JP2004241339A - Electrolyte liquid for secondary battery, and secondary battery of nonaqueous electrolyte liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for suppressing capacity drop accompanying with cycles and deterioration of reliability at high temperature of a nonaqueous electrolyte liquid secondary battery, and improving an operation voltage of the battery. <P>SOLUTION: The nonaqueous electrolyte battery uses a positive electrode activator storing and releasing for storing Li at a voltage of 4.5 V or higher, and the electrolyte liquid contains carbonic acid ester substituted by halogen or chain-shaped carboxylic acid ester of which main skeleton carbon is saturated. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００７９】
表１から明らかなように、４．５Ｖ以上でＬｉを吸蔵放出する正極活物質を使用し、電解液の溶媒として主骨格炭素が飽和しているフッ素置換炭酸エステルまたは鎖状カルボン酸エステルを含むことにより、サイクル特性が改善することが確認された。
【００８０】
【発明の効果】
以上説明したように本発明によれば、４．５Ｖ以上でＬｉを吸蔵放出する正極活物質を使用し、電解液中に主骨格炭素が飽和しているハロゲン置換炭酸エステルまたは鎖状カルボン酸エステルを含むことにより、非水電解液二次電池のサイクルに伴う容量低下や、高温での信頼性の低下が抑制される。また、本発明のによれば、非水電解液二次電池の動作電圧が向上する。
【図面の簡単な説明】
【図１】本実施形態に係る二次電池の構成を示す断面図である。
【符号の説明】
１ 正極活物質層
２ 負極活物質層
３ 正極集電体
４ 負極集電体
５ 多孔質セパレータ
６ 正極外装缶
７ 負極外装缶
８ 絶縁パッキング部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrolyte for a secondary battery and a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
Lithium ion secondary batteries are widely used for applications such as portable electronic devices and personal computers. It is also expected to be applied to automotive applications in the future. In these applications, miniaturization and weight reduction of the battery have been conventionally required, but on the other hand, increasing the energy density of the battery is an important technical problem.
[0003]
There are several methods for increasing the energy density of the lithium ion secondary battery. Among them, raising the operating potential of the battery is an effective means. In a conventional lithium ion secondary battery using lithium cobaltate or lithium manganate as a positive electrode active material, the operating potential is 4 V class (average operating potential = 3.6 to 3.8 V: potential relative to lithium). This is due to the redox reaction of Co ions or Mn ions (Co^{3 +}← → Co⁴⁺Or Mn^{3 +}← → Mn⁴⁺) Defines the expression potential. On the other hand, it is known that a 5-V class operating potential can be realized by using, as an active material, a spinel compound in which Mn of lithium manganate is substituted by Ni or the like. Specifically, LiNi_{0. 5}Mn_{1. 5}O₄It is known that a potential plateau is exhibited in a region of 4.5 V or more by using a spinel compound such as In such a spinel compound, Mn exists in a tetravalent state,³⁺← → Mn⁴⁺Ni instead of redox²⁺← → Ni⁴⁺The operating potential is defined by the oxidation-reduction of.
[0004]
LiNi_{0. 5}Mn_1.5O₄Has a capacity of 130 mAh / g or more and an average operating voltage of 4.6 V or more with respect to Li metal. The capacity is LiCoO₂Although smaller, the energy density of the battery is LiCoO₂Higher than. For this reason, LiNi_0.5Mn_1.5O₄Is promising as a future cathode material. For example, for a device that conventionally used a plurality of batteries, by using a secondary battery having an operating potential of 5V class and increasing the voltage, the number of batteries used can be reduced and the energy density can be improved. it can.
[0005]
However, LiNi_0.5Mn_1.5O₄Battery using a high-voltage positive electrode material such as LiCoO₂It has been found that, as compared with a battery using such as a positive electrode active material, deterioration accompanied by a decrease in charge / discharge cycles or capacity when left in a charged state is more likely to occur. It is considered that the main cause of the capacity deterioration accompanying the cycle is that decomposition products of the electrolytic solution are generated on the positive electrode side, and the decomposition products are deposited on the negative electrode side by the charge / discharge cycle. In particular, since the battery is liable to be deteriorated at a temperature of about 50 ° C., there is a demand for a battery that can suppress the deterioration even at an operation of about 50 ° C.
[0006]
Therefore, by adding hexamethylenetetramine to the electrolyte, the amount of HF in the electrolyte is reduced, and LiMn is added.₂O₄A technique for suppressing the elution of Mn from methane has been proposed (Patent Document 1). However, in the electrolyte described in Patent Document 1, the decomposition of the electrolyte in the positive electrode could not be suppressed.
