JP2015115268A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a favorable charge/discharge characteristics and also having high capacity and high voltage.SOLUTION: A lithium ion secondary battery includes two or more positive electrodes and one or more negative electrodes. The positive electrodes include a first positive electrode including a positive electrode active material capable of absorbing and desorbing lithium ions at a potential of 4.3 V or less with respect to lithium and a second positive electrode including a positive electrode active material capable of absorbing and desorbing lithium ions at a potential of 4.6 V or more with respect to lithium. The first positive electrode and the second positive electrode include electrode tabs separate each other.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, in particular, a lithium ion secondary battery, and more particularly to a positive electrode using a high voltage active material and a lithium ion secondary battery using the positive electrode.

  Currently, with the spread of mobile devices such as mobile phones and notebook personal computers, the role of secondary batteries as the power source is regarded as important. These secondary batteries are compact, lightweight, have high capacity and high voltage, and are required to have performance and high safety that are resistant to deterioration even after repeated charging and discharging. Currently, lithium-ion secondary batteries are most frequently used. ing.

  A transition metal oxide mainly containing Li is used for the positive electrode of the lithium ion secondary battery. Currently, most of those that are put into practical use as positive electrodes have a redox potential of about 4 V with respect to the redox potential of Li. In the future, it is necessary to increase the potential in order to significantly improve the energy density, and positive electrode materials having a redox potential of about 5 V with respect to the redox potential of Li have been studied.

As a positive electrode material capable of realizing an oxidation-reduction potential of about 5 V, for example, by using a spinel compound in which Mn of lithium manganate is substituted with Ni or the like, such as LiNi _0.5 Mn _1.5 O ₄ , as an active material, It is known that a 5V class operating potential can be realized (Patent Document 1). The positive electrode using LiNi _0.5 Mn _1.5 O ₄ can perform a redox reaction at about 4.7 V with respect to the redox potential of Li, and is used in applications that require high voltage output. Expected to be used.

However, with respect to the Li storage amount, LiNi _0.5 Mn _1.5 O ₄ has a problem that the amount of Li per unit weight is smaller and the capacity is lower than LiNiO ₂ which has been put into practical use. By using together a 5V-class positive electrode material such as LiNi _0.5 Mn _1.5 O ₄ as described above and a high-capacity 4V-class positive electrode material, an active material having a good balance between high voltage and high capacity is obtained. Expected to be able to.

  As a secondary battery using a 4V class positive electrode material and a 5V class positive electrode material, for example, in Patent Document 2, a non-aqueous electrolyte secondary battery using a positive electrode containing one or more 4V class composite oxides, A non-aqueous electrolyte secondary battery containing a 5V class composite oxide in the positive electrode is described, and it is described that the 5V class composite oxide functions as a buffer in an overvoltage region of 4.2 V or higher.

  On the other hand, Patent Document 3 describes a battery incorporating a first positive electrode and a second positive electrode having different potentials. Patent Document 4 discloses a stacked type in which the cathode active material and / or the anode active material have different compositions so as to cause a voltage difference, and different electrode terminals are attached to the battery case according to the voltage difference. A secondary battery is described.

JP 2009-123707 A JP 2002-208441 A Japanese Patent Laid-Open No. 11-135151 Special table 2009-540523

  However, the secondary batteries described in Patent Documents 3 and 4 do not use a positive electrode active material that operates at a high potential, and the voltage that can be supplied by these secondary batteries is limited.

In addition, when a 5V-class positive electrode material and a 4V-class positive electrode material are mixed and used as a positive electrode active material, as described in Patent Document 2, a positive electrode material having a layered structure such as LiNiO ₂ is There is a problem that Li is excessively released in a high voltage state, structural transition occurs, and charging / discharging stops. Therefore, in the secondary battery described in Patent Document 2, it is considered difficult to achieve both high capacity and high voltage.

  In view of the above problems, an object of the present invention is to provide a nonaqueous electrolyte secondary battery having a high voltage and a high capacity.

One embodiment of the present invention provides:
A lithium ion secondary battery comprising two or more positive electrodes and one or more negative electrodes,
The positive electrode is
A first positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.3 V or less with respect to lithium;
A second positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or higher with respect to lithium;
Including
The first positive electrode and the second positive electrode each have a separate electrode tab, and relate to a lithium ion secondary battery.

