JP6910595B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

Conventionally, as a positive electrode active material for a non-aqueous electrolyte secondary battery represented by a lithium secondary battery, _{a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure has been studied, and LiCoO ₂ and LiNi _1/2 Mn _{1 have been studied.} The molar ratio of Mn in the transition metal (Me) constituting the lithium transition metal composite oxide, such as _{/ 2} O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O _{2, is 0.} Non-aqueous electrolyte secondary batteries using a so-called "LiMeO _{type 2" active material having a value of 5 or less have been put into practical use.} Further, the molar ratio Mn / Me of Mn in the transition metal (Me) constituting the lithium transition metal composite oxide exceeds 0.5, and the molar ratio Li / Me of lithium (Li) to Me is larger than 1. So-called "lithium-rich" active materials are also being studied.

The capacity and charge / discharge cycle performance of a battery using these lithium transition metal composite oxides as the positive electrode active material are affected by the powder characteristics of the active material as well as the types and compositions of the elements constituting the transition metal. It is known.
In general, it is known that when the sintering reaction proceeds sufficiently in the step of synthesizing a lithium transition metal composite oxide, the porosity of the particles tends to decrease. As a method for sufficiently advancing the sintering reaction, a method of raising the firing temperature and a method of mixing LiF as a sintering aid are known (see, for example, Non-Patent Documents 1 to 3).

On the other hand, as a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery, a mixed solvent of a cyclic carbonate having a high dielectric constant and a chain carbonate having a low viscosity is generally used. Chain carbonates such as dimethyl carbonate (hereinafter referred to as "DMC") are known to affect low temperature performance (see, for example, Patent Documents 1 to 3).

Patent Document 1 describes a cylindrical non-aqueous electrolyte secondary battery having a positive electrode containing a lithium transition metal composite oxide, a negative electrode, a separator, and an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent. The energy density is 550 Wh / L or more, the mass of the electrolytic solution is 55% or less with respect to the mass of the lithium transition metal composite oxide, the electrolytic solution contains dimethyl carbonate, and the volume ratio of the dimethyl carbonate. There more than 20% relative to the total amount of the nonaqueous solvent is 55% or less, the lithium transition metal composite oxide has the general _{formula: Li x Ni 1- (p +} q + r) Co p Al q MrO 2 + y (M is tungsten , At least one element selected from the group consisting of titanium and zirconium, 0.9 ≦ x ≦ 1.2, −1.0 ≦ y ≦ 0.1, 0.0001 ≦ r ≦ 0.01, 0 < A cylindrical non-aqueous electrolyte secondary battery represented by p + q + r ≦ 0.4) ”(claim 1).

Then, Patent Document 1 states, "In the present invention, by reducing the volume ratio of dimethyl carbonate in the electrolytic solution to 55% or less with respect to the total amount of the non-aqueous solvent, the freezing point of the electrolytic solution becomes −30 ° C. or less. The discharge characteristics in a low temperature environment are improved. Further, by using a lithium transition metal composite oxide in which at least one element selected from the group consisting of tungsten, titanium, and zirconium is added to the positive electrode active material, the positive electrode active material is used. The reaction uniformity of the lithium transition metal composite oxide is improved. As a result, the uniformity of the concentration distribution of the electrolytic solution in the electrode plate is improved, and the precipitation of lithium metal on the negative electrode due to the withering of the electrolytic solution is suppressed. Cycle characteristics are improved. ”(Paragraphs [0014], [0015]).

Patent Document 2 includes "a positive electrode containing a lithium-containing composite oxide, a negative electrode containing a carbon material capable of occlusion and release of lithium, and a non-aqueous electrolyte, and the carbon material is a graphitizable carbon material. In the wide-angle X-ray diffraction pattern of the graphitizable carbon material, which includes and is measured using CuKα rays, the peak attributed to the (100) plane of the peak intensity I (101) attributable to the (101) plane. The ratio to the intensity I (100) is as follows:
0.5 ≤ I (101) / I (100) ≤ 0.7
The c-axis direction crystallite thickness Lc (004) of the easily graphitizable carbon material is 20 nm or more and 60 nm or less, and the non-aqueous electrolyte is a solute dissolved in a non-aqueous solvent and the non-aqueous solvent. The non-aqueous solvent contains propylene carbonate, ethylene carbonate, and at least one chain carbonate selected from dimethyl carbonate and ethyl methyl carbonate, and the propylene carbonate and the ethylene carbonate are the same. The chain carbonate accounts for 40% by volume or more and 80% by volume or less of the non-aqueous solvent, and the chain carbonate accounts for 20% by volume or more and 60% by volume or less of the non-aqueous solvent, and accounts for the total of the propylene carbonate and the ethylene carbonate. A non-aqueous electrolyte secondary battery in which the proportion of propylene carbonate is 60% by volume or more and 90% by volume or less. "(Claim 1) is described.

Further, Patent Document 2 states that "a lithium-containing composite oxide is used as the positive electrode active material. Examples of the lithium-containing composite oxide include LiCoO ₂ , LiNiO _{2 , and LiMn 2} O ₄ having a spinel structure. Further, in order to improve the cycle life characteristics, a part of the transition metal contained in the lithium-containing composite oxide may be replaced with another element. For example, a part of the Ni element may be replaced with Co or another element. _{LiNiO 2} substituted with (Al, Mn, Ti, etc.) can be used as the positive electrode active material. ”(Paragraph [0021]),“ In the present invention, the non-aqueous solvent is dimethyl carbonate in addition to PC and EC. It contains a chain carbonate such as (DMC) and ethyl methyl carbonate (EMC). At this time, the ratio of the chain carbonate to the non-aqueous solvent is preferably 20% by volume to 60% by volume. By further containing the chain carbonate in the non-aqueous solvent, the viscosity of the electrolytic solution can be lowered, so that the low temperature characteristics and the output characteristics can be further improved. ”(Paragraph [0031]). There is.

Patent Document 3 states that "at least one type of solvent selected from diethyl carbonate and ethyl methyl carbonate is 40% by volume to 50% by volume, ethylene carbonate is 4% by volume to 10% by volume, and propylene carbonate is 10% by volume to 17% by volume. A lithium ion secondary battery characterized by being a mixed solvent of 30% by volume and 30% by volume to 40% by volume of dimethyl carbonate. ”(Claim 1) is described.

Then, "In the present invention, as the positive electrode active material, a material conventionally used in a lithium ion secondary battery can be used, for example, the Li-transition represented by the following general formula (1) or (2). A metal composite oxide is exemplified.
Li _A M _1-X Me _x O ₂ (1)
Li _A M _2-x Me _x O ₄ (2)
In formula (1), M represents a transition metal such as Co, Ni, Mn, V, Ge. In formula (2), M represents a transition metal such as Mn, Fe, Ni or the like. In formulas (1) and (2), Me is a Group 3-10 element in the periodicity table, such as Zr, V, Cr, Mo, Fe, Co, Mn, Ni, or a Group 13-15 element, such as B. , Al, Ge, Pb, Sn, Sb and the like. However, as Me, an element different from the element selected as M is selected. Of these, LiCoO ₂ is particularly preferred in the present invention. (Paragraphs [0029] to [0031]), "If an electrolytic solution whose viscosity does not increase at low temperature is used, the electrolytic solution can be permeated into the electrode at low temperature without lowering the density of the active material." Therefore, it is considered that the low temperature characteristics can be improved. However, in the conventional electrolytic solution, there is a problem that the freezing point is rather increased when trying to lower the viscosity. For example, the electrolytic solution has a problem as compared with the conventional one. Of the components to be blended, dimethyl carbonate has the effect of lowering the viscosity of the electrolytic solution by increasing the blending ratio, but conversely raises the freezing point of the electrolytic solution. ”(Paragraph [0007]). ing.