[0007]
In addition, a technique has been proposed in which a halogen-substituted chain ester is used as a solvent for an electrolytic solution to improve the oxidation resistance and the charge / discharge cycle of the electrolytic solution (Patent Document 2). However, when a halogen-substituted chain ester is used under the conditions of Patent Literature 2, the viscosity of the electrolytic solution is high, and the conductivity of the electrolytic solution is reduced.
[0008]
Patent Document 3 proposes a method using an electrolytic solution containing a vinylene carbonate derivative having an electron-withdrawing group. Patent Document 4 discloses an electrolytic solution containing a cyclic carbonate, an asymmetric chain carbonate, and a carboxylic acid ester. Has been proposed. However, even with these methods, it was not possible to sufficiently improve the cycle characteristics of a secondary battery having a 5 V class operating potential.
[0009]
[Patent Document 1]
JP 2001-266940 A
[Patent Document 2]
JP-A-7-6786
[Patent Document 3]
JP 2001-35530 A
[Patent Document 4]
JP-A-2002-305035
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for suppressing a decrease in capacity due to a cycle of a nonaqueous electrolyte secondary battery and a decrease in reliability at a high temperature. Another object of the present invention is to provide a technique for increasing the operating voltage of a non-aqueous electrolyte secondary battery.
[0011]
[Means for Solving the Problems]
According to the present invention, there is provided an electrolyte solution for a secondary battery, comprising an electrolyte and a chain carboxylic acid ester.
[0012]
Further, according to the present invention, there is provided a secondary battery including a cathode active material having an average discharge potential of 4.5 V or more with respect to Li metal, and an electrolyte, wherein the electrolyte is composed of an electrolyte and a chain carboxylic acid. A non-aqueous electrolyte secondary battery comprising an ester is provided.
[0013]
In the present invention, since the chain carboxylic acid ester is contained in the organic solvent constituting the electrolytic solution, capacity deterioration can be reduced. Further, output characteristics at the time of large current discharge can be improved. It is presumed that the reason for this is that when a chain carboxylic acid ester is contained, the conductivity of the electrolytic solution increases and polarization decreases.
[0014]
Further, as a result of the study by the present inventors, it has been found that when a positive electrode which is charged and discharged at 4.5 V or more is used, these battery characteristics are significantly improved. A battery having a discharge potential of 4.5 V or more has a long period of time during which the electrolyte is present at a high voltage, and the decomposition reaction of the electrolyte is promoted. For this reason, the capacity deterioration accompanying the decomposition of the electrolytic solution is particularly remarkable. A battery having a discharge potential of 4.5 V or more has a larger amount of decomposition products deposited on the negative electrode than a battery charged and discharged at 4.5 V, and capacity degradation occurs due to an increase in resistance on the negative electrode side. Although this is easy, by containing a chain carboxylic acid ester in the electrolytic solution, this can be suitably mitigated.
[0015]
In the electrolyte solution for a secondary battery of the present invention, the chain carboxylate may be contained in an amount of 0.01% by volume or more and 60% by volume or less in an organic solvent constituting the electrolytic solution.
[0016]
In the non-aqueous electrolyte secondary battery of the present invention, the chain carboxylate may be contained in an amount of 0.01% by volume or more and 60% by volume or less in an organic solvent constituting the electrolytic solution. .
[0017]
By doing so, a decrease in the dielectric constant of the solvent constituting the electrolytic solution is suppressed, so that the cycle characteristics can be reliably improved.
[0018]
According to the present invention, there is provided an electrolyte solution for a secondary battery comprising an electrolyte and a halogen-substituted carbonate, wherein the main skeleton carbon of the halogen-substituted carbonate is saturated.
[0019]
Further, according to the present invention, there is provided a secondary battery including a cathode active material having an average discharge potential of 4.5 V or more with respect to Li metal, and an electrolyte, wherein the electrolyte includes a halogen-substituted carbonate. And a non-aqueous electrolyte secondary battery characterized in that the main skeleton carbon of the halogen-substituted carbonate is saturated.
[0020]
In the present invention, since the halogen-substituted carbonate is contained in the organic solvent constituting the electrolytic solution, the capacity deterioration of the secondary battery can be suppressed. The reason for this is that since the halogen-substituted carbonate is selectively reduced, a coating having high electric conductivity is formed on the negative electrode, so that deposition of decomposition products on the negative electrode is suppressed. It is inferred.
[0021]
In the electrolytic solution for a secondary battery according to the present invention, the halogen-substituted carbonate may be any of halogen-substituted diethyl carbonate, ethylene carbonate, or propion carbonate.