  According to the present invention, a nonaqueous electrolyte secondary battery having a high voltage and a high capacity can be provided.

It is sectional drawing of the battery which concerns on one Embodiment of this invention. It is an external view of the battery which concerns on one Embodiment of this invention.

  In the nonaqueous electrolyte secondary battery according to the present invention, the positive electrode includes a first positive electrode including a 4V class positive electrode material (positive electrode active material) and a second positive electrode including a 5V class positive electrode material (positive electrode active material). The first positive electrode and the second positive electrode have a structure including separate electrode tabs.

  The first positive electrode and the second positive electrode are provided with separate electrode tabs, whereby the first positive electrode including the 4V class positive electrode material and the second positive electrode including the 5V class positive electrode material are separately charged. Therefore, the 4V class positive electrode material is not deteriorated due to the structural phase transition when a high voltage is applied. Further, in the secondary battery according to the embodiment of the present invention, it is possible to switch to either the 4V class or 5V class output as necessary, and the 4V class and 5V class outputs are used simultaneously. It is also possible.

[Positive electrode]
(First positive electrode)
The first positive electrode includes a positive electrode active material capable of causing a redox reaction at a potential of 4.3 V or less with respect to a redox potential of lithium as a positive electrode active material. Such a positive electrode active material is not particularly limited, but a 4V class positive electrode material is preferable. In the present invention, the term “4V class positive electrode material” represents a positive electrode active material having an operating potential of 4.3 V or less, preferably 3.6 V or more and 4.3 V or less with respect to the redox potential of lithium. The 4V class positive electrode material according to the present embodiment is preferably a lithium-containing composite oxide, and is not particularly limited. However, lithium manganate having a spinel structure such as Li _x Mn ₂ O ₄ (0 <x <2), LiMnO Lithium transition metal oxide having a layered structure such as Li ₂ , LiCoO ₂ , LiNiO _{2 and the} like, in which some of these transition metals are replaced with other metals; LiNi _1/3 Co _1/3 Mn _1/3 O _2, etc. Lithium transition metal oxides in which the number of specific transition metals does not exceed half; those lithium transition metal oxides in which Li is excessive in excess of the stoichiometric composition. Further, these metal oxides were partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. Materials can also be used. In _{particular, Li α Ni β Co γ Al} δ O 2 (1 ≦ α ≦ 2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0.2) or _{Li α Ni β Co γ Mn δ} O 2 (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6, γ ≦ 0.2).

  These positive electrode active materials can be used individually by 1 type or in combination of 2 or more types.

  In the first positive electrode, the content of the 4V class positive electrode material is preferably 90% by weight or more of the positive electrode active material of the first positive electrode, more preferably 95% by weight or more, and 100% by weight. It may be.

(Second positive electrode)
The second positive electrode includes a 5V class positive electrode material as a positive electrode active material. In the present invention, the term “5V class positive electrode material” refers to a positive electrode active material capable of inserting and extracting lithium ions at a potential of 4.5 V or higher, preferably 4.6 V or higher with respect to the redox potential of lithium. . The 5V class positive electrode material according to the present embodiment is preferably a lithium-containing composite oxide, for example, lithium manganese having a spinel structure such as Li _x Mn _1.5 Ni _0.5 O ₄ (0 <x <1). A composite oxide is mentioned. Also, this metal oxide is partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. For example, the formula:
_{Li a (M x Mn 2-} x-y A y) (O 4-w Z w)
(Wherein 0.4 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1, and M is Co, Ni, Fe, Cr and Cu A is at least one selected from the group consisting of Li, B, Na, Mg, Al, Ti, Si, K and Ca, and Z is F and Cl At least one of them) may be used.

As another example of the 5V class positive electrode material according to the present embodiment, for example, Li _x MPO ₄ F _y (0 ≦ x ≦ 2, 0 ≦ y ≦ 1, M is at least one of Co and Ni. Si-containing composite oxide represented by Li _x MSiO ₄ (0 ≦ x ≦ 2, M is at least one of Mn, Fe, and Co). Etc.