JP-A-2015-162406 Japanese Patent No. 4994628 Japanese Unexamined Patent Publication No. 2001-52682

J. Electrochem. Soc., Jouanneau et al, 151, 1749 (2004) J. Electrochem. Soc., Kim et al, 152, 1707 (2005) J. Electrochem. Soc., Kim et al, 154, 561 (2007)

As described in Patent Documents 1 to 3, _{non-water containing a non-aqueous electrolyte in which a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure is used as a positive electrode active material and an appropriate amount of DMC is contained in the solvent. Electrolyte secondary batteries are known to have improved low temperature performance. However, when a non-aqueous electrolyte containing DMC is used, there arises a problem that the charge / discharge cycle performance is inferior. The reason can be inferred as follows. DMC has excellent reduction resistance, and the decrease in the utilization rate of the negative electrode with the progress of the charge / discharge cycle is small. If the decrease in the utilization rate of the negative electrode is small, the positive electrode is repeatedly discharged to a deep discharge depth (low SOC region). When the charge / discharge cycle to a deep discharge depth is repeated, cracks are formed in the positive electrode active material particles, which causes an increase in resistance and expansion of the electrode plate. As a result, it is presumed that the charge / discharge cycle performance deteriorates.

In view of the above problems, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent low temperature performance and charge / discharge cycle performance.

In the present invention, the following means are adopted in order to solve the above problems.
A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode has an α-NaFeO ₂ structure, and is a powder X-ray diffraction diagram using CuKα rays. the half-width of the diffraction peak at ° is .125-0.145 °, a lithium transition metal composite oxide porosity of 1.5 to 3.5% (however, "compositional formula _Li a _{Mn 0.5 -X} Ni _0.5-y M _{x + y} O ₂ (where 0 <a <1.3, -0.1 ≤ x-y ≤ 0.1, M is an element other than Li, Mn, Ni) The non-aqueous electrolyte contains a non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the volume ratio of the chain carbonate to the non-aqueous solvent is A non-aqueous electrolyte secondary battery having a volume ratio of dimethyl carbonate in the chain carbonate of 60% or more and 10% or more.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having excellent low temperature performance and excellent charge / discharge cycle performance.

Photographs of the lithium transition metal composite oxide particles according to the examples of the present invention after the charge / discharge cycle (Examples 1-4, 2-4, Reference Example 2-4). Photograph after charge / discharge cycle of particles of lithium transition metal composite oxide according to a comparative example of the present invention (Comparative Reference Example 2-3) External perspective view showing an embodiment of a non-aqueous electrolyte secondary battery according to the present invention. Schematic diagram showing a power storage device in which a plurality of non-aqueous electrolyte secondary batteries according to the present invention are assembled.

The configuration and the action and effect of the present invention will be described with technical ideas. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. It should be noted that the present invention can be practiced in various other forms without departing from its spirit or major features. Therefore, the embodiments or experimental examples described below are merely examples in all respects and should not be construed in a limited manner. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

Applicants have increased the volume per volume by using particles of a lithium transition metal composite oxide having an appropriate void ratio and a controlled crystalline α-NaFeO _{type 2 crystal structure as the positive electrode active material.} It has been found that a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be obtained as well as enhanced (Japanese Patent Application No. 2015-244008). The present invention relates to a non-aqueous electrolyte secondary battery in which a positive electrode containing this active material is combined with a non-aqueous electrolyte containing DMC in a non-aqueous solvent.

[Positive electrode active material]
The lithium transition metal composite oxide contained in the positive electrode active material of the non-aqueous electrolyte secondary battery according to one embodiment of the present invention (hereinafter referred to as “the present embodiment”) is Ni, Co as a transition metal element (Me). And Mn are preferably contained. Typically, it is represented by the composition formula Li _{1 + x} Me _1-x O ₂ (Me: a transition metal containing Ni, Co and Mn). In order to obtain a non-aqueous electrolyte secondary battery having a high energy density, it is preferable that −0.1 <x <0.1. More preferably, −0.05 ≦ x ≦ 0.09.

As an example, the lithium transition metal composite oxide according to the present embodiment is represented by the composition formula Li (Ni _a Co _b Mn _c ) O ₂ (a + b + c = 1) when x = 0.
In the present embodiment, in order to improve the charge / discharge cycle performance of the non-aqueous electrolyte secondary battery, a, that is, the molar ratio of Ni to the transition metal element Me, Ni / Me, is set to 0.3 to 0.6. Is preferable. As described above, the lithium transition metal composite oxide according to the present embodiment has a half width of the diffraction peak at 2θ: 44 ± 1 ° in the powder X-ray diffraction diagram using CuKα rays at 0.125 to 0.145 °. Yes, the porosity is 1.5-3.5%. When the lithium transition metal composite oxide has such characteristics, it has an effect of being able to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance. The above action is more effectively achieved by applying it to a lithium transition metal composite oxide having a relatively large Ni / Me molar ratio of Ni to the transition metal element Me. Therefore, Ni / Me is more preferably 0.4 to 0.6.
Further, in order to make the active material particles sufficiently conductive, b, that is, the molar ratio of Co to the transition metal element Me, Co / Me, is preferably 0 to 0.4.
Further, in order to reduce the material cost, c, that is, the molar ratio of Mn to the transition metal element Me, Mn / Me, is preferably 0.2 to 0.6, and preferably 0.2 to 0.5. Is more preferable.

Further, a small amount of other metals such as alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and transition metals typified by 3d transition metals such as Fe and Zn, as long as the effects of the present invention are not impaired. Is not excluded.

The lithium transition metal composite oxide according to this embodiment has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charging / discharging) and after charging / discharging is attributed to R3-m. In addition, "R3-m" should be originally described by adding a bar "-" on "3" of "R3m".

The lithium transition metal composite oxide according to the present embodiment is diffracted belonging to the (104) plane when the space group R3-m is used in the crystal structure model based on the X-ray diffraction (using a CuKα radiation source) pattern. The half width of the peak (diffraction peak of 2θ = 44 ± 1 °) (hereinafter referred to as “FWHM (104)”) is 0.125 to 0.145 °. By using a lithium transition metal composite oxide in which FWHM (104) is in the above specific range and the void ratio is in the range of 1.5 to 3.5% as the positive electrode active material, the charge / discharge cycle performance is excellent. A non-aqueous electrolyte secondary battery can be obtained.
When the FWHM (104) is smaller than 0.125 °, the charge / discharge cycle performance deteriorates even when the porosity is in the range of 1.5 to 3.5%. When the FWHM (104) is larger than 0.145 °, the porosity also exceeds 3.5%, and the charge / discharge cycle performance deteriorates. Even when the FWHM (104) is in the range of 0.125 to 0.145 °, if the porosity exceeds 3.5%, the charge / discharge cycle performance deteriorates.
Therefore, in the positive electrode active material according to the present embodiment, it is important that the FWHM (104) is 0.125 to 0.145 ° and the porosity is 1.5 to 3.5%.

The reason why the charge / discharge cycle performance of the non-aqueous electrolyte secondary battery is improved by setting the half width FWHM (104) and the void ratio of the lithium transition metal composite oxide according to the present embodiment within the specific ranges as described above. , Is presumed as follows.
Crystallographically, FWHM (104) is a parameter indicating three-dimensional crystallinity, and the larger the FWHM (104), the larger the lattice strain of the entire crystal. Therefore, it is considered that the fact that the FWHM (104) is 0.125 to 0.145 ° indicates that the lattice strain of the crystal is within a certain range.
Further, the porosity of 1.5 to 3.5% is considered to indicate that the pore volume inside the active material particles is within a certain range. If the porosity is less than 1.5%, the electrolytic solution does not easily penetrate into the active material particles, so that good cycle characteristics cannot be obtained. On the other hand, if the porosity exceeds 3.5%, the specific surface area of the active material particles becomes too high, so that a side reaction with the electrolytic solution during charging is particularly promoted, and good cycle characteristics cannot be obtained.
Therefore, it is presumed that the effect of excellent charge / discharge cycle performance can be achieved by setting the lattice strain of the crystal and the pore volume inside the active material particles within a certain range.

