JP2016167446A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increase of resistance caused by the charging/discharging cycle of a lithium secondary battery using a "lithium excess type" positive electrode active material.SOLUTION: In a lithium secondary battery including a positive electrode, a negative electrode and nonaqueous electrolyte, the positive electrode has an α-NaFeOstructure, contains Co, Ni and Mn as transition metal Me, and contains a positive electrode active material in which at least one kind of element selected from Al, Zr and Ti exists on the particle surfaces of lithium-transition metal composite oxide of a molar ratio Li/Me>1 and a molar ratio Mn/Me>0.5. The negative electrode contains a negative electrode active material comprising a carbon material, sulfur existing on the negative electrode, and the nonaqueous electrolyte containing fluoroethylene carbonate.SELECTED DRAWING: None

Description

  The present invention relates to a lithium secondary battery using a lithium transition metal composite oxide as a positive electrode active material and carbon as a negative electrode active material, and particularly relates to a lithium secondary battery using a specific electrolyte.

Conventionally, as a positive electrode active material for a lithium secondary battery, a “LiMeO ₂ type” active material (Me is a transition metal) having an α-NaFeO ₂ type crystal structure has been studied, and lithium secondary batteries using LiCoO ₂ have been widely put into practical use. It was converted. However, the discharge capacity of LiCoO ₂ was about 120 to 130 mAh / g. As Me, it has been desired to use abundant Mn as a global resource. However, the “LiMeO ₂ type” active material containing Mn as Me, when the molar ratio of Mn to Me, Mn / Me exceeds 0.5, the structure changes to spinel type when charged, Since the structure could not be maintained, there was a problem that the charge / discharge cycle performance was extremely inferior.

Accordingly, various “LiMeO ₂ type” active materials having a Mn to Me molar ratio Mn / Me of 0.5 or less and excellent in charge / discharge cycle performance have been proposed and partially put into practical use. For example, LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ have a discharge capacity of 150 to 180 mAh / g.

In recent years, Me contains Ni, Co, and Mn, and a molar ratio of Mn to Me, Mn / Me, containing a lithium transition metal composite oxide exceeding 0.5, can maintain an α-NaFeO ₂ structure even when charged. A positive electrode active material has been proposed (see Patent Documents 1 and 2).

In Patent Documents 1 and 2, when a positive electrode active material containing Ni, Co and Mn as Me and having a molar ratio Mn to Me of Mn / Me exceeding 0.5 is used, 4.3 V (vs. Li / Li ⁺ )) And 4.8V or less (vs. Li ^/ Li ⁺ ), which appears in the positive electrode potential range, and is charged at the time of use by providing a manufacturing process for charging at least the region where the potential change is relatively flat. Even when a charging method in which the maximum potential of the positive electrode at the time is 4.3 V (vs. Li / Li ⁺ ) or less or less than 4.4 V (vs. Li ^/ Li ⁺ ) is employed, 200 mAh / g It is described that a battery capable of obtaining the above discharge capacity can be manufactured.

Thus, unlike the case of the conventional “LiMeO ₂ type” positive electrode active material, in the positive electrode active material containing Ni, Co and Mn as Me and having a molar ratio of Mn to Me, Mn / Me exceeding 0.5, It is characterized in that a high discharge capacity can be obtained by performing a relatively high potential exceeding 4.3 V, particularly a potential of 4.4 V or higher, at least in the first charge.
In this positive electrode active material, the raw materials are mixed so that the composition ratio Li / Me of lithium (Li) with respect to the ratio of transition metal (Me) is larger than 1, for example, Li / Me is 1.25 to 1.6. Therefore, it is also called a “lithium-excess type” active material, and the composition after synthesis can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

  Further, a positive electrode in which an oxide of at least one metal element selected from the group consisting of Zr, Ti, and Al is present on the surface of the above-described “lithium-excess” active material (lithium transition metal composite oxide) particles Active materials are also known (see Patent Documents 3 and 4), and it is also known to use a material containing fluoroethylene carbonate as a non-aqueous electrolyte for a lithium secondary battery using a “lithium-rich” positive electrode active material. Yes (see Patent Documents 4 and 5).

Patent Document 3 includes “Li element and at least one transition metal element selected from the group consisting of Ni, Co, and Mn (provided that the molar amount of Li element is the total molar amount of the transition metal element). It is more than 1.2 times.) It is composed of particles (II) in which the oxide (I) of at least one metal element selected from Zr, Ti, and Al is unevenly distributed on the surface of the lithium-containing composite oxide. A positive electrode active material for a lithium ion secondary battery characterized by the above. "(Claim 1) is described.
Further, as an object of the present invention, “a positive electrode active material for a lithium ion secondary battery excellent in cycle characteristics and rate characteristics even when charged at a high voltage, a positive electrode, a lithium ion secondary battery, and a positive electrode for a lithium ion secondary battery” "Provide a method for producing an active material" (paragraph [0007]).

In Patent Document 4, "in a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent, the positive electrode active material includes: Composition of the general formula xLi [Li _1/3 Mn _2/3 ] O ₂ · (1-x) LiMO ₂ (0 <x ≦ 1, M is one or more transition metal elements selected from Ni, Co, Mn) A non-aqueous electrolyte secondary battery comprising a lithium-containing transition metal oxide having the formula, wherein the non-aqueous solvent contains a fluorinated cyclic carbonate in which a fluorine atom is directly bonded to a carbonate ring. Item 1), "The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the fluorinated cyclic carbonate is 4-fluoroethylene carbonate." 8), “Al-containing oxide and / or Al-containing hydroxide adheres to the surface of the positive electrode active material particles. Others are described invention of the non-aqueous electrolyte secondary battery according to any one of claims 1 to 11, characterized in that it is covered. "(Claim 12).
Further, an object of the present invention is “a nonaqueous electrolyte secondary battery containing a lithium-containing transition metal oxide that releases oxygen at the time of initial charge as a positive electrode active material, having a high discharge capacity and cycle characteristics at a high voltage. To provide a non-aqueous electrolyte secondary battery excellent in (paragraph [0011]).