Since a high voltage is applied to the second positive electrode during charging, the content of the positive electrode active material such as LiNiO _{2 that} deteriorates due to a structural change under a high voltage is low or included from the viewpoint of increasing the energy density. Preferably not. The content of the 5V class positive electrode material in the second positive electrode is preferably 95% by weight or more of the positive electrode active material of the second positive electrode, more preferably 97% by weight or more, and 100% by weight. There may be. Among 5V class positive electrode materials, a positive electrode active material having a spinel structure such as LiNi _0.5 Mn _1.5 O ₄ is preferably used from the viewpoint of structural stability in a charged state.

  In the secondary battery according to the present embodiment, the content of the 5V class positive electrode material is generally less than 50% by weight and 30% by weight or less with respect to the whole positive electrode active material included in the secondary battery. Preferably, it is 20% by weight or less. Moreover, it is preferable that it is 5 weight% or more with respect to the whole positive electrode active material contained in a secondary battery, and it is more preferable that it is 10 weight% or more. By including 5% by weight or more of the 5V class positive electrode material operating at a higher potential with respect to the positive electrode active material, a high voltage can be supplied. On the other hand, when the content of the 5V class positive electrode material is less than 50% by weight of the positive electrode active material, it is preferable because good cycle characteristics can be maintained and a high capacity can be secured.

  In the secondary battery according to the present embodiment, the ratio of the content of the 4V class positive electrode material and the 5V class positive electrode material can be adjusted by changing the content of the positive electrode active material included in each positive electrode, or As will be described later, the adjustment can be made by changing the number of the first positive electrode and the second positive electrode.

  The positive electrode according to the present embodiment includes a positive electrode active material, a conductivity imparting agent such as carbon black or acetylene black for imparting conductivity as required, and a binder resin, and a mixture of these (electrode material) ) To form an active material layer of the positive electrode.

  The positive electrode for a secondary battery according to the present embodiment can be produced, for example, by a method in which a positive electrode active material is mixed with a conductivity-imparting agent and a binder is further mixed and applied onto a current collector.

  The binder for the positive electrode (binder) is not particularly limited. For example, poly (vinylidene fluoride), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetra And fluoroethylene. Examples of the conductive agent include carbon black and acetylene black. As the positive electrode current collector, aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used. The thickness of the metal foil of the positive electrode current collector is preferably such that the strength can be maintained, and is preferably 4 to 100 μm. Moreover, in order to raise an energy density, it is more preferable that it is 5-30 micrometers.

[Negative electrode]
The negative electrode active material according to the present invention is not particularly limited, and various carbon materials, oxides, lithium alloys and the like can be used.

  Examples of the carbon material include carbon materials that perform charging and discharging, such as amorphous carbon such as graphite and hard carbon, diamond-like carbon, and carbon nanotubes. Among these, graphite or amorphous carbon is preferable. In particular, graphite has high electron conductivity, excellent adhesion to a current collector made of a metal such as copper, and voltage flatness. Since it is formed at a high processing temperature, it contains few impurities and improves negative electrode performance. Advantageous and preferred. These may use only 1 type and may use 2 or more types together.

  Examples of the oxide include silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and composites thereof. In particular, silicon oxide is preferably included. The structure is preferably in an amorphous state.

  The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. The lithium alloy is, for example, a binary or ternary alloy of a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and lithium. And can be formed by a known method. The lithium metal and lithium alloy are particularly preferably amorphous. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects.

  In the present embodiment, the negative electrode active material preferably includes at least one carbon material, and may be composed of only a carbon material.

  As a method for producing the negative electrode, specifically, an active material such as carbon powder, a binder, and, if necessary, a carbon material as a conductivity imparting agent, N-methyl-2-pyrrolidone (NMP And the like, and the kneaded product is coated on a negative electrode current collector made of a metal foil and dried in a high temperature atmosphere. Examples of the conductivity-imparting agent include carbon materials such as acetylene black, carbon black, fibrous carbon, graphite, and conductive oxide powder. The binder is not particularly limited, and a known material can be used. For example, polyvinylidene fluoride (PVDF) can be used. As the current collector, a metal foil mainly composed of Al, Cu or the like can be used.