Further, it is preferable that the lithium transition metal composite oxide does not change its structure during overcharging. This can be confirmed by observing as a single phase belonging to the space group R3-m on the X-ray diffraction pattern when electrochemically oxidized to a potential of 5.0 V (vs. Li ^{/ Li +).} As a result, a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be obtained.

Further, the lithium transition metal composite oxide has an oxygen position parameter obtained from crystal structure analysis by the Rietveld method based on an X-ray diffraction pattern of 0.262 or less at the end of discharge and 0.267 or more at the end of charge. preferable. As a result, a non-aqueous electrolyte secondary battery having excellent high rate discharge performance can be obtained. The oxygen position parameter is the spatial coordinate of Me (transition metal) (0,0,0) for _{the α-NaFeO type 2} crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m. The value of z when the spatial coordinates of Li (lithium) are defined as (0, 0, 1/2) and the spatial coordinates of O (oxygen) are defined as (0, 0, z). That is, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position.

[Measurement of half width]
The crystal structure and half-price width of the lithium transition metal composite oxide are measured by powder X-ray diffraction measurement using an X-ray diffractometer. In the present specification, FWHM (104) is defined as being measured under the following conditions. The radiation source is CuKα, and the acceleration voltage and current are 30 kV and 15 mA, respectively. The sampling width is 0.01 deg, the scanning time is 14 minutes (scan speed is 5.0), the divergent slit width is 0.625 deg, the light receiving slit width is open, and the scattering slit is 8.0 mm. The obtained X-ray diffraction data is indexed on the (104) plane in the space group R3-m by using the attached software "PDXL" of the X-ray diffraction device, and 2θ = 44 ° ± 1 on the X-ray diffraction diagram. The full width at half maximum FWHM (104) for the diffraction peak present at ° is determined.

[Measurement of porosity]
In the present specification, the porosity of the lithium transition metal composite oxide is defined as being measured under the following conditions. For the measurement, "autosorb iQ" manufactured by Quantachrome and the control / analysis software "ASiQ win" are used. 1.00 g of lithium transition metal composite oxide particles are placed in a sample tube for measurement and vacuum dried at 120 ° C. for 12 hours to sufficiently remove water in the measurement sample. Next, the isotherms on the adsorption side and the desorption side are measured within a range of 0 to 1 relative pressure P / P0 (P0 = about 770 mmHg) by a nitrogen gas adsorption method using liquid nitrogen. Then, the pore distribution is evaluated by calculating by the BJH method using the isotherms on the desorption side, and the pore volume ΔV is obtained. Separately, the true density d of the particles of the lithium transition metal composite oxide is obtained by measuring the true density using helium gas using "ULTRAPYCNOMETER1000" manufactured by Quantachrome. Using these, the porosity is calculated by the following formula.
(Porosity) = ΔV / (1 / d + ΔV) × 100 “%”

[Manufacturing method of positive electrode active material]
Next, a method for producing an active material for a non-aqueous electrolyte secondary battery according to the present embodiment will be described.
The active material for a non-aqueous electrolyte secondary battery of the present invention basically contains the metal elements (Li, Ni, Co, Mn) constituting the active material according to the composition of the target active material (oxide). It can be obtained by adjusting the raw material and firing it. However, regarding the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in anticipation that a part of the Li raw material will disappear during firing.
In producing an oxide having the desired composition, the so-called "solid phase method" in which salts of Li, Ni, Co, and Mn are mixed and fired, or Ni, Co, and Mn are present in one particle in advance. A "coprecipitation method" is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and calcined with the coprecipitation precursor. In the synthesis process by the "solid phase method", it is difficult to obtain a sample in which each element is uniformly distributed in one particle, because Mn is particularly difficult to dissolve uniformly in Ni and Co. In the literature and the like, many attempts have been made to dissolve Mn in a part of Ni or Co by the solid phase method (LiNi _1-x Mn _x O ₂ etc.), but the "coprecipitation method" is selected. It is easier to obtain a uniform phase at the atomic level. Therefore, in the examples described later, the "coprecipitation method" was adopted.

In the present embodiment, it is preferable to add an aqueous solution of a raw material containing Ni, Co and Mn and co-precipitate the compound containing Ni, Co and Mn in the solution to prepare a precursor.
In producing a coprecipitated precursor, Mn among Ni, Co, and Mn is easily oxidized, and it is not easy to produce a coprecipitated precursor in which Ni, Co, and Mn are uniformly distributed in a divalent state. , Ni, Co, Mn at the atomic level tends to be inadequate. Therefore, in the present embodiment, it is preferable to remove the dissolved oxygen in order to suppress the oxidation of Mn distributed in the coprecipitation precursor. Examples of the method for removing dissolved oxygen include a method of bubbling a gas containing no oxygen. The gas containing no oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ) and the like can be used.

The pH in the step of coprecipitating a compound containing Ni, Co and Mn in a solution to prepare a precursor is not limited, but an attempt is made to prepare the coprecipitated precursor as a coprecipitated hydroxide precursor. If so, it can be 10.5 to 14. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 11.5 or less, the tap density can be set to 1.00 g / cm ³ or more, and the high rate discharge performance can be improved. Further, by setting the pH to 11.0 or less, the particle growth rate can be promoted, so that the stirring duration after the completion of dropping the raw material aqueous solution can be shortened.
Further, when the coprecipitating precursor is to be prepared as a coprecipitating carbonate precursor, it can be 7.5 to 11. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cm ³ or more, and the high rate discharge performance can be improved. Further, by setting the pH to 8.0 or less, the particle growth rate can be promoted, so that the stirring duration after the completion of dropping the raw material aqueous solution can be shortened.

The raw material of the co-precipitation precursor is nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate or the like as the Ni compound, and cobalt sulfate, cobalt nitrate, cobalt acetate or the like as the Co compound, Mn compound. Examples thereof include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, and manganese acetate.

The dropping rate of the raw material aqueous solution greatly affects the uniformity of the element distribution within one particle of the coprecipitation precursor to be produced. The preferred dropping rate is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably 30 mL / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 mL / min or less, and most preferably 5 mL / min or less.

Further, when _{a complexing agent such as NH 3} is present in the reaction vessel and certain convection conditions are applied, the particles rotate and in the stirring vessel by continuing stirring after the completion of dropping the raw material aqueous solution. Revolution is promoted, and in this process, the particles gradually grow into convective spheres while colliding with each other. That is, the coprecipitation precursor undergoes a two-step reaction of a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction vessel and a precipitation formation reaction that occurs while the metal complex is retained in the reaction vessel. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the completion of dropping of the raw material aqueous solution.

The preferable stirring duration after the completion of dropping the aqueous solution of the raw material is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery becomes insufficient due to the particle size becoming too large, 30 hours or less is preferable, 25 hours or less is more preferable, and 20 hours or less is most preferable.

In the method for producing a positive electrode active material according to the present embodiment, it is preferable that fluorine ions are present in the reaction solution when the precursor (co-precipitated precursor) is produced as described above. It is preferable that ammonium ions are further present in the reaction solution. Even in the prior art, ammonium ions are used as a neutralizing agent and a complexing agent (chelating agent), but since fluorine ions are present at the same time as ammonium ions, a high-density precursor is produced due to the effect of ammonium ions as a chelating agent. It is preferable because it can make a body. In addition, the presence of fluoride ions can allow fluorine to exist even inside the precursor. As a method for simultaneously presenting fluorine ions and ammonium ions, ammonium fluoride may be added, or ammonium chloride and sodium fluoride may be added as respective compounds. Here, it is preferable that there are not too many fluoride ions in the reaction solution. When ammonium fluoride is added, the ammonium fluoride concentration in the reaction vessel is preferably 0.1 to 0.3 mol / L. As a result, the amount of fluorine in the precursor can be made not too large, so that the possibility that the process in which lithium hydroxide melted during firing enters the precursor and diffuses can be reduced.