[0022]
In the non-aqueous electrolyte secondary battery of the present invention, the halogen-substituted carbonate may be any one of diethyl carbonate, ethylene carbonate, and propion carbonate.
[0023]
By doing so, the cycle characteristics of the secondary battery can be reliably improved.
[0024]
The electrolyte solution for a secondary battery of the present invention may further include a carboxylic acid ester. In the non-aqueous electrolyte secondary battery of the present invention, the electrolyte may further include a carboxylic acid ester. By doing so, a synergistic effect between the halogen-substituted carbonate and the carboxylate is exhibited, and the cycle characteristics can be dramatically improved. In this case, the type of the carboxylic acid ester is not particularly limited.
[0025]
The electrolyte solution for a secondary battery of the present invention may further include a chain carbonate or a cyclic carbonate. Further, in the nonaqueous electrolyte secondary battery of the present invention, the electrolyte may further include a chain carbonate or a cyclic carbonate. This makes it possible to adjust the dielectric constant or viscosity of the electrolytic solution.
[0026]
In the electrolytic solution for a secondary battery of the present invention, the halogen-substituted carbonate may be contained in an amount of 0.01% by volume or more and 20% by volume or less in an organic solvent constituting the electrolytic solution. Further, in the nonaqueous electrolyte secondary battery of the present invention, the halogen-substituted carbonate may be contained in an amount of 0.01% by volume or more and 20% by volume or less in the organic solvent constituting the electrolytic solution. By doing so, the increase in the viscosity of the electrolytic solution is suitably suppressed, so that the cycle characteristics can be reliably improved.
[0027]
In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode active material may be configured to include a spinel-type lithium manganese composite oxide represented by the following general formula (1).
Li_a(Ni_xMn_2-x-y-zM_yA_z) (O_4-wZ_w(1)
(However, in the general formula (1), 0.4 ≦ x ≦ 0.6, 0 ≦ y, 0 ≦ z, x + y + z <2, 0 <a <1.2, 0 <w <1, and M Is at least one selected from the group consisting of Be, Ge, B, Na, Mg, Al, K, and Ca, A is at least one of Ti or Si, and Z is at least one of F or Cl. is there.)
[0028]
By doing so, the cycle characteristics can be reliably improved. The reason for this is that the use of the element-substituted compound of the above general formula (1) as the positive electrode active material reduced the active interface of the positive electrode and suppressed the decomposition of the electrolyte between the positive electrode and the electrolyte. Inferred.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the secondary battery according to the present invention will be described. The electrolyte used for the secondary battery according to the present embodiment includes an organic solvent and a lithium salt dissolved in the organic solvent. The organic solvent contains at least one of a halogen-substituted carbonate ester and a chain carboxylate ester whose main skeleton carbon is saturated.
[0030]
As the chain carboxylic acid ester, for example, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate and the like are suitably used. Particularly, use of methyl propionate or ethyl propionate is preferable because excellent cycle characteristics can be obtained. It is preferable to add these chain carboxylic acid esters at a concentration of 0.01% by volume or more and 60% by volume or less in the organic solvent constituting the electrolytic solution. By adding 0.01% by volume or more, decomposition of the electrolytic solution can be suitably suppressed, and the cycle characteristics can be improved. Further, by adding 60% by volume or less, the dielectric constant of the electrolytic solution can be increased. it can. Further, more preferably, the content can be 0.1% by volume or more and 20% by volume or less. This makes it possible to more reliably improve the cycle characteristics.
[0031]
As the chain carboxylic acid ester, methyl butyrate, ethyl butyrate, methyl valerate, ethyl valerate and the like are also preferably used. Among them, it is particularly preferable to use methyl butyrate because excellent cycle characteristics can be obtained. In this case, the chain carboxylic acid ester is preferably added at a concentration of 0.01% by volume or more and 60% by volume or less in the organic solvent constituting the electrolytic solution. By adding 0.01% by volume or more, decomposition of the electrolytic solution can be suitably suppressed, and the cycle characteristics can be improved. Further, by adding 60% by volume or less, the dielectric constant of the electrolytic solution can be increased. it can. More preferably, it can be added in an amount of 30% by volume or more and 50% by volume or less.
[0032]
Further, examples of the halogen-substituted carbonate having a saturated main skeleton carbon include, for example, fluorine-substituted, chlorine-substituted, bromine-substituted or iodine-substituted various chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate. Products, fluorine-substituted, chlorine-substituted, bromine-substituted or iodine-substituted products of various cyclic carbonates such as ethylene carbonate and propylene carbonate. Among them, the use of a fluorine-substituted product is preferable because the cycle characteristics can be surely improved.