  In this embodiment, the negative electrode may be composed of one or more negative electrodes having a single operating potential, or composed of two or more negative electrodes having different operating potentials. It may be.

[Electrolyte]
Nonaqueous electrolytic solvents for the electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, and γ-lactones such as γ-butyrolactone, Chain ethers such as 2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, Dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate Aprotic organic solvents such as derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole and N-methylpyrrolidone can be used singly or in combination.

  Since the secondary battery according to the present embodiment includes a positive electrode active material that operates at a high potential, it is also preferable to use a solvent having high voltage resistance as the nonaqueous electrolytic solvent. Examples of the solvent having high voltage resistance include fluorinated solvents such as fluorinated phosphates and fluorinated ethers, and sulfone compounds. Solvents with high voltage resistance can be used singly or in combination of two or more.

  In one embodiment, the non-aqueous electrolytic solvent may include a fluorinated phosphate ester represented by the following formula (1).

(Wherein R ¹ , R ² and R ³ each independently represents an alkyl group or a fluorinated alkyl group, and at least one of R ¹ , R ² and R ³ is a fluorinated alkyl group.)

In the formula (1), the fluorinated alkyl group is an alkyl group having at least one fluorine atom. In the formula ^(1), the number of carbon atoms in R 1, ^{R 2} and ^{R 3} each independently is preferably 1-3. At least one of R ¹ , R ² and R ³ is preferably a fluorinated alkyl group in which 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl group are substituted with fluorine atoms. When the content of fluorine atoms in the fluorinated phosphate ester is large, the voltage resistance is further improved, and even when a 5V class positive electrode material is used, a decrease in battery capacity after a charge / discharge cycle can be reduced.

  Examples of the fluorinated phosphate ester include tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), tris phosphate (2,2,2-trifluoroethyl) (TTFP), tris phosphate ( Fluorinated alkyl such as 2,2,3,3-tetrafluoropropyl), tris phosphate (3,3,3-trifluoropropyl), tris phosphate (2,2,3,3,3-pentafluoropropyl) Examples of the phosphoric acid ester compound include tris phosphate (2,2,2-trifluoroethyl).

  The higher the content of the fluorinated phosphate ester, the better the oxidation resistance of the nonaqueous electrolytic solvent. Therefore, the content of the fluorinated phosphate ester is preferably 5% by volume or more in the nonaqueous electrolytic solvent. It is preferable that it is volume% or more. On the other hand, if the content of the fluorinated phosphate is too large, the ionic conductivity decreases due to an increase in the viscosity of the electrolytic solution or a decrease in the dielectric constant. Therefore, the content of the fluorinated phosphate is 70 volumes in the nonaqueous electrolytic solvent. % Or less is preferable.

  In one embodiment, the nonaqueous electrolytic solvent may include a fluorinated ether represented by the following formula (2).

(Wherein R ₁₀₁ and R ₁₀₂ each independently represents an alkyl group or a fluorinated alkyl group, and at least one of R ₁₀₁ and R ₁₀₂ is a fluorinated alkyl group.)

In the formula (2), the total number of carbon atoms of R ₁₀₁ and R ₁₀₂ is preferably 10 or less. The alkyl group and the fluorinated alkyl group include linear or branched ones.

  In the formula (2), the fluorinated alkyl group represents an alkyl group having at least one fluorine atom. When the content of fluorine atoms is large, the voltage resistance is further improved, and it is possible to more effectively reduce the deterioration of the battery capacity after the charge / discharge cycle even when a 5V class positive electrode material is used. Therefore, the fluorine atom content of the fluorinated alkyl group is preferably 50% or more with respect to the total of fluorine atoms and hydrogen atoms.

  Among these, a fluorinated ether represented by the following formula (3) is preferable from the viewpoint of voltage resistance and compatibility with other electrolytes.

^{X 1 - (CX 2 X 3} ) n-O- (CX 4 X 5) m-X 6 (3)
(In the formula, n and m are each independently 1 to 8. X ^{1 to} X ⁶ are each independently a fluorine atom or a hydrogen atom, and at least one of X ^{1 to} X ⁶ is a fluorine atom. When at least one of n and m is 2 or more, a plurality of X ² , X ³ , X ⁴ and X ⁵ may be independent from each other.