The active material for a non-aqueous electrolyte secondary battery according to the present embodiment can be suitably produced by mixing the coprecipitation precursor and the Li compound and then heat-treating the active material.
By combining the precursor obtained by the presence of fluorine ions in the coprecipitation reaction solution as described above with the conventional technique of firing in the presence of a sintering aid such as LiF, FWHM (104) Is 0.125 to 0.145 °, and a positive electrode active material having a porosity of 1.5 to 3.5% can be obtained, which has the effect of improving charge / discharge cycle performance. As the mechanism of action, the following inferences are possible. Simply applying a sintering aid such as LiF during firing only causes the precursor particles and the sintering aid to come into contact with each other in a solid phase, so that the sintering aid acts only on the surface of the active material particles. do not have. On the other hand, in the present embodiment, by coexisting fluorine at the stage of forming the precursor from the solution, fluorine can be present even inside the precursor particles, so that the crystal morphology tends to be rounded. An active material having a more effective sintering effect, high crystalline uniformity, and an appropriately small porosity can be obtained. Therefore, it is presumed that the side reaction with the electrolytic solution was suppressed and the charge / discharge cycle performance was improved.
It is preferable to use _{LiF, Li 2} SO ₄ or Li ₃ PO ₄ as a sintering aid together with lithium hydroxide and lithium carbonate which are usually used as Li compounds. The addition ratio of these sintering aids is preferably 1 to 10 mol% with respect to the total amount of the Li compound. It is preferable that the total amount of the Li compound is excessively charged by about 1 to 5% in anticipation that a part of the Li compound will disappear during firing.

The firing temperature affects the reversible capacity of the active material.
If the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In this embodiment, the firing temperature is preferably 900 ° C. or higher. By setting the temperature to 900 ° C. or higher, the full width at half maximum FWHM (104) of the diffraction peak of the active material can be set to 0.145 ° or lower, and the charge / discharge cycle performance can be improved.
In addition, the inventors analyzed in detail the half-value width of the diffraction peak of the active material, and found that strain remained in the lattice in the sample synthesized at a temperature lower than 750 ° C. It was confirmed that most of the distortion could be removed. The size of the crystallites increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material according to the present embodiment, good discharge capacity can be obtained by aiming for particles in which there is almost no lattice distortion in the system and the crystallite size is sufficiently grown. Specifically, it is preferable to adopt a synthesis temperature (calcination temperature) and a Li / Me ratio composition such that the amount of strain exerted on the lattice constant is 2% or less and the crystallite size grows to 50 nm or more. all right. When electrodes using these active materials are molded and charged / discharged, changes due to expansion and contraction can be seen, but it is preferable that the crystallite size is maintained at 30 nm or more even during the charging / discharging process. ..

On the other hand, if the firing temperature is too high _{, the structure changes from the layered α-NaFeO 2} ^{structure to the rock salt type cubic structure, which is disadvantageous for Li +} movement in the active material during the charge / discharge reaction, and the discharge performance deteriorates. .. In this embodiment, the firing temperature is preferably 1000 ° C. or lower. By setting the temperature to 1000 ° C. or lower, the full width at half maximum FWHM (104) of the diffraction peak of the active material according to the present embodiment can be set to 0.125 ° or more, and the charge / discharge cycle performance can be improved.
Therefore, when the positive electrode active material containing the lithium transition metal composite oxide of the present invention is produced, the firing temperature is preferably 900 to 1000 ° C. in order to improve the charge / discharge cycle performance.

[Negative electrode material]
The negative electrode material is not limited, and any material may be selected as long as it can release or occlude lithium ions. For _{example, Li [Li 1/3 Ti 5/3]} O 4 titanium-based material of lithium titanate having a spinel type crystal structure typified by, Si and Sb, the alloy material of lithium metal, such as Sn-based, lithium alloys (Lithium-metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, alloys capable of storing and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon, etc.) and the like can be mentioned.

[Positive electrode / Negative electrode]
The powder of the positive electrode active material and the powder of the negative electrode material, which are the main constituents of the positive electrode and the negative electrode, preferably have an average particle size of 100 μm or less. In particular, the powder of the positive electrode active material is preferably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. A crusher or a classifier may be used to obtain the powder in a predetermined shape. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like is used. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. The classification method is not particularly limited, and a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

In addition to the main components, the positive electrode and the negative electrode may contain a conductive agent, a binder, a thickener, a filler, and the like as other components.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance, but is usually natural graphite (scaly graphite, scaly graphite, earthy graphite, etc.), artificial graphite, carbon black, acetylene black, etc. Conductive materials such as Ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, conductive ceramic material, etc. can be contained as one kind or a mixture thereof. ..

Among these, acetylene black is desirable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by weight to 50% by weight, particularly preferably 0.5% by weight to 30% by weight, based on the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, it is possible to mix powder mixers such as V-type mixers, S-type mixers, mixers, ball mills, and planetary ball mills in a dry or wet manner.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene and polypropylene, ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM and styrene butadiene. A polymer having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

The filler is not limited as long as it is a material that does not adversely affect the battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The amount of the filler added is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

For the positive electrode and the negative electrode, the main constituents (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials are kneaded to form a mixture, which is mixed with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained mixed solution is coated on a current collector described in detail below, or crimped and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours to be suitably produced. .. Regarding the coating method, for example, it is desirable to apply the coating to an arbitrary thickness and an arbitrary shape by using a means such as a roller coating such as an applicator roll, a screen coating, a doctor blade method, a spin coating, or a bar coater. It is not limited.

As the current collector, a current collector foil such as Al foil or Cu foil can be used. Al foil is preferable as the current collecting foil of the positive electrode, and Cu foil is preferable as the current collecting foil of the negative electrode. The thickness of the current collector foil is preferably 10 to 30 μm. The thickness of the mixture layer is preferably 40 to 150 μm (excluding the thickness of the current collector foil) after pressing.

[Non-aqueous electrolyte]
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the present embodiment contains a non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the volume ratio of the chain carbonate to the non-aqueous solvent is 60% or more. There is no particular limitation as long as the volume ratio of DMC in the chain carbonate is 10% or more, and those generally proposed for use in non-aqueous electrolyte secondary batteries and the like can be used. be. Cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, fluoroethylene carbonate (FEC), chloroethylene carbonate, vinylene carbonate and the like; chain carbonates other than DMC include diethyl carbonate (DEC), Ethyl methyl carbonate (EMC) and the like can be mentioned.
Non-aqueous solvents are cyclic esters such as γ-butyrolactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or its derivatives; 1, Ethers such as 3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyetane, methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or its derivatives; ethylene sulfide, It may contain sulfolane, sulton or a derivative thereof, etc. alone or in combination of two or more.

The volume ratio of the chain carbonate to the non-aqueous solvent is preferably 60% or more, more preferably 70% or more in order to reduce the viscosity of the non-aqueous electrolyte. On the other hand, when the volume ratio exceeds 80%, the content of the cyclic carbonate having a high dielectric constant decreases, so that it is preferably 80% or less.
The volume ratio of DMC in the chain carbonate is preferably 10% or more, more preferably 30% or more, and particularly preferably 40% or more in order to improve low temperature performance.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF _{4 , LiAsF 6} , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN and other inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅₎ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C) ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearyl sulfonate, lithium octyl sulfonate, Examples thereof include organic ionic salts such as lithium dodecylbenzenesulfonate, and these ionic compounds can be used alone or in combination of two or more.

Furthermore, _{by using a mixture of LiPF 6} or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. It is more desirable because the low temperature characteristics can be further enhanced and self-discharge can be suppressed.

The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / L to 5 mol / L, more preferably 0.5 mol / L to 2 in order to surely obtain a non-aqueous electrolyte battery having high battery characteristics. It is .5 mol / L.

[Separator]
As the separator, it is preferable to use a porous membrane, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the material constituting the separator for a non-aqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, foot Vinylidene-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene Examples thereof include a copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, from the viewpoint of charge / discharge characteristics, the porosity is preferably 20% by volume or more.

Further, as the separator, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, polyvinylidene fluoride and the like and an electrolyte may be used. It is preferable to use the non-aqueous electrolyte in the gel state as described above because it has an effect of preventing liquid leakage.