[0033]
Specific examples of the fluorine-substituted carbonic acid ester in which the main skeleton carbon is saturated include monofluorodimethyl carbonate, monofluoromethylethyl carbonate, difluorodimethyl carbonate, trifluoropropion carbonate, difluoroethylene carbonate, and monofluoroethylene carbonate. It is possible. Further, among them, for example, excellent cycle characteristics can be obtained by using a fluorine-substituted product of diethyl carbonate or ethylene carbonate or propion carbonate or a derivative thereof, and an increase in the viscosity of the electrolyte can be suitably suppressed. preferable.
[0034]
The amount of the fluorine-substituted carbonic acid ester in which the main skeleton carbon is saturated can be set to 0.01% by volume or more and 20% by volume or less in the organic solvent constituting the electrolytic solution. When the content is 0.01% by volume or more, the cycle characteristics are surely improved. This is presumed to be due to the reduction of the fluorine-substituted carbonate to form a highly conductive film on the negative electrode surface. Further, by setting the content to 20% by volume or less, an increase in the viscosity of the electrolytic solution can be suppressed. More preferably, the content can be set to 1% by volume or more and 10% by volume or less in the organic solvent constituting the electrolytic solution.
[0035]
Further, in addition to the halogen-substituted carbonate in which the main skeleton carbon is saturated, a carboxylate may be further contained as an electrolyte solution component. By doing so, the synergistic effect between the halogen-substituted carbonate ester having a saturated main skeleton carbon and the carboxylic acid ester further improves the cycle characteristics of the secondary battery. The type of the carboxylic acid ester is not particularly limited, and various chain carboxylic esters or various cyclic carboxylic esters can be used. For example, the above-mentioned compounds can be used.
[0036]
In addition, in addition to the above-mentioned chain carboxylic acid ester or the halogen-substituted carbonate ester whose main skeleton carbon is saturated, the electrolyte solution according to the present embodiment further includes propylene carbonate (PC), ethylene carbonate (EC), and the like. A cyclic carbonate may be included. This increases the dielectric constant of the solvent. Further, a chain carbonate such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) may be contained. In this case, the viscosity of the electrolytic solution can be reduced.
[0037]
In addition, other non-aqueous solvents can be used in the electrolytic solution together with the above-mentioned chain carboxylic acid ester or the halogen-substituted carbonate ester in which the main skeleton carbon is saturated. The other non-aqueous solvent is not particularly limited, and may be γ-lactones such as γ-butyrolactone, 1,2-methoxyethane (DME) 1, 2-ethoxyethane (DEE), ethoxymethoxyethane ( Chain ethers such as EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, acetamide, dimethylformamide, dioxolan, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, Triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative And those used as conventional solvents for nonaqueous electrolytes such as ethyl ether, 1,3-propane sultone, aniline, anisole, N-methylpyrrolidone, and alkylenebiscarbonates.
[0038]
Lithium salts dissolved in these organic solvents include, for example, LiPF₆, LiAsF₆, LiAlCl₄, LiClO₄, LiBF₄, LiSbF₆, LiCF₃SO₃, LiC₄F₉CO₃, LiC (CF₃SO₂)₂, LiN (CF₃SO₂)₂, LiN (C₂F₅SO₂)₂, LiB₁₀Cl₁₀, Lithium lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate, LiCl, LiBr, LiI, LiSCN, LiCl, imides and the like. Further, a polymer electrolyte may be used. The electrolyte concentration is, for example, 0.5 mol / l to 1.5 mol / l. If the concentration is too high, the density and the viscosity increase, and if the concentration is too low, the electric conductivity decreases.
[0039]
The electrolytic solution according to the present embodiment can be suitably used for a secondary battery provided as a positive electrode active material having an average discharge potential of 4.5 V or more with respect to Li metal. In a battery having a discharge potential of 4.5 V or higher, the electrolyte is kept under a high voltage for a long time, and the decomposition reaction of the electrolyte is accelerated. Therefore, the capacity deterioration accompanying the decomposition of the electrolyte is particularly remarkable. By using the electrolytic solution according to the present embodiment, decomposition of the electrolytic solution is suitably suppressed, and cycle characteristics are improved.
[0040]
Examples of the positive electrode active material having an average discharge potential of 4.5 V or more with respect to Li metal include LiNi._0.5Mn_1.5O₄, LiCoMnO₄, LiCrMnO₄, LiCu_0.5Mn_0.5O₄, LiFe_0.5Mn_1.5O₄, LiNiVO₄, LiCoPO₄, LiM_xMn_2-xO₄(However, M is at least one of Ni, Co, C, and Li).
