that a battery having a higher capacity and excellent low-temperature discharge characteristics can be realized.

Reference example 3
A battery 38 was produced in the same manner as the battery 6 of Reference Example 1, except that 1.0 part by weight of cyclohexylbenzene was added to 100 parts by weight of the electrolyte. The battery 38 was subjected to an overcharge test together with the battery 6. In the overcharge test, 10 cells in a discharged state were prepared, charged continuously for 5 hours at a maximum current of 600 mA, and the number of cells leading to thermal runaway was compared.
As a result, three of the batteries 6 out of 10 cells had a thermal runaway, but all 10 cells of the battery 38 did not have a thermal runaway. It has been found that cyclohexylbenzene, which has been reported to have an effect on an overcharge test in a battery designed based on the conventional 4.2V standard, exhibits an effect on overcharge even in a battery designed at a higher voltage. In addition, the same results as in the battery 38 were obtained with biphenyl and diphenyl ether.

Reference example 4
Batteries 39 to 50 were produced in the same manner as the battery 6 of Reference Example 1 except that an electrolyte in which LiPF ₆ and LiBF ₄ were dissolved at concentrations shown in Table 9 was used as the electrolyte, and the cycle characteristics were evaluated.
Table 9 shows the capacity retention rate after 500 cycles for each set charge end voltage.

The batteries 40 to 43 having a LiPF ₆ concentration of 0.5 to 2.0 mol / l showed excellent cycle characteristics similar to those of the battery 6, but the battery 39 having a concentration of 0.4 mol / l had a cycle retention rate. A decrease was observed. This is considered to be because the decomposition of LiPF ₆ progressed as the cycle progressed, and normal discharge could not be performed due to the lack of lithium salt after 500 cycles. A decrease was also observed in the battery 44 having a concentration of 2.1 mol / l, but this was because the viscosity of the electrolyte increased due to the concentration being too high, preventing smooth electrolyte penetration into the electrode plate. It is thought that.
On the other hand, in the batteries 46 to 49 using LiPF ₆ and LiBF ₄ in combination, further improvement in cycle characteristics was observed. Although this mechanism of action is not yet clear, it is thought that LiBF ₄ has an action of suppressing the decomposition of the electrolyte during the cycle. However, in the battery 45 having a LiBF ₄ concentration of 0.005 mol / l, the effect of LiBF ₄ was not observed, and in the battery 50 having a concentration of 0.4 mol / l, a decrease in cycle characteristics was observed.

From these results, it is possible to obtain good cycle characteristics when the concentration of LiPF ₆ is 0.5 to 2.0 mol / l, and further by adding LiBF ₄ to 0.01 to 0.3 mol / l, further cycle characteristics can be obtained. It became clear that improved.

Reference Example 5
Batteries 51 to 59 were produced in the same manner as the battery 6 of Reference Example 1 except that the electrolyte prepared in Table 10 was used as the solvent, and the same evaluation as in Reference Example 1 was performed.
Table 11 shows the capacity retention rate after 500 cycles and the thermal runaway limit temperature in the heating temperature rise test for each set charge end voltage.

  The battery 51 using a 30/70 volume mixing ratio of ethylene carbonate (EC) / diethyl carbonate (DEC) as a solvent shows a good result that the thermal runaway limit temperature is low, although a slight decrease in cycle characteristics is observed. Indicated. The battery 52 using the EC / dimethyl carbonate (DMC) volume mixing ratio of 30/70 had the same excellent results as the battery 6. Further, the battery 53 using a volume mixing ratio of EC / ethyl methyl carbonate (EMC) / DEC of 30/40/30 maintains excellent cycle characteristics equivalent to the battery 6 and has excellent thermal runaway equivalent to the battery 51. The limit temperature was indicated. Therefore, it became clear that more excellent characteristics can be obtained by using EMC and DEC together. Moreover, in the electrolyte containing EC, EMC, and DEC, EC is a volume ratio of 10-50% with respect to the whole solvent, EMC is a volume ratio of 20-60%, and DEC is a volume ratio of 10-50%. In this case, excellent cycle characteristics similar to those of the battery 53 and an excellent thermal runaway limit temperature were obtained.

  Further, the batteries 55 to 58 having an EC volume ratio of 10 to 50% showed excellent characteristics equivalent to the battery 6, but the battery 54 having a small EC ratio showed a decrease in both cycle characteristics and thermal runaway limit temperature. In addition, in the battery 59 having a large EC ratio, a decrease in cycle characteristics was observed. This is because when the EC ratio is small, a part of the EC is decomposed and the amount of a good quality film formed on the negative electrode is reduced, and the reactivity between the negative electrode and the electrolyte is increased. This is probably because the amount of heat generated by the reaction between the negative electrode and the electrolyte in the temperature rise test increased. On the other hand, when the EC ratio is large, the viscosity of the electrolyte increases, which is considered to be a result of hindering smooth electrolyte penetration into the electrode plate.