Further, when the separator is used in combination with the above-mentioned porous membrane, non-woven fabric or the like and the polymer gel, it is desirable because the liquid retention property of the electrolyte is improved. That is, the pro-solvent polymer is formed by forming a film coated with a pro-solvent polymer having a thickness of several μm or less on the surface of the polyethylene micropore membrane and the micropore wall surface, and retaining the electrolyte in the micropores of the film. Gells.

Examples of the pro-solvent polymer include, in addition to polyvinylidene fluoride, a polymer in which an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a monomer having an isocyanato group or the like is crosslinked. The monomer can be subjected to a cross-linking reaction by heating or using ultraviolet rays (UV) in combination with a radical initiator, or by using active rays such as an electron beam (EB).

[Structure of non-aqueous electrolyte secondary battery]
The configuration of the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and conventionally used terminals, insulating plates, battery containers, and the like may be used as they are. Examples of the external shape include a cylindrical battery, a square (rectangular) battery, a flat battery, and the like.

FIG. 3 shows an external perspective view of a rectangular non-aqueous electrolyte secondary battery 1 according to an embodiment of the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 3, the electrode group 2 is housed in the battery container 3. The electrode group 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

[Configuration of power storage device]
The present invention can also be realized as a power storage device in which a plurality of the above-mentioned non-aqueous electrolyte secondary batteries 1 are assembled. An embodiment of the power storage device is shown in FIG. In FIG. 4, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

A non-aqueous electrolyte secondary battery according to an embodiment of the present invention is produced as shown in the following reference example, the cycle capacity retention rate is measured, and then the non-aqueous electrolyte battery according to the embodiment is produced. , Cycle capacity retention rate and low temperature performance (0 ° C / 25 ° C capacity ratio [%]) were measured.
(Reference example 1)
(Reference Example 1-1)
<Precursor preparation process>
In preparing the positive electrode active material for a non-aqueous electrolyte secondary battery, a hydroxide precursor was prepared using a reaction crystallization method. First, 350.5 g of nickel sulfate hexahydrate, 374.8 g of cobalt sulfate heptahydrate, and 321.5 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water to dissolve Ni: Co. A 1.0 mol / L sulfate aqueous solution having a Mn molar ratio of 1: 1: 1 was prepared. Next, 2 L of an aqueous solution prepared by dissolving ammonium fluoride in ion-exchanged water so as to be 0.01 mol / L was poured into a 5 L reaction vessel, and Ar gas was bubbled for 30 minutes to allow oxygen contained in the ion-exchanged water. Was removed. The temperature of the reaction vessel is set to 50 ° C. (± 2 ° C.), and the inside of the reaction vessel is stirred at a rotation speed of 1500 rpm using a paddle blade equipped with a stirring motor so that convection occurs sufficiently in the reaction layer. did. The aqueous sulfate solution was added dropwise to the reaction vessel at a rate of 3 ml / min. Here, the reaction is carried out by appropriately dropping a mixed alkaline solution consisting of 4.0 mol / L sodium hydroxide, 0.5 mol / L aqueous ammonia, and 0.5 M hydrazine from the start to the end of the dropping. The pH in the tank was controlled to always maintain 11.0 (± 0.1), and a part of the reaction solution was discharged by overflow so that the total amount of the reaction solution did not always exceed 2 L. .. After completion of the dropping, stirring in the reaction vessel was continued for another 3 hours. After the stirring was stopped, the mixture was allowed to stand at room temperature for 12 hours or more.
Next, the hydroxide precursor particles generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an agate automatic mortar for several minutes. In this way, a hydroxide precursor was prepared.

<Baking process>
To 1.898 g of the hydroxide precursor, 0.887 g of lithium hydroxide monohydrate and 0.006 g of lithium fluoride were added, mixed well using an automatic agate mortar, and Li :( Ni, Co, Mn. ): The mixed powder was prepared so that the molar ratio of F was 1: 1: 0.01. It was molded at a pressure of 6 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2 g. One of the pellets was placed on an alumina boat having a total length of about 100 mm, installed in a box-type electric furnace (model number: AMF20), and heated in an air atmosphere under normal pressure from room temperature to 900 ° C. over 10 hours. It was fired at 900 ° C. for 5 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was switched off and the alumina boat was allowed to cool naturally while still in the furnace. As a result, the temperature of the furnace drops to about 200 ° C. after 5 hours, but the rate of temperature decrease thereafter is rather slow. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and crushed in an agate automatic mortar for several minutes in order to make the particle size uniform. In this way, the lithium transition metal composite oxide LiNi _1/3 Co _1/3 Mn _1/3 O _{2 according} to Reference Example 1-1 was prepared.

(Reference Example 1-2-1-5)
Reference Example 1-1, except that the amount of lithium fluoride added was changed to 0.012 g, 0.018 g, 0.024 g, or 0.030 g, respectively, when the mixed powder was prepared in the firing step. In the same manner as in the above, the lithium transition metal composite oxide LiNi _1/3 Co _1/3 Mn _1/3 O _{2 according} to Reference Examples 1-2 to 1-5 was prepared.

(Reference Examples 1-6, 1-7)
In the firing step, in the same manner as in Reference Example 1, 0.012 g of lithium sulfate or 0.008 g of lithium phosphate was added instead of lithium fluoride when the mixed powder was prepared. Lithium transition metal composite oxides LiNi _1/3 Co _1/3 Mn _1/3 O _{2 according} to Reference Examples 1-6 and 1-7 were prepared, respectively.

(Reference Examples 1-8 to 1-12)
In the precursor preparation step, the molar ratio of Ni: Co: Mn was changed from 1: 1: 1, 6: 0: 4, 5: 0: 5, 5: 1: 4, 5: 2: 3, respectively. _{LiNi transition metal composite oxide LiNi 0.6} Mn _0.4 O 2 according to Reference Examples 1-8 to 1-12, respectively, in the same manner as in Reference Example 1-1 except that the value was changed to 5: 3: _2. , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.5 Co _0.1 Mn _0.4 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ was prepared.

(Comparative Reference Example 1-1)
_{Lithium transition metal composite oxide LiNi 1/3} Co _{1 / according to} Comparative Reference Example 1-1 in the same manner as in Reference Example 1-1 except that an aqueous ammonium fluoride solution is not added in the precursor preparation step. ₃ Mn _1/3 O ₂ was prepared.

(Comparative Reference Example 1-2)
Lithium transition metal composite oxide LiNi according to Comparative Reference Example 1-2 in the same manner as in Reference Example 1-1, except that lithium fluoride is not added when preparing the mixed powder in the firing step. _1/3 Co _1/3 Mn _1/3 O ₂ was prepared.

(Comparative Reference Example 1-3)
Similar to Reference Example 1-1, except that an ammonium fluoride aqueous solution is not added in the precursor preparation step and lithium fluoride is not added when preparing the mixed powder in the firing step. , Lithium transition metal composite oxide LiNi _1/3 Co _1/3 Mn _1/3 O _{2 according} to Comparative Reference Example 1-3 was prepared.

The above conditions were applied to the lithium transition metal composite oxides according to Reference Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3 using an X-ray diffractometer (manufactured by Rigaku, model name: MiniFlex II). The crystal structure was confirmed by performing powder X-ray diffraction measurement in the above, and FWHM (104) was determined. Moreover, the porosity was measured under the above conditions. As a result, it was confirmed that the lithium transition metal composite oxide according to the above reference example and the comparative reference example has an α-NaFeO _{2 structure.} X-ray diffraction measurements were also performed on all the reference examples and the lithium transition metal composite oxides according to the comparative reference examples described later, and the crystal structure was confirmed, FWHM (104) was determined, and the porosity was measured. The lithium transition metal composite oxides according to all the reference examples and comparative reference examples described later also had an α-NaFeO ₂ structure.