Further, Patent Document 4 states that “These lithium-containing transition metal oxides preferably cover the surface of the lithium-containing transition metal oxide with fine particles of an inorganic compound such as Al ₂ O ₃ . It is preferable that the protruding Al-containing oxide and / or Al-containing hydroxide is uniformly dispersed and adhered or coated on the surface of the transition metal oxide. This is because decomposition of the non-aqueous electrolyte in the state is suppressed and the high voltage cycle characteristics are further improved ”(paragraph [0028]),“ The non-aqueous electrolyte used in the present invention is a non-aqueous solvent. Contains fluorinated cyclic carbonates in which fluorine atoms are directly bonded to the carbonate ring.The fluorinated cyclic carbonates in which fluorine atoms are directly bonded to the carbonate ring include ethylene Examples include those in which hydrogen bonded to the carbonate ring of the carbonate is substituted with a fluorine atom, and the like, for example, etc. Among them, 4-fluoroethylene carbonate has a relatively low viscosity and is a protective film on the negative electrode. Is highly formed ”(paragraphs [0034] to [0036]).

Patent Document 5 states that “a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte solution, wherein the positive electrode includes a compound represented by the following formula (1) as a positive electrode active material, The liquid includes a solvent composed of a cyclic carbonate and a chain carbonate, the chain carbonate is composed of a compound having no methoxy group, and the cyclic carbonate includes a fluorinated cyclic carbonate. .
_{xLi 2 MO 3 - (1-} x) LiAO 2 ··· (1)
(M is at least one element of Mn, Ti, and Zr, and A is at least one element of Ni, Co, Mn, Fe, Ti, Zr, Al, Mg, Cr, and V. 0 <x <1) ”(Claim 1),“ The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate, and the fluorinated cyclic carbonate includes fluoroethylene carbonate and difluoroethylene carbonate. The lithium carbonate secondary battery according to claim 1, wherein the chain carbonate is diethyl carbonate ”(claim 2).
Further, “Providing a lithium ion secondary battery excellent in cycle characteristics and stability” (paragraph [0008]) is described as an object of the present invention.

  It is also known to use a non-aqueous electrolyte secondary battery (lithium secondary battery) containing a cyclic sulfonic acid compound as the electrolyte solution of the above-described “lithium-rich” positive electrode active material (see Patent Document 6). ).

Patent Document 6 states that “a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, where the positive electrode has an α-NaFeO ₂ type crystal structure and has a composition formula Li _{1 + α} Me _1-α. A positive electrode active material containing a lithium transition metal composite oxide represented by O ₂ (Me is a transition metal element containing Mn, Ni and Co, 1.0 ≦ (1 + α) / (1-α) ≦ 1.6) And the non-aqueous electrolyte contains a cyclic sulfonic acid compound represented by the following general formula (1): a non-aqueous electrolyte secondary battery. ).
Further, as an object of the present invention, “a positive electrode active material having an α-NaFeO ₂ type crystal structure and including a lithium transition metal composite oxide containing Co, Ni, and Mn, especially a“ lithium-excess type ”positive electrode active material was used. "Improvement of charge / discharge cycle performance of a nonaqueous electrolyte secondary battery over a nonaqueous electrolyte containing a specific cyclic sulfonic acid compound" (paragraph [0014]) is described.

Furthermore, Patent Document 6 states that “the mechanism of action of the above cyclic sulfonic acid compound is not always clear. The following is an estimate of charge / discharge cycle performance improvement when a nonaqueous electrolyte containing diglycol sulfate (DGLST) is used. In the positive electrode having a α-NaFeO ₂ type crystal structure and containing a lithium transition metal composite oxide containing Mn as a positive electrode active material, Mn is eluted from the positive electrode into the electrolyte during charge and discharge. The Mn reaches the negative electrode, and a film containing Mn is formed on the negative electrode, and this Mn-containing film is considered to be the cause of reducing the battery life such as cycle characteristics. reductive decomposition potential is about 1.1V (vs.Li/Li ^+), relatively higher than other common solvents, nonaqueous other solvent during the first charge of the electrolyte secondary battery First, a DGLST-derived film is formed on the negative electrode, and at the time of the reductive decomposition, a part containing sulfonic acid is separated, and this part supplements Mn generated by dissolution from the positive electrode. Therefore, it is considered that the life of the non-aqueous electrolyte secondary battery such as cycle characteristics is improved by including DGLST in the non-aqueous electrolyte. (Paragraph [0034]), “composition formula Li _{1 + α} Me _1-α O ₂ (Me is a transition metal element containing Mn, Ni and Co, 1.0 <(1 + α) / (1-α) ≦ 1.6 The batteries of Examples 1 to 9 using a non-aqueous electrolyte containing diglycol sulfate (DGLST) as a “Li-excess type” positive electrode active material containing a lithium transition metal composite oxide represented by DGLST Compared to the battery of Comparative Example 1 using a non-aqueous electrolyte that does not contain, the cycle capacity retention rate (charge / discharge cycle performance) is improved, and the internal resistance after cycling and the internal resistance during standing are reduced.- The battery of Comparative Example 4 using a non-aqueous electrolyte containing 1,3-propene sultone (PRS) is improved in internal resistance as compared with the case where it is not contained, but the cycle capacity maintenance rate is reduced. The battery thickness increases "(paragraph [0102]).