Reference Example 6
Batteries 60 to 79 were produced in the same manner as the battery 6 of Reference Example 1 except that LiCo _0.94 Mg _0.05 Al _0.01 O ₂ whose surface was coated with the material shown in Table 12 was used as the positive electrode active material. Evaluated.
The coating of the material on the active material surface was performed by mixing 3 parts by weight of each coating material having an average particle size of 10 μm with 100 parts by weight of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ , and stirring by ball mill in an Ar atmosphere. Implemented by doing time.
Table 12 shows the capacity maintenance rate after 500 cycles for each set charge end voltage.

  In the batteries 60 to 79 using the positive electrode active material whose surface was coated with each material, an improvement in the cycle retention rate was recognized as compared with the battery 6 using the active material not covered with such a material. By covering each material, the elution of the metal from the positive electrode active material in a high voltage charged state is suppressed, and as a result, the deterioration of the positive electrode active material with the progress of the cycle is suppressed, and the cycle maintenance rate is improved. It is thought that it was because it was done.

Reference Example 7
Batteries 80 to 87 were prepared in the same manner as the battery 6 of Reference Example 1 except that a positive electrode plate was prepared by mixing the metal oxides shown in Table 13 in addition to LiCo _0.94 Mg _0.05 Al _0.01 O ₂ as the positive electrode active material. And the cycle characteristics were evaluated. In these metal oxides, 1 part by weight of each material was mixed with 100 parts by weight of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ during the stirring and mixing of the positive electrode mixture.
Table 13 shows the capacity retention rate after 500 cycles for each set charge end voltage.

  In the batteries 80 to 87 in which various metal oxides were mixed with the positive electrode, an improvement in the cycle retention rate was recognized as compared with the battery 6 using the positive electrode plate in which these metal oxides were not mixed. This is because by including each oxide in the positive electrode plate, the elution of the metal from the positive electrode active material in a high-voltage charge state is suppressed, and as a result, the deterioration of the positive electrode active material with the progress of the cycle is suppressed, and the capacity is maintained. This is probably because the rate was improved.

Example 3
A negative electrode active material having a mean particle size of 5 μm mixed with SiO and scaly graphite at a weight ratio of 90:10, except that the weight ratio R of the positive and negative electrode active materials shown in Table 14 was used. A battery 88 was produced in the same manner as the battery 6 of Reference Example 1. A battery B of Comparative Example was fabricated in the same manner as Battery A of Comparative Example 1 of Reference Example 1 except that the same negative electrode active material as that of Battery 88 was used and the weight ratio R shown in Table 14 was used. For the battery 88 and the batteries A and B of the comparative examples, the discharge capacity density ratio, the discharge average voltage, and the cycle characteristics were evaluated.

Each battery is charged at a constant current of 4.20 V, 4.25 V, 4.4 V, or 4.5 V for 2 hours at an environmental temperature of 20 ° C. with a maximum current of 600 mA, and a voltage of 3.0 V at a constant current of 600 mA. The discharge capacity was measured by discharging until the voltage decreased. The ratio of the discharge capacity density is the ratio where the discharge capacity is converted into the discharge capacity per unit weight of the total weight of the positive and negative electrode active materials, and the discharge capacity density at 4.2 V of the battery A of Comparative Example is 100. expressed. The discharge average voltage was charged and discharged under the above conditions at an environmental temperature of 20 ° C., and the average voltage during discharge was measured.
Table 15 shows the discharge capacity density ratio and the discharge average voltage at each set voltage, and Table 16 shows the capacity maintenance rate after 500 cycles for each set charge end voltage.

  From Table 14, the battery 88 using a mixture of SiO and scaly graphite at a weight ratio of 90:10 as the negative electrode active material and the battery B of the comparative example were compared using scaly graphite as the negative electrode active material. Compared to the battery A of the example, the discharge capacity per active material weight is improved for both the positive and negative electrodes. Therefore, it can be seen that a high-capacity battery can be realized by using a metal compound or a negative electrode active material mainly composed of a metal compound. Further, by setting the voltage to 4.4V or 4.5V, the capacity can be further increased. However, as is clear from Table 15, the average discharge voltage of the battery using the metal compound or the negative electrode active material mainly composed of the metal compound is higher than that of the conventional battery using the negative electrode active material mainly composed of the carbonaceous material. Has the disadvantage of lowering. As a result, when a battery using a metal compound or a negative electrode active material mainly composed of a metal compound is incorporated in a conventional device having a charge end voltage of 4.2 V, the voltage drop of the battery is large when a large current flows. Therefore, there is a problem that the discharge capacity as designed cannot be taken out.