[0041]
Of these, LiNi_xMn_2-xO₄It is preferable to use (0.4 <x <0.6) because a high capacity of 130 mAh / g or more can be obtained. By setting the composition of Ni, that is, the value of x to 0.4 or more, a 5 V discharge region is suitably secured, and the energy density can be increased. Further, by setting the value of x to 0.6 or less, a decrease in capacity is suppressed. Preferably, the composition of Ni, that is, the value of x is around 0.5. LiNi_xMn_2-xO₄(X = 0.5) indicates that there is a charge / discharge region for inserting and extracting Li between 4.5 V and 4.8 V with respect to Li, and a discharge region of 4.5 V or more has a charge / discharge region of 110 mAh / g or more. Very high capacity.
[0042]
As a result of further study, it was found that cycle characteristics could be improved by using a spinel-type lithium manganese composite oxide represented by the following general formula (1) as a positive electrode active material. It is considered that the reason for this is that the active interface of the positive electrode was reduced by the element replacement, and the decomposition of the electrolytic solution between the positive electrode and the electrolytic solution was suppressed.
Li_a(Ni_xMn_2-x-y-zM_yA_z) (O_4-wZ_w(1)
(However, in the general formula (1), 0.4 ≦ x ≦ 0.6, 0 ≦ y, 0 ≦ z, x + y + z <2, 0 <a <1.2, 0 <w <1, and M Is at least one selected from the group consisting of Be, Ge, B, Na, Mg, Al, K, and Ca, A is at least one of Ti or Si, and Z is at least one of F or Cl. is there.)
[0043]
The secondary battery according to the present embodiment has a positive electrode using a lithium-containing metal composite oxide as a positive electrode active material, and a negative electrode having a negative electrode active material capable of inserting and extracting lithium as a main component. A separator that does not cause a connection is sandwiched, and the positive electrode and the negative electrode are in a state of being immersed in a lithium ion conductive electrolyte, which is sealed in a battery case. When a voltage is applied to the positive electrode and the negative electrode, lithium ions are released from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material, so that the battery is charged. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the battery, lithium ions are released from the negative electrode active material, and the lithium ions are occluded in the positive electrode active material, thereby causing discharge, as opposed to charging.
[0044]
The secondary battery according to the present embodiment has, for example, a structure as shown in FIG. The positive electrode active material layer 1 is formed on the positive electrode current collector 3 to constitute a positive electrode. Further, the negative electrode active material layer 2 is formed on the negative electrode current collector 4 to constitute a negative electrode. These positive electrode and negative electrode are arranged to face each other with the porous separator 5 immersed in the electrolytic solution interposed therebetween. A positive electrode outer can 6 that houses a positive electrode and a negative electrode outer can 7 that houses a negative electrode are joined via an insulating packing portion 8.
[0045]
Next, a method for manufacturing the secondary battery in FIG. 1 will be described.
[0046]
First, a method for producing a positive electrode active material is as follows. As a raw material for producing a positive electrode active material, Li raw material is Li₂CO₃, LiOH, Li₂O, Li₂SO₄Can be used, but Li₂CO₃, LiOH and the like are suitable. Mn raw materials include electrolytic manganese dioxide (EMD), Mn₂O₃, Mn₃O₄Mn oxides such as, CMD, etc., MnCO₃, MnSO₄Etc. can be used. Ni raw materials include NiO, Ni (OH)₂, NiSO₄, Ni (NO₃)₂Etc. can be used. Oxides, carbonates, hydroxides, sulfides, nitrates and the like of the substitution element are used as the raw material of the substitution element. In the case of the Ni raw material, the Mn raw material, and the substitution element raw material, element diffusion may not easily occur during firing, and after the raw material firing, the Ni oxide, the Mn oxide, and the substitution element oxide may remain as a different phase. . For this reason, a Ni raw material, a Mn raw material, and a substitution element raw material are dissolved and mixed in an aqueous solution, and then a Ni, Mn mixture or Ni containing a substitution element precipitated in the form of a hydroxide, a sulfate, a carbonate, a nitrate, or the like. , Mn mixture can be used as a raw material. Further, it is also possible to use Ni, Mn oxide, Ni, Mn, or a substitution element mixed oxide obtained by firing such a mixture. When such a mixture is used as a raw material, Mn, Ni, and the substituting element are well diffused at the atomic level, and it becomes easy to introduce Ni and the substituting element into the 16d site of the spinel structure.
[0047]
Further, as a halogen raw material of the positive electrode active material, a halide such as LiF or LiCl is used.