WO2012 / 091015 WO2013 / 084923 WO2012 / 057289 JP 2011-34943 A JP 2013-206561 A JP 2014-89800 A

As described above, the surface of the particles of the “lithium-rich” positive electrode active material is modified with different elements (Al, Zr, Ti), and the electrolysis of the lithium secondary battery using the “lithium-rich” cathode active material. Although it is known to improve cycle characteristics (charge / discharge cycle performance) by using a liquid containing fluoroethylene carbonate or a cyclic sulfonic acid compound as the liquid, the charge / discharge cycle performance has not been sufficiently improved. Patent Document 6 also discloses that the use of a lithium secondary battery electrolyte containing a “lithium-excess type” positive electrode active material containing a cyclic sulfonic acid compound improves charge / discharge cycle performance and increases resistance. Although described as being suppressed, the effect of suppressing the increase in resistance accompanying the charge / discharge cycle was not sufficient.
In view of the above prior art, an object of the present invention is to suppress an increase in resistance associated with a charge / discharge cycle of a lithium secondary battery using a “lithium-rich” positive electrode active material.

In the present invention, in order to solve the above problems, the following means are adopted.
(1) In a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode has an α-NaFeO ₂ structure, includes Co, Ni, and Mn as transition metals Me, and has a molar ratio of Li / Me > 1, a positive electrode active material in which at least one selected from Al, Zr, and Ti is present on the particle surface of the lithium transition metal composite oxide having a molar ratio Mn / Me> 0.5, A lithium secondary battery comprising a negative electrode active material made of a carbon material, sulfur existing on the negative electrode, and the non-aqueous electrolyte containing fluoroethylene carbonate.
(2) The lithium secondary battery according to (1), wherein the non-aqueous electrolyte contains a sulfur-containing compound.

  According to the present invention, it is possible to suppress an increase in resistance accompanying a charge / discharge cycle of a lithium secondary battery using a “lithium-rich” positive electrode active material and to remarkably improve a cycle capacity maintenance rate.

1 is an external perspective view showing an embodiment of a lithium secondary battery according to the present invention. Schematic showing a power storage device in which a plurality of lithium secondary batteries according to the present invention are assembled

The present inventors have found that the “lithium-excess type” positive electrode active material has a higher capacity than the “LiMeO ₂ type” active material, but has a large resistance and further increases with the cycle. It was confirmed.
Therefore, the presence of different elements on the surface of the “lithium-rich” positive electrode active material improves the surface condition, and when a non-aqueous electrolyte additive is appropriately selected, the increase in resistance with the cycle is greatly suppressed. I found out that

  As will be described later, (a) at least one selected from Al, Zr, and Ti is used for the different element modification performed on the “lithium-rich” positive electrode active material (lithium transition metal composite oxide). Further, (b) the non-aqueous electrolyte contains fluoroethylene carbonate. Furthermore, it has been found that sulfur is present on the carbon negative electrode by adding a sulfur-containing compound to the non-aqueous electrolyte. It was experimentally confirmed that the increase in resistance accompanying the cycle of the lithium secondary battery using the “lithium-excess type” positive electrode active material is largely suppressed by the synergistic effect of the above (a), (b) and (c).

In order to obtain a high discharge capacity, the lithium transition metal composite oxide used for the positive electrode active material of the lithium secondary battery according to the present invention has a molar ratio Li / Me of the lithium (Li) to the transition metal Me of greater than 1. Lithium excess ”lithium transition metal composite oxide. Typically, this feature can be expressed as (1 + α) / (1-α)> 1, that is, α> 0 in the composition formula Li _{1 + α} Me1 _1-α O ₂ .
In particular, in order to obtain a lithium secondary battery having a large discharge capacity, the molar ratio Li / Me of the transition metal Me is set to be larger than 1.2 and smaller than 1.5, that is, the composition formula Li _{1 + α} It is preferable that 1.2 <(1 + α) / (1-α) <1.5 in Me _1-α O ₂ . In particular, from the viewpoint that a lithium secondary battery having a large discharge capacity and excellent high-rate discharge performance can be obtained, it is preferable to select one having the Li / Me of 1.25 to 1.4.

  The composition of the lithium transition metal composite oxide is such that the transition metal Me contains Co, Ni, and Mn, and the molar ratio Mn / Me> 0.5 from the viewpoint that a high discharge capacity can be obtained. The molar ratio Mn / Me is preferably 0.6 or more, and more preferably 0.6 to 0.75.

  In order to improve the initial efficiency and high rate discharge performance of the lithium secondary battery, the molar ratio Co / Me of Co to the transition metal element Me is preferably 0.05 to 0.40. More preferably, it is set to ˜0.30.

A typical example of the lithium transition metal composite oxide used for the positive electrode active material of the lithium secondary battery according to the present invention is represented by the general formula Li _{1 + α} (Co _a Ni _b Mn _c ) _1-α O ₂ , where (1 + α) / ( 1-α)> 1, a + b + c = 1, a> 0, b> 0, c> 0.5, a composite oxide composed of Li, Co, Ni, and Mn. For example, Li _1.13 Co _0.11 Ni _0.17 Mn _0.59 O ₂ (Li / Me = 1.3, Mn / Me = 0.68), Li _1.11 Co _0.11 Ni _0.18 Mn _0.60 O ₂ (Li / Me = 1.25, Mn / Me = 0.67), Li _1.15 Co _0.11 Ni _0.17 Mn _0.57 O ₂ (Li / Me = 1.35) , Mn / Me = 0.67), Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 O ₂ (Li / Me = 1.4, Mn / Me = 0.67), etc. However, in order to improve discharge capacity, it is preferable to contain 1000 ppm or more of Na. As for content of Na, 2000-10000 ppm is more preferable.

  In order to adjust the Na content to the above range, in the step of preparing a carbonate precursor described later, a sodium compound such as sodium carbonate is used as a neutralizing agent, and Na is left in the washing step, and In the subsequent firing step, a method of adding a sodium compound such as sodium carbonate can be employed.

  In addition, a small amount of other metals such as alkali metals other than Na, alkaline earth metals such as Mg and Ca, transition metals typified by 3d transition metals such as Fe and Zn, and the like are included as long as the effects of the present invention are not impaired. It does not exclude doing.