<Manufacturing positive electrodes for non-aqueous electrolyte secondary batteries>
Using the lithium transition metal composite oxides according to Reference Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3 as positive electrode active materials for non-aqueous electrolyte secondary batteries, refer to the procedure below. The positive electrodes for non-aqueous electrolyte secondary batteries according to Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3 were produced. Using N-methylpyrrolidone as a dispersion medium, a coating paste in which the positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were kneaded and dispersed at a mass ratio of 90: 5: 5 was prepared. The coating paste was applied to one surface of an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate. The mass and coating thickness of the active material applied per fixed area were unified so that the test conditions would be the same for the non-aqueous electrolyte secondary batteries according to all the reference examples and the comparative reference examples.

<Manufacturing negative electrodes for non-aqueous electrolyte secondary batteries>
A graphite electrode was used as the negative electrode of the non-aqueous electrolyte secondary battery.
The graphite electrode is a coating paste in which graphite, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are kneaded and dispersed in a mass ratio of 96.7: 2.1: 1.2 using water as a dispersion medium. Was applied to one side of a copper foil current collector having a thickness of 10 μm and dried. The coating amount of the coating paste was adjusted so that the capacity of the battery was not limited by the negative electrode when combined with the positive electrode plate.

<Non-aqueous electrolyte>
_{As a non-aqueous electrolyte, LiPF 6} was dissolved in a mixed solvent having an ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) volume ratio of 30:35:35 so that the concentration was 1 mol / L. The solution was used.

<Manufacturing of non-aqueous electrolyte secondary battery>
An electrode body is prepared by laminating a positive electrode, the graphite electrode, and a separator prepared by using the lithium transition metal composite oxides according to Reference Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3, respectively. did.
As a separator, a polypropylene microporous membrane surface-modified with polyacrylate was used. For the exterior body, a metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used. The electrode body is housed in the outer body so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside, and the fusion allowance in which the inner surfaces of the metal resin composite film face each other is excluded from the portion serving as the liquid injection hole. After hermetically sealing and injecting the non-aqueous electrolyte, the injection holes are sealed, and the non-aqueous electrolyte secondary according to Reference Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3 A battery was manufactured.

<Initial charge / discharge process>
The non-aqueous electrolyte secondary batteries according to each reference example and comparative reference example were initially charged and discharged for two cycles at 25 ° C. Charging was a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.35 V, and the charge termination condition was the time when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V. Here, a rest process of 10 minutes was provided after charging and after discharging. The initial discharge capacity was confirmed.

<Charge / discharge cycle test>
Subsequently, a 100-cycle charge / discharge cycle test was performed. Charging was a constant current constant voltage charging with a current of 1C and a voltage of 4.35V, and the charging termination condition was the time when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 1C and a final voltage of 2.0V. Here, a rest process of 10 minutes was provided after charging and after discharging.
The percentage of the discharge capacity in the 100th cycle to the discharge capacity in the first cycle in the charge / discharge cycle test was calculated and used as the "cycle capacity retention rate (%)".

The molar ratio of Ni: Co: Mn of the lithium transition metal composite oxide in the non-aqueous electrolyte secondary battery according to Reference Examples 1-1 to 1-12 and Comparative Reference Examples 1-1 to 1-3, firing temperature, FWHM ( 104) and the void ratio, the solvent composition of the non-aqueous electrolyte, and the cycle capacity retention rate are shown in Table 1.

From Table 1, Li (Ni _a Co _b Mn _c ) O ₂ (0.3 ≦ a ≦ 0.6, 0 ≦ b ≦ 0.4, 0.2 ≦ c ≦ 0.5, a + b + c = 1). The FWHM (104) of the lithium transition metal composite oxide having the same composition does not change much under the same firing temperature conditions, but the porosity changes depending on the preparation conditions of the precursor and the presence or absence of the sintering aid. You can see that. The cycle capacity retention rate of the battery containing these lithium transition metal composite oxides as an active material is high in the case of the reference example having a porosity of 3.5 or less, and the porosity exceeds 3.5%. In the case of the reference example, it can be seen that it has decreased.

(Reference example 2)
(Reference Example 2-1)
In the precursor preparation step, 473.1 g of nickel sulfate hexahydrate, 281.1 g of cobalt sulfate heptahydrate, and 289.3 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 4 L of ion-exchanged water. A hydroxide precursor was prepared in the same manner as in Reference Example 1-1, except that a 1.0 M sulfate aqueous solution having a Ni: Co: Mn molar ratio of 45:25:30 was prepared.
In the firing step, 0.886 g of lithium hydroxide monohydrate and 0.006 g of lithium fluoride were added to 1.897 g of the hydroxide precursor, and the molar ratio of Li :( Ni, Co, Mn): F was increased. Baking (the firing temperature of the pellets is 900 ° C.) was carried out in the same manner as in Reference Example 1-1 except that the mixed powder was prepared so as to be 1: 1: 0.01, and the present invention relates to Reference Example 2-1. Lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O ₂ was prepared.

(Reference Example 2-2-2-6)
In the firing step, the firing temperature of the pellets was changed from 900 ° C. to 920 ° C., 940 ° C., 960 ° C., 980 ° C., and 1000 ° C., respectively, in the same manner as in Reference Example 2-1. _{LiNi 0.45} Co _0.25 Mn _0.30 O ₂ of the lithium transition metal composite oxide according to Reference Example 2-2-2-6 was prepared. A photograph of the particles of the lithium transition metal composite oxide according to Reference Example 2-4 is shown in FIG.

(Reference Examples 2-7 to 2-9)
Reference except that the molar ratio of Ni: Co: Mn was changed from 45:25:30 to 40:30:30, 50:25:25, and 55:20:25, respectively, in the precursor preparation step. Similar to Example 2-4, LiNi transition metal composite oxides LiNi _0.40 Co _0.30 Mn _0.30 O ₂ and LiNi _0.50 Co _0. to prepare a _{25 Mn 0.25 O 2, LiNi 0.55} Co 0.20 Mn 0.25 O 2.

(Reference Examples 2-10, 2-11)
Similar to Reference Example 2-6, except that the molar ratio of Ni: Co: Mn was changed from 45:25:30 to 60: 0:40 and 50: 0:50, respectively, in the precursor preparation step. Then, the lithium transition metal composite oxides LiNi _0.60 Mn _0.40 O ₂ and LiNi _0.50 Mn _0.50 O _{2 according} to Reference Examples 2-10 and 2-11 were prepared, respectively.

(Reference Example 2-12)
In the firing step, in the same manner as in Reference Example 2-4, Reference Example 2-, except that 0.012 g of lithium sulfate was added instead of 0.006 g of lithium fluoride when preparing the mixed powder. Lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O _{2 according} to No. 12 was prepared.

(Reference Example 2-13)
In the firing step, Reference Example 2 was carried out in the same manner as in Reference Example 2-4, except that 0.008 g of lithium phosphate was added instead of 0.006 g of lithium fluoride when the mixed powder was prepared. Lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O _{2 according} to -13 was prepared.

(Reference Example 2-14)
In the precursor preparation step, a hydroxide precursor was prepared without adding an aqueous solution of ammonium fluoride, and in the firing step, 0.009 g of ammonium fluoride was added instead of 0.006 g of lithium fluoride, and Li: The present invention relates to Reference Example 2-14 in the same manner as in Reference Example 2-6, except that the mixed powder was prepared so that the molar ratio of (Ni, Co, Mn): F was 1: 1: 0.01. Lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O ₂ was prepared.

(Comparative Reference Examples 2-1 and 2-2)
In the firing step, the firing temperature of the pellets was changed from 900 ° C. to 880 ° C. and 1050 ° C., respectively, in the same manner as in Reference Example 2-1 and Comparative Reference Examples 2-1 and 2-, respectively. _{LiNi 0.45} Co _0.25 Mn _0.30 O ₂ of the lithium transition metal composite oxide according to No. 2 was prepared.

(Comparative Reference Example 2-3)
Similar to Reference Example 2-1 except that an ammonium fluoride aqueous solution is not added in the precursor preparation step and lithium fluoride is not added when preparing the mixed powder in the firing step. , Lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O _{2 according} to Comparative Reference Example 2-3 was prepared. A photograph of the particles of the lithium transition metal composite oxide according to Comparative Reference Example 2-3 is shown in FIG.