[0048]
These raw materials are weighed and mixed so as to have a target metal composition ratio. The mixing is pulverized and mixed by a ball mill or the like. The mixed powder is fired at a temperature of 600 ° C. to 1000 ° C. in air or oxygen to obtain a positive electrode active material. It is desirable that the firing temperature be high in order to diffuse each element. However, if the firing temperature is too high, oxygen deficiency occurs, which adversely affects battery characteristics. For this reason, it is desirable that the temperature is about 500 ° C. to 800 ° C. in the final firing step.
[0049]
The specific surface area of the obtained lithium metal composite oxide is 3 m²/ G or less, preferably 1 m²/ G or less. This is because the larger the specific surface area, the more binder is required, which is disadvantageous in terms of the capacity density of the positive electrode.
[0050]
The obtained positive electrode active material is mixed with a conductivity-imparting agent, and formed on a current collector with a binder. Examples of the conductivity-imparting agent include a carbon material, a metal substance such as Al, and a powder of a conductive oxide. Polyvinylidene fluoride or the like is used as the binder. As the current collector, a metal thin film mainly composed of Al or the like is used.
[0051]
Preferably, the added amount of the conductivity-imparting agent is about 1 to 10% by weight, and the added amount of the binder is also about 1 to 10% by weight. This is because the larger the proportion of the active material weight, the larger the capacity per weight. If the ratio between the conductivity-imparting agent and the binder is too small, the conductivity may not be maintained or a problem of electrode peeling may occur.
[0052]
The negative electrode active material is not particularly limited as long as it can occlude lithium ions during charging and release lithium ions during discharging, and can use a material having a known material configuration. Specific examples of the substance capable of electrochemically occluding and releasing lithium ions include carbon materials such as graphite and coke;
Lithium metal or an alloy thereof, such as lithium metal, lithium-aluminum alloy, lithium-lead alloy, lithium-tin alloy;
SnO₂, SnO, TiO₂, Nb₂O₃A metal oxide whose potential is lower than that of the positive electrode active material;
And the like.
[0053]
The negative electrode active material is preferably provided on the current collector surface together with the conductive material and the adhesive. This configuration can be obtained, for example, by applying a mixture obtained by mixing a negative electrode active material, a conductive material, and an adhesive on a current collector. As the conductivity-imparting agent, for example, a carbon material or a powder of a conductive oxide can be used. Polyvinylidene fluoride or the like is used as the binder. As the current collector, a metal thin film mainly composed of Cu or the like is used.
[0054]
The secondary battery according to the present embodiment, in a dry air or an inert gas atmosphere, the negative electrode and the positive electrode are laminated via a separator, or after the laminated product is wound, or housed in a battery can, or a synthetic resin. It can be manufactured by sealing with a flexible film or the like made of a laminate with a metal foil.
[0055]
The present invention has been described based on the embodiments. These embodiments are exemplifications, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. is there.
[0056]
For example, the secondary battery shown in FIG. 1 is in the form of a coin-type cell, but the shape of the battery is not limited. A positive electrode and a negative electrode opposed to each other with a separator interposed therebetween can be in a wound type, a laminated type, or the like, and a coin type, a laminate pack, a square type cell, or a cylindrical type cell can be used as the cell.
[0057]
【Example】
(Example 1)
First, a positive electrode active material was produced as follows. Raw material MnO₂, NiO, and Li₂CO₃Was weighed so as to have a target metal composition ratio, and pulverized and mixed. The powder after mixing the raw materials is fired at 750 ° C. for 8 hours to obtain LiNi._0.5Mn_1.5O₄, Got. It was confirmed that the spinel structure had almost a single phase.
[0058]
Then, the prepared positive electrode active material and carbon as a conductivity-imparting agent were mixed, and dispersed in a solution of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone to form a slurry. The weight ratio of the positive electrode active material, the conductivity-imparting agent, and the binder was 88/6/6. The slurry was applied on the Al current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle having a diameter of 12 mm. After that, 3t / cm²And press molded.
[0059]
Using natural graphite as the negative electrode active material, carbon as a conductivity-imparting agent was mixed, and the mixture was dispersed in a solution of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone to form a slurry. The weight ratio of the negative electrode active material, the conductivity-imparting agent, and the binder was 91/1/8. The slurry was applied on the Cu current collector. Then, it was dried in vacuum for 12 hours to obtain an electrode material. The electrode material was cut into a circle having a diameter of 13 mm. Then 1t / cm²And press molded.
[0060]
A PP film was used as the separator. The positive electrode and the negative electrode were opposed to each other with no electrical contact with a separator interposed therebetween, placed in a coin cell, filled with an electrolyte, and sealed.
[0061]
As the electrolytic solution, a solvent obtained by mixing ethylene carbonate (EC), methyl propionate (MP), and dimethyl carbonate (DMC) at a ratio of 30:10:60 (vol.%) Was used as a solvent.₆Was dissolved in 1M and used.