The lithium transition metal composite oxide used for the positive electrode active material of the lithium secondary battery according to the present invention has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charging and discharging) is attributed to the space group P3 ₁ 12 or R3-m. Among these, those belonging to the space group P3 ₁ 12 are superlattice peaks (Li [Li _1/3 Mn _2/3 ] O ₂ near 2θ = 21 ° on the X-ray diffraction diagram using the CuKα tube. The peak observed in the monoclinic type) is confirmed. However, when charging is performed once and Li in the crystal is desorbed, the symmetry of the crystal changes, whereby the superlattice peak disappears and the lithium transition metal composite oxide belongs to the space group R3-m. Will come to be. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

The lithium transition metal composite oxide is assigned to either the hexagonal space group P3 ₁ 12 or R3-m, and is a diffraction peak of 2θ = 18.6 ° ± 1 ° on an X-ray diffraction diagram using a CuKα tube. Is preferably 0.20 ° to 0.27 °, and / or the half width of the diffraction peak at 2θ = 44.1 ° ± 1 ° is 0.26 ° to 0.39 °. By doing so, it becomes possible to increase the discharge capacity of the positive electrode active material. The diffraction peak of 2θ = 18.6 ° ± 1 ° is a (003) plane in space group _P3 1 12 and R3-m in Miller indices hkl, the diffraction peak of 2θ = 44.1 ° ± 1 °, the The space group P3 ₁ 12 is indexed on the (114) plane, and the space group R3-m is indexed on the (104) plane.

Further, in the lithium-excess type lithium transition metal composite oxide, the oxygen position parameter obtained from the crystal structure analysis by the Rietveld method based on the X-ray diffraction pattern is 0.262 or less at the end of discharge and 0.267 or more at the end of charge. Preferably there is. Thereby, a lithium secondary battery excellent in high rate discharge performance can be obtained. Note that the oxygen positional parameter is Me (transition metal) spatial coordinates (0, 0, 0) for the α-NaFeO ₂ type crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m, This is 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). In other words, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position (see Patent Documents 1 and 2).

  In the present invention, the positive electrode active material containing the lithium transition metal composite oxide preferably has a 50% particle diameter (D50) in the particle size distribution measurement of 5 to 10 μm. By producing from a carbonate precursor, a positive electrode active material having a large discharge capacity can be obtained even if the 50% particle size (D50) in the particle size distribution measurement is 5 to 10 μm.

In the present invention, the lithium transition metal composite oxide has a peak differential fine particle size in the range of 30 to 40 nm in pore diameter, which shows the maximum differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method. The pore volume is preferably 0.85 mm ³ / (g · nm) or more. When the peak differential pore volume is 0.85 mm ³ / (g · nm) or more, a lithium secondary battery having excellent initial efficiency can be obtained. Further, by setting the peak differential pore volume to 1.76 mm ³ / (g · nm) or less, it is possible to obtain a lithium secondary battery having particularly excellent discharge capacity in addition to the initial efficiency. The volume is more preferably 0.85 to 1.76 mm ³ / (g · nm).

  In the present invention, an oxide of at least one different element selected from Al, Zr, and Ti is modified (added) to the particle surface of the lithium transition metal composite oxide as described above. A preferable addition amount of the oxide of the different element is 0.1 to 1% by mass in terms of metal.

Next, a method for producing a positive electrode active material used for the lithium secondary battery of the present invention will be described.
The positive electrode active material used in the lithium secondary battery of the present invention basically contains the metal elements (Li, Mn, Co, Ni) constituting the active material according to the composition of the active material (oxide) intended. It can be obtained by adjusting the raw materials and firing them. However, with respect to the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li raw material during firing.
In producing an oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Co, Ni, and Mn are mixed and fired, or Co, Ni, and Mn were previously present in one particle. A “coprecipitation method” is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Co and Ni, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O ₂ etc.) by solid phase method, but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” is employed in the examples described later.

When preparing a coprecipitation precursor, Mn is easily oxidized among Co, Ni and Mn, and it is not easy to prepare a coprecipitation precursor in which Co, Ni and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Co, Ni and Mn tends to be insufficient. In particular, in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among these, when preparing a coprecipitated carbonate precursor as in the examples described later, it is preferable to employ carbon dioxide as a gas not containing oxygen because an environment in which carbonate is more easily generated is provided. .

Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to prepare the co-precipitation precursor as a co-precipitation carbonate precursor. When it does, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. By setting the pH to 9.4 or less, the tap density can be set to 1.25 g / cm ³ or more, and high-rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by setting the pH to 8.0 or less, the stirring continuation time after completion of dropping of the raw material aqueous solution can be shortened.

  The coprecipitation precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. In the present invention, in order to obtain an active material for a lithium secondary battery having a large discharge capacity, the coprecipitation precursor is preferably a carbonate. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw materials for the coprecipitation precursor include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate, and the like can be given as examples.

  In the present invention, a reaction crystallization method is employed in which a raw material aqueous solution of the coprecipitation precursor is supplied dropwise to a reaction tank maintaining alkalinity to obtain a coprecipitation carbonate precursor. Here, a sodium compound such as sodium carbonate is used as the neutralizing agent, but it is preferable to use sodium carbonate or a mixture of sodium carbonate and lithium carbonate. In order to leave Na at least 1000 ppm, Na / Li, which is the molar ratio of sodium carbonate to lithium carbonate, is preferably 1/1 [M] or more. By setting Na / Li to 1/1 [M] or more, it is possible to reduce the possibility that Na is excessively removed in the subsequent washing step and becomes less than 1000 ppm.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. In particular, Mn is difficult to form a uniform element distribution with Co and Ni, so care must be taken. The preferred dropping rate is influenced by the reaction vessel size, 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.

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles grow concentrically in stages while colliding with each other. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. 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 dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced 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 is not sufficient due to the particle size becoming too large, it is preferably 15 h or less, more preferably 10 h or less, and most preferably 5 h or less.

  Moreover, the preferable stirring duration time for setting D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles of the carbonate precursor and the lithium transition metal composite oxide is 50%, to 5 to 10 μm is controlled by pH It depends on. For example, when the pH is controlled to 8.3 to 8.9, the stirring duration is preferably 3 to 7 h, and when the pH is controlled to 7.5 to 8.0, the stirring duration is 1 to 1. 5h is preferred.