  Examples of the fluorinated ether include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,4,4,4-hexafluorobutyl-difluoro. Methyl ether, 1,1-difluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,1,2,3,3-hexafluoropropyl-2,2-difluoroethyl ether, 1,1 -Difluoroethyl-1H, 1H-heptafluorobutyl ether, 1H, 1H, 2'H, 3H-decafluorodipropyl ether, bis (2,2,3,3,3-pentafluoropropyl) ether, 1H, 1H, 5H-perfluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis (1H, 1H-heptafluorobutyl) ether 1H, 1H, 2′H-perfluorodipropyl ether, 1,1,2,3,3,3-hexafluoropropyl-1H, 1H-heptafluorobutyl ether, 1H-perfluorobutyl-1H-perfluoroethyl Examples include ether. Among these, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is preferable.

  By containing the fluorinated ether, the oxidation resistance of the electrolytic solution is increased and the viscosity is decreased. On the other hand, if the content of the fluorinated ether is too large, the dielectric constant of the electrolytic solution and the compatibility with other nonaqueous electrolytic solvents may be lowered. Accordingly, the content of the fluorinated ether compound represented by the formula (3) is preferably 10% by volume or more and 70% by volume or less in the nonaqueous electrolytic solvent, and preferably 30% by volume or more and 60% by volume or less. More preferred.

  As fluorinated solvents other than fluorinated phosphates and fluorinated ethers, some or all of hydrogen atoms such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinylene carbonate (VC) may be used. Fluorinated cyclic carbonate substituted with fluorine atoms; some or all of hydrogen atoms such as ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), etc. were substituted with fluorine atoms Fluorinated chain carbonate; fluorinated carboxylate in which some or all of the hydrogen atoms of ethyl acetate, methyl propionate, ethyl formate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetate and methyl formate are substituted with fluorine atoms Etc. It can not limited thereto.

  In one embodiment, the nonaqueous electrolytic solvent may contain a sulfone compound represented by the following formula (4).

(Wherein R ₁ and R ₂ each independently represent a substituted or unsubstituted alkyl group, and R ₁ and R ₂ are cyclic compounds in which carbon atoms of R ₁ and R ₂ are bonded via a single bond or a double bond, Is also good.)

In the formula (4), it is preferable that the carbon number n2 carbon atoms n1, _{R 2} of _{R 1} is 1 ≦ n1 ≦ 12,1 ≦ n2 ≦ 12 , respectively, at 1 ≦ n1 ≦ 6,1 ≦ n2 ≦ 6 More preferably, it is more preferable that 1 ≦ n1 ≦ 3 and 1 ≦ n2 ≦ 3. The alkyl group may be linear, branched or cyclic.

R ₁ and R ₂ may have a substituent. Examples of the substituent include an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, and a halogen atom (for example, a chlorine atom and a bromine atom). , Fluorine atom) and the like.

  Examples of the sulfone compounds include sulfolane (tetramethylene sulfone), 3-methyl sulfolane, dimethyl sulfone (for example, 3,4-dimethyl sulfone, 2,5-dimethyl sulfone), ethyl methyl sulfone, diethyl sulfone, butyl methyl sulfone, pentamethylene sulfone. , Hexamethylene sulfone, ethylene sulfone, trimethylene sulfone and the like.

  The content of the sulfone compound is preferably from 0.1 to 70% by volume, more preferably from 1 to 65% by volume, and even more preferably from 3 to 60% by volume of the non-aqueous electrolyte from the viewpoint of compatibility and viscosity of the electrolyte. .

Lithium salts are dissolved in these nonaqueous electrolytic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CCF ₃ SO ₂ ). ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides and the like.

  Further, a polymer electrolyte may be used instead of the electrolytic solution.

[Configuration of secondary battery]
The configuration of the secondary battery according to the present embodiment is particularly limited as long as it is a configuration in which an electrode element composed of two or more positive electrodes and one or more negative electrodes and an electrolytic solution are included in the outer package. It can be a cylindrical shape, a wound shape, a stacked shape, a coin shape or the like. Among these, from the viewpoint of easily forming a structure in which two types of positive electrodes are bundled and taking out current separately, a stacked type in which positive electrodes and negative electrodes are alternately stacked via separators may be used. preferable.