According to the present invention, by using a battery using a metal compound or a negative electrode active material mainly composed of a metal compound at a high voltage of 4.4 V or 4.5 V, an average discharge voltage can be reduced with a conventional carbonaceous material. The voltage can be increased to 3.6 to 3.7 V, which is equivalent to a battery using a negative electrode active material as a main component. Further, when this battery is incorporated in a device, even when a large current flows, the device is prevented from being stopped due to a voltage drop, and a discharge capacity as designed can be taken out.
Further, as apparent from Table 16, when a metal compound or a metal compound is mainly used as the negative electrode active material, the battery B of the comparative example using LiCoO ₂ as the positive electrode active material has a capacity retention rate after 500 cycles. On the other hand, the battery 88 using LiCo _0.94 Mg _0.05 Al _0.01 O ₂ as the positive electrode active material has a good capacity retention rate. The reason is the same as that described in Reference Example 1.

Example 4
The negative electrode active material used was a mixture of SiO having an average particle diameter of 5 μm and scaly graphite at a weight ratio of 90:10, except that the weight ratio R of the positive and negative electrode active materials shown in Table 17 was used. , to produce a cell 89-97 in the same manner as in reference example 1, was evaluated in the same manner as in reference example 1.
Table 18 shows the capacity retention rate after 500 cycles and the thermal runaway limit temperature in the heating temperature rise test for each set charge end voltage.

Similarly to Reference Example 1, even in a battery using a metal compound or a negative electrode active material mainly composed of a metal compound, the batteries 90 to 96 using the positive electrode active material of the present invention exhibit excellent cycle characteristics and safety. It was.
In particular, the batteries 91 to 96 having a positive / negative active material weight ratio R in the range of 3.0 to 19 have cycle characteristics and safety even when the charging voltage is as high as 4.25 to 4.5V. It was found to be excellent and particularly preferable. Similar results were obtained when LiNi _0.4 Mn _0.4 Co _0.2 O ₂ was used as the positive electrode active material.
Similar results were obtained when a mixture of LiCo _0.94 Mg _0.05 Al _0.01 O ₂ and LiNi _0.4 Mn _0.4 Co _0.2 O ₂ in a weight ratio of 70:30 was used as the positive electrode active material.

In LiCo _0.94 Mg _0.05 Al _0.01 O ₂ , oxides using Ti and W, Mn and Ni, Zr and Mo, respectively, instead of additive elements Mg and Al, and additive elements in LiNi _0.4 Mn _0.4 Co _0.2 O ₂ Similar results were obtained with oxides using Mg, Al, Ti, Zr, Mo or W instead of Co.
The same effect was obtained even when polytetrafluoroethylene was used as the binder for the positive electrode.

  The nonaqueous electrolyte secondary battery according to the present invention is excellent in safety, cycle characteristics and the like even when the end-of-charge voltage in a normal operating state is set to 4.25 V or more. Therefore, the nonaqueous electrolyte secondary battery of the present invention is particularly useful as a main power source for mobile communication devices and portable electronic devices.

It is the perspective view which notched the principal part of the nonaqueous electrolyte battery in a reference example and the Example of this invention. It is a block diagram which shows the structure of the charging / discharging control apparatus incorporating the battery of this invention.

Claims (15)