  When the carbonate precursor particles are prepared using a sodium compound such as sodium carbonate as a neutralizing agent, sodium ions adhering to the particles are washed away in the subsequent washing step. It is preferable to wash and remove under conditions such that Na remains at 1000 ppm or more. For example, when the produced carbonate precursor is removed by suction filtration, a condition that the number of washings with 200 ml of ion-exchanged water is 5 times can be employed.

The carbonate precursor is preferably dried at 80 ° C. to less than 100 ° C. in an air atmosphere under normal pressure. By drying at 100 ° C. or higher, more water can be removed in a short time, but by drying at 80 ° C. for a long time, an active material having more excellent electrode characteristics can be obtained. Although the reason is not necessarily clear, since the carbonate precursor is a porous body having a specific surface area of 50 to 100 m ² / g, it has a structure that easily adsorbs moisture. Therefore, by drying at a low temperature, a state in which a certain amount of adsorbed water remains in the pores in the state of the precursor is removed from the pores in the firing step of mixing with the Li salt and firing. The invention may be because molten Li can enter the pores so as to replace the adsorbed water, and thereby, an active material having a more uniform composition can be obtained compared with the case of drying at 100 ° C. Have guessed. In addition, although the carbonate precursor obtained by drying at 100 ° C. exhibits a black brown color, the carbonate precursor obtained by drying at 80 ° C. has a skin color, so the precursor Can be distinguished by the color.

Therefore, in order to quantitatively evaluate the difference in the precursors found above, the hues of the respective precursors are measured, and standard colors for paints (JPMA Standard Paint Colors) issued by the Japan Paint Manufacturers Association in accordance with JIS Z 8721. ) Compared with the 2011 F version. For measuring the hue, a color reader CR10 manufactured by Konica Minolta Co., Ltd. was used. According to this measuring method, the value of dL * representing lightness is larger in white and smaller in black. Further, the value of da * representing the hue is larger when red is stronger and smaller when green is stronger (red is weaker). In addition, the value of db * representing the hue becomes larger when yellow is stronger and larger when blue is stronger (yellow is weaker).
The hue of the 100 ° C. dried product (Comparative Example) is in the range reaching the standard color F05-40D in the red direction compared to the standard color F05-20B, and in the white direction compared to the standard color FN-10. It was found to be within the range leading to the standard color FN-25. Among these, it was recognized that the color difference from the hue exhibited by the standard color F05-20B was the smallest.
On the other hand, the hue of the 80 ° C. dried product (Example) is in the range reaching the standard color F19-70F in the white direction as compared with the standard color F19-50F, and is black compared with the standard color F09-80D. It was found that it was in the range reaching the standard color F09-60H in the direction. Especially, it was recognized that the color difference with the hue which standard color F19-50F exhibits is the smallest.
From the above knowledge, the hue of the carbonate precursor is preferably positive in all of dL, da and db as compared with the standard color F05-20B, dL is +5 or more, da is +2 or more, and db is It can be said that +5 or more is more preferable.
By setting the hue range of such a precursor, the synthesized positive electrode active material comes to have a larger discharge capacity.

  The positive electrode active material used for the lithium secondary battery of the present invention can be suitably prepared by mixing the carbonate precursor and the Li compound and then heat-treating them. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

  In the present invention, in order to set the content of Na in the lithium transition metal composite oxide to 3000 ppm or more, it is preferable to mix the Na compound together with the carbonate precursor together with the Li compound in the firing step. As the Na compound, sodium carbonate is preferable. Although the content of Na in the carbonate precursor is about 1000 to 2100 ppm, the content of Na can be increased to 3000 ppm or more by mixing the Na compound.

The firing temperature affects the reversible capacity of the positive electrode active material.
When the firing temperature is too high, the obtained positive electrode active material collapses with an oxygen releasing reaction, and in addition to the main phase hexagonal crystal, monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type There is a tendency that the phase defined in is observed as a phase separation rather than as a solid solution phase. Too much phase separation is not preferable because it leads to a reduction in reversible capacity of the positive electrode active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, it is preferable that the firing temperature be lower than the temperature at which the oxygen release reaction of the positive electrode active material affects. The oxygen release temperature of the positive electrode active material is approximately 1000 ° C. or higher in the composition range according to the present invention, but there is a slight difference in the oxygen release temperature depending on the composition of the positive electrode active material. It is preferable to check the temperature. In particular, it is confirmed that the oxygen release temperature of the precursor shifts to the lower temperature side as the amount of Co contained in the sample increases. As a method for confirming the oxygen release temperature of the positive electrode active material, a mixture of a coprecipitation precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. However, in this method, platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged, so a crystallization temperature is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. The composition may be subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present invention, the firing temperature is preferably at least 700 ° C. or higher. By sufficiently crystallizing, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
In addition, the inventors have analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the sample synthesized at a temperature up to 750 ° C., strain remains in the lattice, and at a temperature higher than that, It was confirmed that almost all strains could be removed by synthesis. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. all right. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process. That is, an active material having a remarkably large reversible capacity can be obtained only by selecting the firing temperature as close as possible to the oxygen release temperature of the active material.

  As described above, since the preferable firing temperature varies depending on the oxygen release temperature of the positive electrode active material, it is difficult to generally set a preferable range of the firing temperature, but the molar ratio Li / Me is 1.2 to 1.6. In some cases, the firing temperature is preferably more than 700 ° C. and not more than 950 ° C. in order to make the discharge capacity sufficient. Especially when Li / Me is 1.25 to 1.4, the firing temperature is around 800 to 900 ° C. More preferred.