  The arrangement of the positive electrode and the negative electrode in the electrode element is not particularly limited. For example, the same electrode may be arranged at both ends of the electrode element, such as “negative electrode / positive electrode / negative electrode / positive electrode / negative electrode”. Or it is good also as a structure by which a positive electrode and a negative electrode are each arrange | positioned at the both ends of an electrode element like "positive electrode / negative electrode / positive electrode / negative electrode". It is good also as a structure containing 2 or more of 1st positive electrodes and 2nd positive electrodes, respectively. By changing the number of the first positive electrode and the second positive electrode, the ratio of the content of the 4V class positive electrode material and the 5V class positive electrode material included in the secondary battery according to the present embodiment can be easily changed. it can. The number of negative electrodes can be appropriately determined according to the number of positive electrodes.

  In the present embodiment, the first positive electrode and the second positive electrode each have separate electrode tabs. Therefore, as shown in FIG. 2, it is preferable to arrange the first positive electrode tab and the second positive electrode tab so as not to short-circuit each other when the electrode element is configured. In an embodiment in which each of the first positive electrode and the second positive electrode includes a plurality of positive electrodes, the plurality of first positive electrodes and the plurality of second positive electrodes are separately focused, and the first positive electrode tab The second positive electrode tab is preferably arranged so as not to short-circuit each other. As described above, the first positive electrode tab and the second positive electrode tab are independent from each other, so that the charge and discharge of the first positive electrode and the second positive electrode can be performed separately. Become. For example, depending on the required operating voltage, the first positive electrode and the second positive electrode can be used to supply 4V class and 5V class operating voltages simultaneously, or the first positive electrode Either one of the electrode and the second positive electrode can be used to supply an operating voltage of either 4V class or 5V class.

(Production method of secondary battery)
As a method for manufacturing the secondary battery according to the present embodiment, for example, in a dry air or inert gas atmosphere, the first positive electrode, the second positive electrode, and the negative electrode according to the present embodiment are interposed via a separator. The laminated body can be produced by being housed in a battery can. Further, the laminate can be produced by sealing with a flexible film or the like in which a synthetic resin and a metal foil are laminated.

(How to charge the secondary battery)
The charging method of the secondary battery according to the present embodiment is not particularly limited. However, since the first positive electrode tab and the second positive electrode tab are independent as described above, Charging can be performed by applying different voltages to the positive electrode and the second positive electrode. For example, a charging voltage can be applied to the first positive electrode so that the charging upper limit voltage is 4.3 V or less, preferably 3.6 V or more and 4.3 V or less. On the other hand, a charging voltage can be applied to the second positive electrode so that the charging upper limit voltage is 4.5 V or more, preferably 4.6 V or more and 5.5 V or less.

  As a charging method, the first positive electrode and the second positive electrode may be charged at the same time, but the first positive electrode is charged first under the condition that the charge upper limit voltage is 4.3 V or less, and then charged. It is also preferable to charge the second positive electrode under the condition that the upper limit voltage is 4.6 V or higher.

(Production of first positive electrode)
In this example, LiNi _0.8 Co _0.15 Al _0.05 O ₂ was used as the positive electrode active material of the first positive electrode. This material is commercially available as a powder reagent, and these powders were obtained and used. When the charge / discharge performance was confirmed (capacity characteristics were confirmed between 4.3 V and 3.0 V by a model cell using metal lithium as a counter electrode), it showed about 220 mAh / g, and the charge / discharge potential was around 3.7 V. It was. After applying an electrode material mixed with 96% by mass of the active material particles, 4% by mass of polyvinylidene fluoride as a binder, and NMP as a solvent on a 20 μm aluminum foil, and performing a drying treatment at 125 ° C. for 5 minutes. Then, compression molding was performed with a roll press. The active material layer formed on the aluminum foil was punched into a size of 28 × 26 mm to be a positive electrode, and a positive electrode lead tab made of aluminum for taking out electric charges was fused by ultrasonic waves.