[0062]
(Example 2)
A method similar to that of Example 1 except that a solvent obtained by mixing ethylene carbonate (EC), ethyl propionate (EP), and diethyl carbonate (DEC) at a ratio of 40: 5: 55 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Example 2 was obtained.
[0063]
(Example 3)
A method similar to that of Example 1 was used except that a solvent in which ethylene carbonate (EC), methyl acetate (MA), and diethyl carbonate (DEC) were mixed at a ratio of 50: 1: 49 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Example 3 was obtained.
[0064]
(Example 4)
A method similar to that of Example 1 except that a solvent obtained by mixing ethylene carbonate (EC), ethyl acetate (EA), and dimer carbonate (DMC) at a ratio of 40:20:40 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Example 4 was obtained.
[0065]
(Example 5)
The same method as in Example 1 was used except that a solvent in which ethylene carbonate (EC), methyl butyrate (MB), and diethyl carbonate (DEC) were mixed at a ratio of 50: 45: 5 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Example 5 was obtained.
[0066]
(Example 6)
A method similar to that of Example 1 was used except that a solvent in which ethylene carbonate (EC) and methyl butyrate (MB) diethyl carbonate (DMC) were mixed at a ratio of 40:40:20 (vol.%) Was used as a solvent for the electrolytic solution. A secondary battery of Example 6 was obtained.
[0067]
(Example 7)
Same as Example 1 except that a solvent obtained by mixing ethylene carbonate (EC), monofluorodimethyl carbonate (FDMC), and dimethyl carbonate (DMC) at a ratio of 50: 1: 49 (vol.%) Was used as a solvent for the electrolytic solution. The secondary battery of Example 7 was obtained by the method.
[0068]
(Example 8)
The same as Example 1 except that a solvent obtained by mixing ethylene carbonate (EC), monofluoroethylene carbonate (FEC), and dimethyl carbonate (DMC) at 45: 5: 50 (vol.%) Was used as a solvent for the electrolytic solution. The secondary battery of Example 8 was obtained by the method.
[0069]
(Example 9)
As a solvent for the electrolytic solution, a solvent obtained by mixing ethylene carbonate (EC), diethyl carbonate (DEC), methyl propionate (MP), and monofluoroethylene carbonate (FEC) at 29: 50: 10: 1 (vol.%) Is used. A secondary battery of Example 9 was obtained in the same manner as in Example 1 except for the difference.
[0070]
(Example 10)
As a solvent for the electrolytic solution, a solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl propionate (EP), and monofluorodimethyl carbonate (FDMC) in a ratio of 50: 39: 10: 1 (vol.%) Is used. A secondary battery of Example 10 was obtained in the same manner as in Example 1 except for the difference.
[0071]
(Comparative Example 1)
The secondary battery of Comparative Example 1 was manufactured in the same manner as in Example 1, except that a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a ratio of 50:50 (vol.%) Was used as a solvent for the electrolytic solution. Got.
[0072]
(Comparative Example 2)
The secondary battery of Comparative Example 2 was manufactured in the same manner as in Example 1 except that a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a ratio of 40:60 (vol.%) Was used as a solvent for the electrolytic solution. Got.
[0073]
(Comparative Example 3)
Raw material MnO₂, Li₂CO₃Was weighed so as to have a target metal composition ratio, and pulverized and mixed. The powder after mixing the raw materials is fired at 700 ° C. for 8 hours to obtain LiMn.₂O₄Got. It was confirmed that the spinel structure had almost a single phase.
[0074]
LiMn obtained₂O₄Was used as a positive electrode active material, and a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a ratio of 30:70 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Comparative Example 3 was obtained.
[0075]
(Comparative Example 4)
The same method as in Comparative Example 3 was used except that a solvent mixed with ethylene carbonate (EC), methyl propionate (MP), and dimethyl carbonate (DMC) 30:30:40 (vol.%) Was used as a solvent for the electrolytic solution. Thus, a secondary battery of Comparative Example 4 was obtained.
[0076]
(Comparative Example 5)
As a solvent for the electrolytic solution, a solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), monofluoroethylene carbonate (FEC), and methyl propionate (MP) at 54: 40: 1: 5 (vol.%) Is used. A secondary battery of Comparative Example 5 was obtained in the same manner as in Comparative Example 3 except for the above.
[0077]
(Comparative Evaluation Example 1)
The charge / discharge cycle characteristics of the battery manufactured as described above were evaluated. At the time of evaluation, Examples 1 to 10 and Comparative Examples 1 and 2 were charged up to 4.8 V at a charge rate of 1 C, and discharged to 3 V at a rate of 1 C. In Comparative Examples 3 to 5, charging was performed up to 4.2 V at a charging rate of 1 C, and discharging was performed up to 3 V at a rate of 1 C. Table 1 shows the results.