In order for the positive electrode active material used in the lithium secondary battery of the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is other than a transition metal site having a layered rock salt type crystal structure. It is preferable that the ratio existing in the portion is small. This is because, in the precursor to be subjected to the firing step, the transition metal elements such as Co, Ni, and Mn in the precursor core particles are sufficiently uniformly distributed, and appropriate for promoting the crystallization of the active material sample. This can be achieved by selecting the conditions for the firing process. If the distribution of the transition metal in the precursor core particles subjected to the firing step is not uniform, a sufficient discharge capacity cannot be obtained. Although the reason for this is not necessarily clear, when the distribution of the transition metal in the precursor core particles to be subjected to the firing step is not uniform, the resulting lithium transition metal composite oxide has a layered rock salt type crystal structure other than the transition metal site. The present inventors speculate that this is due to the occurrence of so-called cation mixing, in which a part of the transition metal element is present at the lithium site. The same inference can be applied to the crystallization process in the firing step. If the crystallization of the active material sample is insufficient, cation mixing in the layered rock salt type crystal structure is likely to occur. When the distribution uniformity of the transition metal element is high, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane when the X-ray diffraction measurement result belongs to the space group R3-m is large. Tend. In the present invention, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane by X-ray diffraction measurement is preferably I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.0. Further, it is preferable that I ₍₀₀₃₎ / I ₍₁₀₄₎ > 1 in the state after the discharge after charging and discharging. If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.

In the present invention, the lithium transition metal composite oxide synthesized in order to allow at least one kind of different element selected from Al, Zr, and Ti to exist on the particle surface of the lithium transition metal composite oxide synthesized as described above. It is possible to employ a method in which the particles of the product are put into an aqueous solution of a compound (sulfate, nitrate, acetate, etc.) containing at least one different element selected from Al, Zr and Ti. This aqueous solution is preferably acidic. However, the order of input is not limited to this. For example, a method of introducing an aqueous solution of a compound containing a different element into lithium transition metal composite oxide particles dispersed in water may be employed. Further, a pH adjusting agent may be added after or when the lithium transition composite oxide is added to an aqueous solution containing a different element. The pH adjuster is not limited as long as it is an alkaline solution. Examples of the alkaline solution include an aqueous NaOH solution and an aqueous KOH solution. The pH value adjusted by adding the pH adjusting agent can be appropriately selected.
The particles to which the compound of the different element is added are separated by filtration or the like, and the obtained particles are preferably dried at 80 to 120 ° C., and further heat treated in the atmosphere at 300 to 500 ° C. for 1 to 10 hours. By performing the step, lithium transition metal composite oxide particles in which an oxide containing at least one kind of different element selected from Al, Zr and Ti is present on the particle surface can be obtained.

In the present invention, a carbon material capable of occluding and releasing lithium ions is used as the negative electrode active material. Here, the carbon material is preferably made of a mixture of graphite and amorphous carbon.
Although the negative electrode made of amorphous carbon has a smaller discharge capacity than the negative electrode made of graphite, it has a great effect of suppressing Li precipitation during charging. Therefore, by mixing amorphous carbon with graphite to form a negative electrode active material, it is possible to charge by deepening the utilization rate of the negative electrode in the high potential formation in the initial charge / discharge process. That is, the discharge capacity of the negative electrode can be further increased by inserting Li ^+, which is the difference in positive electrode capacity between high potential formation and practical use, into amorphous carbon.
In addition, by mixing amorphous carbon with graphite to form a negative electrode active material, it is possible to cut a low SOC region with high resistance, which is a weak point of a “lithium-excess type” positive electrode active material, and to improve low SOC output. There is.
In order to increase the battery capacity and improve the low SOC output, the ratio of the amorphous carbon contained in the carbon material is preferably 5 to 60% by mass. In order to further increase the battery capacity and improve the low SOC output, the ratio of the amorphous carbon contained in the carbon material is more preferably 10 to 50% by mass, and particularly preferably 10 to 30% by mass. preferable. Moreover, since initial efficiency improves by making the ratio of the said amorphous carbon 60 mass% or less to 50 mass% or less, and also 30 mass% or less, this range is preferable.

  The powder of the positive electrode active material and the negative electrode active material preferably has 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 lithium secondary battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. 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 or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  As described above, the positive electrode active material and the negative electrode active material which are main components of the positive electrode and the negative electrode have been described in detail. In addition to the main component, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, A filler etc. may be contained as another structural component.

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

  Among these, as the conductive agent, acetylene black is preferable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, acetylene black is preferably used after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. In order to sufficiently mix the conductive agent with the positive electrode active material, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like can be used in a dry or wet manner. .

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder 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 does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained liquid mixture is applied on a current collector described in detail below, or pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. . About the application method, for example, it is preferable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  The non-aqueous solvent used for the non-aqueous electrolyte used in the lithium secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethylmethyl carbonate Chain esters such as methyl formate, methyl acetate, and methyl butyrate; Tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl Examples thereof include, but are not limited to, ethers such as diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or a derivative thereof alone or a mixture of two or more thereof. .

  The lithium secondary battery according to the present invention is characterized in that fluoroethylene carbonate (FEC) is contained in a nonaqueous electrolytic solution using a nonaqueous solvent as described above. The preferable content of FEC in the non-aqueous electrolyte is 5 to 10% by volume, and more preferably 5 to 7.5% by volume.

  Non-aqueous electrolytes include 1,3-propene sultone, diglycol sulfate, 1,3-propane sultone (PS), 1,4-butane sultone, 2,4-butane sultone, sulfolane, ethylene glycol cyclic sulfate, propylene By adding a sulfur-containing compound such as glycol cyclic sulfate, sulfur (S) can be present on the negative electrode. The addition amount of the sulfur-containing compound in the nonaqueous electrolytic solution is preferably 0.5 to 2% by mass. It is presumed that a film containing S is formed on the negative electrode by reducing and decomposing these additives on the negative electrode during the first charge.

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, Inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K) such as NaBr, KClO ₄ , KSCN, 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 , (nC 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-phthalate, Examples thereof include organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzene sulfonate. These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by mixing and using 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. Low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more preferable.