(Comparative Reference Example 2-4)
Lithium transition metal composite oxide LiNi _0.45 Co _{0. 25} Mn _0.30 O ₂ was prepared.

(Comparative Reference Example 2-5)
Lithium transition metal composite oxide LiNi according to Comparative Reference Example 2-5 in the same manner as in Reference Example 2-1 except that lithium fluoride is not added when preparing the mixed powder in the firing step. _0.45 Co _0.25 Mn _0.30 O ₂ was prepared.

(Comparative Reference Examples 2-6, 2-7)
In the precursor preparation step, the molar ratio of Ni: Co: Mn was changed from 45:25:30 to 80:10:10, and in the firing step, the firing temperature of the pellets was changed from 900 ° C. , 700 ° C. and 800 ° C., respectively, in the same manner as in Reference Example 2-1. LiNi transition metal composite oxide LiNi _0.80 Co _{0.10 according to Comparative Reference Examples 2-6 and 2-7, respectively.} Mn _0.10 O ₂ was prepared.

<Manufacturing of non-aqueous electrolyte secondary battery>
A positive electrode produced in the same manner as in Reference Example 1-1, except that the lithium transition metal composite oxides according to Reference Examples 2-1 to 2-14 and Comparative Reference Examples 2-1 to 2-7 were used as the positive electrode active materials, respectively. , The graphite electrode (negative electrode), and the non-aqueous electrolyte are used in the same manner as in Reference Example 1-1. A water electrolyte secondary battery was manufactured.

<Initial charge / discharge process>
The produced non-aqueous electrolyte secondary battery was subjected to an initial charge / discharge step at 25 ° C. Charging was a constant current constant voltage charge with a current of 0.1 C and a voltage of 4.6 V, and the charge termination condition was set to the time when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 C and a final voltage of 2.0 V. This charge / discharge was performed for 2 cycles. Here, a pause process of 30 minutes was provided after charging and after discharging.

<Charge / discharge cycle test>
Subsequently, a 100-cycle charge / discharge cycle test was performed under the same conditions as in Reference Example 1.
The percentage of the discharge capacity in the 100th cycle to the discharge capacity in the first cycle in the charge / discharge cycle test was calculated and used as the "cycle capacity retention rate (%)".

Ni: Co: Mn molar ratio of lithium transition metal composite oxide in the non-aqueous electrolyte secondary battery according to Reference Examples 2-1 to 2-14 and Comparative Reference Examples 2-1 to 2-7, FWHM (104), Table 2 shows the results of the porosity and the 1C capacity retention rate.

From Table 2, the lithium transition metal composite oxide having FWHM (104) in the range of 0.125 to 0.145 ° and the void ratio in the range of 1.5 to 3.5% is used as the positive electrode active material. It can be seen that the non-aqueous electrolyte secondary battery used (Reference Examples 2-1 to 2-14) has a high cycle capacity retention rate and excellent charge / discharge cycle performance.
On the other hand, when the FWHM (104) is smaller than 0.125 or larger than 0.145 °, the cycle capacity retention rate is low (see Comparative Reference Examples 2-1, 2-2, 2-7). ). Further, even if the FWHM (104) is in the range of 0.125 to 0.145 °, if the porosity exceeds 3.5%, the cycle capacity retention rate becomes low (Comparative Reference Examples 2-3 to 2). -6).
Therefore, from this reference example, in order to improve the charge / discharge cycle performance, it is necessary to set the FWHM (104) to 0.125 to 0.145 ° and the porosity to 1.5 to 3.5%. It turns out that there is.

Further, in Reference Example 2, LiF and Li as sintering aids are added to a precursor obtained by co-precipitating a compound containing Ni, Co and Mn in a solution containing _{fluorine ion (NH 4 F).} Lithium transition metal composite oxidation in which FWHM (104) is 0.125 to 0.145 ° and void ratio is 1.5 to 3.5% by firing with ₂ SO ₄ and Li ₃ PO _{4 contained.} A positive electrode active material of a product can be produced.
If the firing temperature is too low, the porosity may be larger than 3.5% (Comparative Reference Examples 2-1 and 2-6), and the FWHM (104) may be larger than 0.145 ° (Comparative Reference Example). 2-1) If the firing temperature is too high, the FWHM (104) becomes smaller than 0.125 ° (Comparative Reference Example 2-2). Therefore, in order to improve the charge / discharge cycle performance, the firing temperature is 900 to 1000. The temperature is preferably set to ° C.
Further, if the Ni content is too large, the FWHM (104) may be smaller than 0.125 ° (Comparative Reference Example 2-7), so that the molar ratio of Ni to the transition metal element Me, Ni / Me, is 0. It is preferably set to 0.3 to 0.6.

(Example 1-1)
The lithium transition metal composite oxide LiNi _0.45 Co _0.25 Mn _0.30 O ₂ prepared in Reference Example 2-1 was used as the positive electrode active material, and as a non-aqueous electrolyte, ethylene carbonate (EC): dimethyl carbonate ( The non-aqueous electrolyte secondary battery according to Example 1-1 was produced in the same manner as in Reference Example 1-1 except that a non-aqueous solvent having a volume ratio of DMC) of 30:70 was used.

[Evaluation of low temperature performance]
The non-aqueous electrolyte secondary batteries according to Example 1-1 were divided into two groups and subjected to the initial charge / discharge step at 25 ° C. and 0 ° C., respectively. Charging was a constant current constant voltage charging with a current of 0.1 CmA and a voltage of 4.6 V, and the charging termination condition was the time when the current value was attenuated to 1/6. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. This charging / discharging is performed for 2 cycles, a pause process of 30 minutes is provided after charging and discharging, and the initial capacity at 25 ° C. and 0 ° C. is measured, and the ratio of the initial capacity at 0 ° C. to the initial capacity at 25 ° C. is calculated. This was used to evaluate the low temperature performance.

[Charge / discharge cycle test]
Subsequently, in the same manner as in Reference Example 1, a 100-cycle charge / discharge cycle test is performed, and the percentage of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle in the charge / discharge cycle test is calculated, and the “cycle capacity maintenance” is performed. Rate (%) ”.
The evaluation of the low temperature performance and the charge / discharge cycle test were carried out in the same manner as in Example 1-1 for the non-aqueous electrolyte secondary batteries according to all Examples and Comparative Examples described later.

(Examples 1-2 to 1-6, Comparative Examples 1-1 and 1-2)
The same as in Example 1-1, except that the lithium transition metal composite oxide prepared in Reference Examples 2-2-2-6 and Comparative Reference Examples 2-1 and 2-2 was used as the positive electrode active material. , Examples 1-2 to 1-6, and Comparative Example 1-1 and Comparative Example 1-2 were produced.

Regarding the non-aqueous electrolyte secondary batteries according to Examples 1-1 to 1-6 and Comparative Examples 1-1 and 1-2, the FWHM (104), porosity, and firing of the lithium transition metal composite oxide used as the active material. Temperature and molar ratio of Ni: Co: Mn; solvent composition of non-aqueous electrolyte and volume ratio of DMC in chain carbonate; cycle capacity retention rate; and low temperature performance (0 ° C / 25 ° C volume ratio [%]) Is shown in Table 3.

According to Table 3, regarding the cycle capacity retention rate, the non-aqueous electrolyte secondary battery (FWHM (104) of lithium transition metal composite oxide) according to Examples 1-1 to 1-6 has a temperature of 0.125 to 0.145 °. , The void ratio is in the range of 1.5 to 3.5%), whereas the non-aqueous electrolyte secondary battery (lithium transition metal composite oxide) according to Comparative Examples 1-1 and 1-2 is excellent. It can be seen that (104) FWMF and / or the void ratio is not in the above range), which is the same tendency as in Reference Example 2.
On the other hand, the non-aqueous electrolyte secondary batteries according to Examples 1-1 to 1-6 and Comparative Examples 1-1 and 1-2 contain cyclic carbonate and chain carbonate in a volume ratio of 30:70 and are chain-like. It can be seen that it has a non-aqueous electrolyte containing a non-aqueous solvent in which the carbonate is DMC, and has excellent low temperature performance.