[0078]
[Table 1]

[0079]
As is clear from Table 1, a positive electrode active material that absorbs and releases Li at 4.5 V or more is used, and a fluorinated carbonic acid ester or a chain carboxylic acid ester whose main skeleton carbon is saturated is used as a solvent for the electrolytic solution. As a result, it was confirmed that the cycle characteristics were improved.
[0080]
【The invention's effect】
As described above, according to the present invention, a halogen-substituted carbonate or a chain carboxylate in which a main skeleton carbon is saturated in an electrolytic solution, using a positive electrode active material that absorbs and releases Li at 4.5 V or more. By containing, the reduction in capacity due to the cycle of the nonaqueous electrolyte secondary battery and the reduction in reliability at high temperatures are suppressed. Further, according to the present invention, the operating voltage of the non-aqueous electrolyte secondary battery is improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment.
[Explanation of symbols]
1 positive electrode active material layer
2 Negative electrode active material layer
3 positive electrode current collector
4 Negative electrode current collector
5 Porous separator
6 Positive outer can
7 Negative exterior can
8 Insulation packing part

Claims (15)

An electrolyte solution for a secondary battery, comprising an electrolyte and a chain carboxylic acid ester. 2. The electrolyte solution for a secondary battery according to claim 1, wherein the chain carboxylic acid ester is contained in an amount of 0.01% by volume or more and 60% by volume or less in an organic solvent constituting the electrolytic solution. Electrolyte for secondary battery. An electrolyte solution for a secondary battery, comprising an electrolyte and a halogen-substituted carbonate, wherein the main skeleton carbon of the halogen-substituted carbonate is saturated. 4. The electrolyte for a secondary battery according to claim 3, wherein the halogen-substituted carbonate is any one of diethyl carbonate, ethylene carbonate, and propion carbonate. 5. . The electrolyte solution for a secondary battery according to claim 3, further comprising a carboxylic acid ester. The electrolyte solution for a secondary battery according to any one of claims 1 to 5, further comprising a chain carbonate or a cyclic carbonate. The electrolyte solution for a secondary battery according to claim 3, wherein the halogen-substituted carbonate is contained in an amount of 0.01% by volume to 20% by volume in an organic solvent constituting the electrolytic solution. Electrolyte for a secondary battery. A secondary battery comprising: a cathode active material having an average discharge potential of 4.5 V or more with respect to Li metal; and an electrolyte, wherein the electrolyte contains an electrolyte and a chain carboxylate. Non-aqueous electrolyte secondary battery. 9. The non-aqueous electrolyte secondary battery according to claim 8, wherein the chain carboxylate is contained in an amount of 0.01% by volume or more and 60% by volume or less in an organic solvent constituting the electrolyte. Non-aqueous electrolyte secondary battery. A secondary battery comprising: a positive electrode active material having an average discharge potential of 4.5 V or more with respect to Li metal; and an electrolyte, wherein the electrolyte contains a halogen-substituted carbonate, and A non-aqueous electrolyte secondary battery characterized in that skeleton carbon is saturated. The non-aqueous electrolyte secondary battery according to claim 10, wherein the halogen-substituted carbonate is any one of diethyl carbonate, ethylene carbonate, and propion carbonate. Next battery. The non-aqueous electrolyte secondary battery according to claim 10, wherein the electrolyte further includes a carboxylic acid ester. The non-aqueous electrolyte secondary battery according to any one of claims 10 to 12, wherein the electrolyte further comprises a chain carbonate or a cyclic carbonate. 14. The non-aqueous electrolyte secondary battery according to claim 10, wherein the halogen-substituted carbonate is contained in an amount of 0.01% by volume or more and 20% by volume or less in an organic solvent constituting the electrolytic solution. Characteristic non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery according to any one of claims 8 to 14, wherein the positive electrode active material includes a spinel-type lithium manganese composite oxide represented by the following general formula (1). Electrolyte secondary battery.
_{Li a (Ni x Mn 2-} x-y-z M y A z) (O 4-w Z w) (1)
(However, in the general formula (1), 0.4 ≦ x ≦ 0.6, 0 ≦ y, 0 ≦ z, x + y + z <2, 0 <a <1.2, 0 <w <1, and M Is at least one selected from the group consisting of Be, Ge, B, Na, Mg, Al, K, and Ca, A is at least one of Ti or Si, and Z is at least one of F or Cl. is there.)

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