(Production of second positive electrode)
In this example, LiNi _0.5 Mn _1.5 O ₄ was used as the positive electrode active material of the second positive electrode. This material is commercially available as a powder reagent, and these powders were obtained and used. When the charge / discharge performance was confirmed (capacity characteristics were confirmed between 4.85 V and 3.0 V using a model cell with metallic lithium as a counter electrode), it showed about 130 mAh / g, and the charge / discharge potential was around 4.75 V. It was. After applying an electrode material mixed with 96% by mass of the active material particles, 4% by mass of polyvinylidene fluoride as a binder, and NMP as a solvent on a 20 μm aluminum foil, and performing a drying treatment at 125 ° C. for 5 minutes. Then, compression molding was performed with a roll press. The active material layer formed on the aluminum foil was punched into a size of 28 × 26 mm to be a positive electrode, and a positive electrode lead tab made of aluminum for taking out electric charges was fused by ultrasonic waves.

(Preparation of negative electrode)
In this example, graphite powder was used as the negative electrode active material. An electrode material mixed with 98.5% by mass of graphite, 1.5% by mass of SBR as a binder, and water as a solvent was applied onto a 10 μm copper foil, dried at 80 ° C. for 5 minutes, and then subjected to compression molding with a roll press. went. The active material layer formed on the copper foil was punched out to 30 × 28 mm to form a negative electrode, and a negative electrode lead tab made of nickel for extracting electric charge was fused by ultrasonic waves.

(Production of model battery)
In order of the negative electrode, separator, first positive electrode, separator, negative electrode, separator, second positive electrode, and separator, five negative electrodes and two first positive electrodes so that the active material layer faces the separator Then, after laminating two second positive electrodes, this was sandwiched between laminate films, an electrolytic solution was injected, and sealing was performed under vacuum to produce a laminate type battery. Note that the electrolytic solution, EC and DEC in a volume ratio of 3: was prepared by dissolving of LiPF ₆ 1 mol / L to 7 mixed solvent.

  When manufacturing this laminate type battery, the battery was prepared so that the ratio of the negative electrode charge capacity to the positive electrode charge capacity (negative electrode / positive electrode) was about 1.35. The positive electrode was prepared by changing the amount of the electrode material applied so that the weight ratio of the active material of the first positive electrode and the active material of the second positive electrode included in the battery was the ratio shown in Table 1.

  In the fabricated battery, a current was passed between the first positive electrode and the negative electrode to charge to 4.2 V, and at the same time, a current was passed between the second positive electrode and the negative electrode to charge to 4.75 V. Then, each was discharged to 3.0V and the charge / discharge efficiency was confirmed.

  The charge / discharge efficiency and the value of the discharge capacity per weight of the active material including the active material of the first positive electrode and the active material of the second positive electrode are shown.

  The volume energy density of the battery of Example 1 is shown.

(Comparative Examples 1-3)
In preparing the comparative battery, the first positive electrode active material powder and the second positive electrode active material powder were mixed to obtain positive electrode active material particles.

LiNi _0.5 Mn _1.5 O ₄ powder and LiNi _0.8 Co _0.15 All _0.05 O ₂ powder are mixed at a weight ratio of 50:50, 80:20, and 90:10, respectively, and used as active material particles. did. An electrode material in which 96% by mass of an active material, 4% by mass of polyvinylidene fluoride as a binder, and NMP as a solvent are mixed is applied onto a 20 μm aluminum foil, dried at 125 ° C. for 5 minutes, and then rolled. Compression molding was performed with a press. The active material layer formed on the aluminum foil was punched out to 28 × 26 mm and used as a comparative positive electrode, and a positive electrode lead tab made of aluminum for taking out electric charges was fused by ultrasonic waves.

After laminating five negative electrodes and four comparative positive electrodes so that the active material layer faces the separator in this order, the negative electrode, separator, comparative positive electrode, separator, and negative electrode used in the examples, The laminate type battery for comparison was prepared by sandwiching between and laminating the film, injecting an electrolytic solution, and sealing under vacuum. Note that the electrolytic solution, a volume ratio of 3 between the EC and DEC: was prepared by dissolving of LiPF ₆ 1 mol / L in a mixed solvent of 7.

  In the manufactured comparative battery, a current was passed between the comparative positive electrode and the negative electrode, and the battery was charged to 4.75V. Then, it discharged to 3.0V and confirmed charging / discharging efficiency.