(Examples 2-1 to 2-6, Comparative Examples 2-1 and 2-2)
The solvent composition in the non-aqueous electrolyte is the same as in Examples 1-1 to 1-6 and Comparative Examples 1-1 and 1-2, respectively, except that the volume ratio is changed to EC: DMC: EMC = 30: 35: 35. Then, the non-aqueous electrolyte secondary batteries according to Examples 2-1 to 2-6 and Comparative Examples 2-1 and 2-2 (Reference Examples 2-1 to 2-6, Comparative Reference Examples 2-1 and 2). The same battery as the non-aqueous electrolyte secondary battery according to -2) was produced.

(Example 2-7)
The non-aqueous electrolyte according to Example 2-7 is the same as in Example 1-1 except that the solvent composition in the non-aqueous electrolyte is changed to a mixed solvent of EC: DMC: DEC at 30:35:35 in volume ratio. A secondary battery was manufactured.
Table 4 shows the results of the cycle capacity retention rate and low temperature performance evaluation for these batteries.

According to Table 4, even when a non-aqueous electrolyte solution having a DMC volume ratio of 50% in the chain carbonate in the non-aqueous solvent is used, the cycle capacity retention rate is described in Reference Examples 2-1 to 2-6, Comparative Reference. As shown in Table 2 for Examples 2-1 and 2-2, the lithium transition metal composite oxide has a FWHM (104) of 0.125 to 0.145 ° and a porosity of 1.5 to 3.5%. The non-aqueous electrolyte secondary battery according to Examples 2-1 to 2-6 in the range is FWHM (104), and the void ratio is not in the above range with respect to the battery according to Comparative Examples 2-1 and 2-2. , It can be seen that it has an excellent effect. Further, from Example 2-7, it can be seen that even if the chain carbonate to be combined with DMC is changed from EMC to DEC, the cycle capacity retention rate is excellent.
On the other hand, regarding the low temperature performance, since the non-aqueous electrolyte secondary batteries according to the examples and the comparative examples all secure 80% or more, it can be seen that they have a certain effect.

(Examples 3-1 and 3-2)
According to Example 3-1 and Example 3-2, respectively, in the same manner as in Example 1-1 except that the volume ratio of EC: DMC in the non-aqueous electrolyte was changed to 20:80 and 40:60, respectively. A non-aqueous electrolyte secondary battery was manufactured.

(Examples 3-3, 3-4)
The non-aqueous solvent in the non-aqueous electrolyte was changed to a mixed solvent having a volume ratio of FEC: DMC of 30:70 and a volume ratio of PC: DMC of 30:70. The non-aqueous electrolyte secondary battery according to 3-3 and Example 3-4 was produced.
Table 5 shows the results of the cycle capacity retention rate and low temperature performance evaluation for these batteries.

From the results of Examples 3-1 and 3-2, even when the volume ratio of the chain carbonate to the non-aqueous solvent is 60% or 80%, the non-aqueous electrolyte is excellent in low temperature performance and charge / discharge cycle performance. It can be seen that a secondary battery can be obtained.
From Examples 3-3 and 3-4, it can be seen that the effect of the present invention can be obtained even if FEC or PC is used as the cyclic carbonate in addition to EC.

(Examples 4-1 and 4-2)
The same batteries as those according to Reference Examples 2-8 and 2-9 were prepared, and the low temperature performance and charge / discharge cycle performance were evaluated.
The results are shown in Table 6 together with Examples 2-4.

From Table 6, the lithium transition metal composite oxide used in the active material has an α-NaFeO ₂ structure, FWHM (104) is 0.125 to 0.145 °, and the void ratio is 1.5 to 3.5%. When the above conditions are satisfied, it can be seen that a non-aqueous electrolyte secondary battery having excellent low temperature performance and charge / discharge cycle performance can be obtained.

(Example 5-1 and Comparative Examples 5-1 to 5-4)
Example 5-1 in the same manner as in Example 2-1 except that the volume ratio of DMC in the chain carbonate contained in the non-aqueous electrolyte was set to 40%, 30%, 20%, 10%, and 0%. A non-aqueous electrolyte secondary battery according to ~ 5-4 and Comparative Example 5-1 was prepared, and the low temperature performance and the charge / discharge cycle performance were evaluated.
The results are shown in Table 7 together with Examples 1-1 and 2-1.

From Table 7, it can be seen that as the volume ratio of DMC to the chain carbonate decreases from 100%, the cycle capacity retention rate increases, but the low temperature performance decreases. Therefore, in order to obtain the effect of excellent both low temperature performance and charge / discharge cycle performance, the volume ratio of DMC to the chain carbonate is preferably 10% or more, and more preferably 30% or more.

(Comparative Examples 6-1 to 6-5)
Comparative Example 6-1 in the same manner as in Comparative Example 1-1, except that the volume ratio of DMC in the chain carbonate contained in the non-aqueous electrolyte was 40%, 30%, 20%, 10%, and 0%. A non-aqueous electrolyte secondary battery according to ~ 6-5 was prepared, and the low temperature performance and the charge / discharge cycle performance were evaluated.
The results are shown in Table 8 together with Comparative Example 1-1 and Comparative Example 2-1.

As shown in Table 8, the FWHM (104) of the lithium transition metal composite oxide used as the active material does not satisfy 0.125 to 0.145 °, and the void ratio is 1.5 to 3.5%. The non-aqueous electrolyte secondary battery according to the comparative example which does not satisfy the above is the same as the non-aqueous electrolyte secondary battery according to the example in Table 7 in that the low temperature performance tends to decrease as the DMC decreases. That is, when the volume ratio of DMC is 30%, in Example 5-2 and Comparative Example 6-2, the volume ratio of 0 ° C./25 ° C. is 80%, and the volume ratio of DMC is 10%. In Examples 5-4 and Comparative Example 6-4, the volume ratio of 0 ° C./25 ° C. is 77%. On the other hand, in the non-aqueous electrolyte secondary battery according to the above comparative example, the cycle capacity retention rate is 97% in Example 5-2 when the volume ratio of DMC is 30%, whereas it is 97% in Comparative Example 6. In -2, it is 83%, and when the volume ratio of DMC is 10%, it is 98% in Example 5-4, whereas it is 93% in Comparative Example 6-4, so the volume of DMC. It can be seen that even if the ratio is reduced to 10%, only a cycle capacity retention rate of at most 93% can be obtained.
Therefore, in order to obtain the effect of excellent low temperature performance and charge / discharge cycle performance, a lithium transition metal having a FWHM (104) of 0.125 to 0.145 ° and a porosity of 1.5 to 3.5% is satisfied. It can be said that the composite oxide is used as an active material, and the volume ratio of DMC is preferably 10% or more, and more preferably 30% or more.

By providing the positive electrode active material and the non-aqueous electrolyte of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having excellent low temperature performance and charge / discharge cycle performance. Therefore, an electric vehicle (EV) and a hybrid electric vehicle (HEV) can be provided. ), It is useful as a power source for plug-in hybrid electric vehicles (PHEV) and the like.

1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (2)

A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte.
The positive electrode has an α-NaFeO ₂ structure, the half-value width of the diffraction peak at 2θ: 44 ± 1 ° in the powder X-ray diffraction diagram using CuKα rays is 0.125 to 0.145 °, and the void ratio is lithium transition metal composite oxide is 1.5 to 3.5% (however, "compositional formula _{Li a Mn 0.5-x Ni 0.5} -y M x + y O 2 ( where 0 <a <1.3, -0.1 ≤ x-y ≤ 0.1, M contains "composite oxides represented by elements other than Li, Mn, and Ni)" as an active material.
The non-aqueous electrolyte contains a non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the volume ratio of the chain carbonate to the non-aqueous solvent is 60% or more, and the dimethyl carbonate accounts for the chain carbonate. A non-aqueous electrolyte secondary battery having a volume ratio of 10% or more. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a molar ratio of Ni to the transition metal element Me, Ni / Me, of 0.4 to 0.6.

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