  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 obtain a lithium secondary battery having high battery characteristics. 2.5 mol / l.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the lithium secondary battery separator include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride Down - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

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

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is preferable to use a separator in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction by irradiation with an electron beam (EB) or heating or ultraviolet (UV) irradiation with a radical initiator added.

  Other battery components include a terminal, an insulating plate, a battery case, and the like, but these components may be used as they are.

  FIG. 1 shows an external perspective view of a rectangular lithium secondary battery 1 which is an embodiment of a lithium secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the lithium secondary battery 1 shown in FIG. 1, an electrode group 2 is housed in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via 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 ′.

  The shape of the lithium secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device in which a plurality of the lithium secondary batteries are assembled. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of lithium secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

Example 1
(Preparation of positive electrode active material)
<Preparation of lithium transition metal composite oxide>
7.04 g of cobalt sulfate heptahydrate, 10.53 g of nickel sulfate hexahydrate and 32.60 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 1.0 M aqueous sulfate solution having a molar ratio of 12.5: 20.0: 67.5 was prepared. On the other hand, 750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropwise addition, an aqueous solution containing 1.0 M sodium carbonate and 0.2 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 8.0 (± 0.05). ) Was controlled. After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After stopping the stirring, the mixture was allowed to stand for 12 hours or more.

  Next, using a suction filtration device, the coprecipitated carbonate particles generated in the reaction vessel are separated, and further, washing is performed 5 times when 200 ml is washed once with ion-exchanged water. Sodium ions adhering to the particles under conditions were washed and removed appropriately, and dried in an air atmosphere at 80 ° C. in an air atmosphere using an electric furnace. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

5.110 g of lithium carbonate is added to 11.140 g of the coprecipitated carbonate precursor, mixed well using a smoked automatic mortar, and the molar ratio of Li: (Co, Ni, Mn) is 140: 100 A powder was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 5 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), and heated from ambient temperature to normal temperature to 890 ° C. over 10 hours in an air atmosphere. Baked at 890 ° C. for 4 h. The box-type electric furnace has internal dimensions of 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 turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After a day and night, after confirming that the furnace temperature is 100 ° C. or less, the pellets are taken out, and pulverized in a smoked automatic mortar for several minutes in order to make the particle size uniform, and the lithium transition metal composite oxide Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 O ₂ was produced. This lithium transition metal composite oxide was confirmed to have an α-NaFeO ₂ structure by X-ray diffraction measurement.

<Addition of different elements to lithium transition metal composite oxide>
Next, 5 g of the lithium transition metal composite oxide prepared as described above was put into 200 ml of a 0.1 M aqueous solution of aluminum sulfate, and stirred at 25 ° C. and 400 rpm for 30 seconds using a magnetic stirrer. Then, it separated into the powder and the filtrate by suction filtration. The pH of the filtrate was measured and found to be 2.3. The obtained powder was dried in air at 80 ° C. for 20 hours. Further, heat treatment was performed in the atmosphere for 4 hours at 400 ° C. using the above-described box-type electric furnace. Thus, the lithium transition metal composite oxide in which the Al oxide according to the positive electrode active material of Example 1 was present on the particle surface was produced.

(Measurement of particle diameter)
The lithium transition metal composite oxide according to Example 1 was subjected to particle size distribution measurement according to the following conditions and procedures. Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as a measuring device. The measurement apparatus includes an optical bench, a sample supply unit, and a computer equipped with control software. A wet cell having a laser light transmission window is installed on the optical bench. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in a sample supply unit and circulated and supplied to a wet cell by a pump. The sample supply unit is always subjected to ultrasonic vibration. In this measurement, water was used as a dispersion solvent. Moreover, Microtrac DHS for Win98 (MT3000) was used for the measurement control software. For the “substance information” to be set and input to the measuring apparatus, 1.33 is set as the “refractive index” of the solvent, “TRANSPARENT” is selected as the “transparency”, and “non-spherical” is selected as the “spherical particle”. Was selected. Prior to sample measurement, perform “Set Zero” operation. The “Set zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, dirt on the glass wall, glass irregularities, etc.) on subsequent measurements. A background operation is performed in a state where only certain water is added and only water as a dispersion solvent is circulating in the wet cell, and the background data is stored in the computer. Next, perform the “Sample LD (Sample Loading)” operation. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion that is circulated and supplied to the wet cell during measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instructions of the measurement control software. It is an operation to throw up. Subsequently, the measurement operation is performed by pressing the “Measure” button. The measurement operation is repeated twice, and the measurement result is output from the computer as the average value. The measurement results are as a particle size distribution histogram and values of D10, D50, and D90 (D10, D50, and D90 are particle sizes at which the cumulative volume in the particle size distribution of the secondary particles is 10%, 50%, and 90%, respectively) To be acquired. The measured D50 value was 8 μm.

(Measurement of pore volume distribution)
The lithium transition metal composite oxide according to Example 1 was measured for pore volume distribution according to the following conditions and procedures. For measurement of pore volume distribution, “autosorb iQ” manufactured by Quantachrome and control / analysis software “ASiQwin” were used. 1.00 g of the lithium transition metal composite oxide, which is the sample to be measured, was placed in a sample tube for measurement and vacuum-dried at 120 ° C. for 12 hours to sufficiently remove moisture in the measurement sample. Next, the adsorption side and desorption side isotherms were measured by a nitrogen gas adsorption method using liquid nitrogen within a relative pressure P / P0 (P0 = about 770 mmHg) range of 0 to 1. Then, the pore distribution was evaluated by calculating by the BJH method using the isotherm on the desorption side. This lithium transition metal composite oxide has a differential pore volume in the range of 30 to 40 nm where the differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method is the maximum, and the peak differential pore The volume value was 1.05 mm ³ / (g · nm).