  The charge / discharge efficiency of the comparative battery and the value of the discharge capacity per weight of the active material of the comparative positive electrode are shown.

(Comparative Example 4)
As a comparative example, a battery was fabricated using the first positive electrode and the second positive electrode separately as follows.

  In the same manner as in Example 1, a first positive electrode and a second positive electrode were produced. A battery using the first positive electrode and the second positive electrode in the same manner as in Example 1 except that the two produced first positive electrodes or two second positive electrodes were used as the positive electrodes. A battery using was manufactured. Thereafter, the two produced batteries were connected to form one battery.

  The volume energy density of the battery of Comparative Example 4 is shown.

  A positive electrode composed of a first positive electrode including a 4V class positive electrode material and a second positive electrode including a 5V class positive electrode material, wherein the first positive electrode and the second positive electrode have separate electrode tabs; As shown in the examples shown in Tables 1 and 2, the battery according to the present invention having the structure provided has confirmed that it has better charge / discharge characteristics and higher volume energy density than the comparative example.

1 negative electrode active material layer 2 negative electrode current collector 3 separator 4 laminate 5 first positive electrode tab 6 second positive electrode tab 7 second positive electrode active material layer 8 negative electrode tab 9 positive electrode current collector 10 first Positive electrode active material layer

Claims (10)

A lithium ion secondary battery comprising two or more positive electrodes and one or more negative electrodes,
The positive electrode is
A first positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.3 V or less with respect to lithium;
A second positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or higher with respect to lithium;
Including
The lithium ion secondary battery, wherein the first positive electrode and the second positive electrode each have a separate electrode tab.   The lithium ion secondary battery according to claim 1, wherein the positive electrode and the negative electrode are of a stacked type in which the positive electrode and the negative electrode are alternately stacked via separators.   The content of the positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or more with respect to the lithium is 5 wt% or more and 20 wt% or less of the entire positive electrode active material. The lithium ion secondary battery described in 1. The positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or higher with respect to lithium is represented by the following formula:
_{Li a (M x Mn 2-} x-y A y) (O 4-w Z w)
(Wherein 0.4 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1, and M is Co, Ni, Fe, Cr and Cu A is at least one selected from the group consisting of Li, B, Na, Mg, Al, Ti, Si, K and Ca, and Z is F and Cl The lithium ion secondary battery according to any one of claims 1 to 3, which is represented by at least one of them.   The lithium ion secondary battery of any one of Claims 1-4 whose negative electrode active material of the said negative electrode is a carbon material.   The lithium ion secondary battery according to any one of claims 1 to 5, wherein each of the first positive electrode and the second positive electrode is composed of two or more positive electrodes.   The lithium ion secondary battery according to any one of claims 1 to 6, wherein two or more operating voltages are supplied simultaneously. A method for charging a lithium ion secondary battery comprising two or more positive electrodes and one or more negative electrodes,
The positive electrode is
A first positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.3 V or less with respect to lithium;
A second positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or higher with respect to lithium;
Including
Each of the first positive electrode and the second positive electrode includes separate electrode tabs,
The lithium ion secondary battery is charged so that a charging upper limit potential of the first positive electrode is 4.3 V or less and a charging upper limit potential of the second positive electrode is 4.6 V or more. Charging method.   The method for charging a lithium ion secondary battery according to claim 8, wherein the second positive electrode is charged after the first positive electrode is charged. A method for producing a lithium ion secondary battery comprising two or more positive electrodes and one or more negative electrodes,
A first positive electrode including a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.3 V or less with respect to lithium is manufactured, and a first positive electrode tab is fused to the first positive electrode. And a process of
A second positive electrode containing a positive electrode active material capable of occluding and releasing lithium ions at a potential of 4.6 V or higher with respect to lithium is produced, and a second positive electrode tab is fused to the second positive electrode. And a process of
Producing a negative electrode and fusing a negative electrode tab;
Arranging the first positive electrode, the second positive electrode, and the negative electrode through a separator to produce an electrode element;
Encapsulating the electrode element and the electrolyte in an exterior body;
The manufacturing method of the lithium ion secondary battery containing this.