A negative electrode including an active material capable of inserting and extracting lithium, a positive electrode including a lithium composite oxide as an active material, a separator separating the negative electrode and the positive electrode, and a lithium ion conductive non-aqueous electrolyte, and an end-of-charge voltage Is a non-aqueous electrolyte secondary battery set to 4.4 to 4.5V,
The negative electrode active material is mainly a carbonaceous material,
The lithium composite oxide, a mixture of oxides A and the oxide B, wherein the weight ratio between the oxide A and the oxide B is 9: 1 to 1: 9,
The oxide A has the formula _{Li x Co 1-y M y} O 2 (M is Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, And at least one selected from the group consisting of W, Re, Yb, Cu, Zn, and Ba, and 1.0 ≦ x ≦ 1.15 and 0.005 ≦ y ≦ 0.1. And
The oxide B is represented by the formula _{Li x Ni y Mn z M 1} -yz O 2 (M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, At least one selected from the group consisting of W and Re, 1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 0.5, and 0.9 ≦ y / z ≦ 3.0.)
In the region where the positive electrode and the negative electrode face each other, the ratio R = Wp / Wn between the weight Wp per unit area of the active material contained in the positive electrode and the weight Wn per unit area of the active material contained in the negative electrode is 1. non-aqueous electrolyte secondary battery characterized in that in the range of 3 to 2.2.   2. The non-metal composition according to claim 1, wherein when the lithium composite oxide is a mixture of the oxide A and the oxide B, the weight ratio of the oxide A to the oxide B is 9: 1 to 5: 5. Water electrolyte secondary battery. A negative electrode including an active material capable of inserting and extracting lithium, a positive electrode including a lithium composite oxide as an active material, a separator separating the negative electrode and the positive electrode, and a lithium ion conductive non-aqueous electrolyte, and an end-of-charge voltage Is a non-aqueous electrolyte secondary battery set to 4.4 to 4.5V,
The active material of the negative electrode is mainly composed of an alloy or a metal compound,
The lithium composite oxide, an oxide A, or is a mixture of oxide B and the oxide A,
The oxide A has the formula _{Li x Co 1-y M y} O 2 (M is Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, And at least one selected from the group consisting of W, Re, Yb, Cu, Zn, and Ba, and 1.0 ≦ x ≦ 1.15 and 0.005 ≦ y ≦ 0.1. And
The oxide B is represented by the formula _{Li x Ni y Mn z M 1} -yz O 2 (M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, At least one selected from the group consisting of W and Re, 1.0 ≦ x ≦ 1.15, 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 0.5, and 0.9 ≦ y / z ≦ 3.0.)
In the region where the positive electrode and the negative electrode face each other, the ratio R = Wp / Wn between the weight Wp per unit area of the active material contained in the positive electrode and the weight Wn per unit area of the active material contained in the negative electrode is 2. range near 5 to 19 is, when the lithium composite oxide is the oxide a, the ratio R is in the range of 3.0 to 19,
When the lithium composite oxide is a mixture of oxide B and the oxide A, the weight ratio of the oxide A and the oxide B is 9: 1 to 1: 9 der non, wherein Rukoto Water electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to claim 3, wherein the negative electrode active material is selected from the group consisting of Si, Sn, Si, or an alloy containing Sn, and SiO. The lithium composite oxide is, when the oxide A is a mixture of oxide B, the weight ratio of the oxide B and the oxide A is 9: 1-5: according to claim 3 which is 5 Non-aqueous electrolyte secondary battery. The lithium composite oxide has Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Sn, Bi, Cu on the surface thereof. , Si, Ga, and at least one selected from the group consisting of B metal, according to any one of claims 1 to 5, covering the intermetallic compound containing the metal, or an oxide of the metal Non-aqueous electrolyte secondary battery. The positive electrode further comprises the formula MOx (M is Li, Co, Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, and Re. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6 , comprising an oxide represented by at least one selected from the group, wherein 0.4 ≦ x ≦ 2.0. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7 , wherein the nonaqueous electrolyte includes a cyclic carbonate and a noncyclic carbonate as a solvent. The nonaqueous electrolyte secondary battery according to claim 8 , wherein a ratio of cyclic carbonates in a solvent component of the nonaqueous electrolyte is 10 to 50% in a volume ratio at 20 ° C. The nonaqueous electrolyte, the nonaqueous electrolyte secondary battery according to any one of claims 1 to 7 including a LiPF ₆ as the lithium salt. The nonaqueous electrolyte secondary battery according to claim 10 , wherein the nonaqueous electrolyte includes 0.5 to 2.0 mol / l LiPF ₆ and 0.01 to 0.3 mol / l LiBF ₄ as lithium salts. The non-aqueous electrolyte contains cyclic carbonates and non-cyclic carbonates as a solvent, the ratio of the cyclic carbonates in the solvent component is 10 to 50% by volume, and 0.5 to 2.0 mol /% as the lithium salt. the non-aqueous electrolyte secondary battery according to any one of claims 1 to 7 including a LiPF ₆ and 0.01~0.3mol / l LiBF ₄ in l. The nonaqueous electrolyte, as an additive, according to any one of claims 1 to 12 including at least one benzene derivative containing a tertiary or quaternary carbon bearing group adjacent to the phenyl group and the phenyl group Non-aqueous electrolyte secondary battery. It said additive, cyclohexylbenzene, biphenyl, and at least one selected from the group consisting of diphenyl ether, to claim 13 the content of the non-aqueous electrolyte is from 0.05 to 8.0% by weight The nonaqueous electrolyte secondary battery as described. The nonaqueous electrolyte secondary battery according to claim 14 , wherein a content ratio of the additive in the nonaqueous electrolyte is 0.1 to 6.0% by weight.

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