(Measurement of abundance of different elements)
The presence of Al on the particle surface of the lithium transition metal composite oxide and the abundance of the Al (foreign element) were measured as follows.
A positive electrode active material containing a different element was added to 35 wt% hydrochloric acid and dissolved by boiling at 150 ° C. for 10 minutes. The obtained solution was subjected to ICP emission spectroscopic analysis to quantify the different elements.
In all Examples and Comparative Examples except Comparative Example 6 and Comparative Example 8, the amount of the different element was 0.3% by mass in terms of metal or B.

(Preparation of positive electrode)
A lithium secondary battery was produced by the following procedure using the lithium transition metal composite oxide in which Al produced on the particle surface was produced as described above as a positive electrode active material for a lithium secondary battery.
Using N-methylpyrrolidone as a dispersion medium, a coating paste in which a 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 side of an aluminum foil current collector with a thickness of 20 μm and dried to prepare a positive electrode plate. In addition, the mass of the active material applied per unit area was set to 5 mg / cm ² . Moreover, it pressed so that the porosity of an electrode might be 35% using a roll press.

(Preparation of negative electrode)
Coating in which N-methylpyrrolidone is used as a dispersion medium and an active material obtained by mixing graphitic carbon and amorphous carbon in a mass ratio of 90:10 and polyvinylidene fluoride (PVdF) are kneaded and dispersed in a mass ratio of 94: 6. A paste was prepared. The coating paste was applied to one side of a 20 μm thick copper foil current collector and dried to prepare a negative electrode plate.
TIMCAL SFG15 was used for the graphitic carbon as the negative electrode active material, and Kureha Carbotron P (hard carbon) was used for the amorphous carbon.
The mass of the active material applied per unit area was 4 mg / cm ² . Moreover, it pressed so that the porosity of an electrode might be 35% using a roll press.

(Preparation of non-aqueous electrolyte)
Fluoroethylene carbonate C ₃ H ₃ FO ₃ (FEC) was added to ethyl methyl carbonate (EMC) to prepare a mixed solvent containing EMC and FEC in a volume ratio of 95: 5. LiPF ₆ was dissolved in the mixed solvent so as to have a concentration of 1 mol / l. 2 mass% of 1, 3- propene sultone (PRS) was further added with respect to the mass of this solution, and the non-aqueous electrolyte of the lithium secondary battery which concerns on Example 1 was produced.

(Assembly of lithium secondary battery)
As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the outer package, and the open ends of the positive terminal and the negative terminal are exposed to the outside The metal resin composite film is hermetically sealed except for the portion that becomes the injection hole, and the non-aqueous electrolyte is injected, and then the injection hole Was sealed.

(Initial charge / discharge process)
The lithium secondary battery produced by the above procedure was subjected to an initial charge / discharge process at an environmental temperature of 25 ° C. Charging was performed at a constant current and a constant voltage with a current of 0.1 CmA and a voltage of 4.6 V, and the charge termination condition was when the current value 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 charge / discharge was performed for two cycles. Here, a pause process of 30 minutes was provided after charging and after discharging, respectively. In this way, a lithium secondary battery according to Example 1 was produced.

(Example 2)
According to Example 2, except that 2% by mass of diglycol sulfate (DGLST) was added in place of 1,3-propene sultone (PRS) in the non-aqueous electrolyte preparation process A lithium secondary battery was produced.

(Example 3)
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M zirconium sulfate aqueous solution, and the Zr oxide is present on the particle surface. A lithium secondary battery according to Example 3 was produced in the same manner as Example 1 except that the oxide was produced.

Example 4
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M titanium sulfate aqueous solution, and the lithium transition metal composite in which Ti oxide is present on the particle surface. A lithium secondary battery according to Example 4 was produced in the same manner as in Example 1 except that the oxide was produced.

(Comparative Example 1)
A lithium secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that 1,3-propene sultone (PRS) was not added in the production process of the nonaqueous electrolytic solution.

(Comparative Example 2)
A lithium secondary battery according to Comparative Example 2 was produced in the same manner as in Example 1 except that fluoroethylene carbonate (FEC) was not added in the production process of the nonaqueous electrolytic solution.

(Comparative Example 3)
A lithium secondary battery according to Comparative Example 3 was produced in the same manner as in Example 1 except that fluoroethylene carbonate (FEC) and 1,3-propene sultone (PRS) were not added in the non-aqueous electrolyte production process. did.

(Comparative Example 4)
A lithium secondary battery according to Comparative Example 4 was produced in the same manner as in Example 2 except that fluoroethylene carbonate (FEC) was not added in the production process of the nonaqueous electrolytic solution.

(Comparative Example 5)
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of 0.1 M boric acid aqueous solution, and the B transition oxide is present on the particle surface. A lithium secondary battery according to Comparative Example 5 was produced in the same manner as in Example 1 except that the oxide was produced.

(Comparative Example 6)
A lithium secondary battery according to Comparative Example 6 was produced in the same manner as in Example 1 except that the step of adding a different element to the lithium transition metal composite oxide was not provided.

(Comparative Example 7)
LiMeO ₂ type lithium produced by the following method instead of lithium transition metal composite oxide Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 O ₂ produced in the production process of lithium transition metal composite oxide A lithium secondary battery according to Comparative Example 7 was produced in the same manner as in Example 1 except that the transition metal composite oxide LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used.
18.77 g of cobalt sulfate heptahydrate, 17.56 g of nickel sulfate hexahydrate and 16.10 g of manganese sulfate pentahydrate were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 1.0 M aqueous sulfate solution with a molar ratio of 1: 1: 1 was prepared. On the other hand, 750 ml of ion-exchanged water was poured into a 2 L reaction vessel, and Ar gas was bubbled for 30 minutes to expel dissolved oxygen in the ion-exchanged water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropping, an aqueous solution containing 2.0 M sodium hydroxide and 0.5 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 11.0 (± 0.00. 05). After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After stopping the stirring, the mixture was allowed to stand for 12 hours or more.

(Comparative Example 8)
A lithium secondary battery according to Comparative Example 8 was produced in the same manner as Comparative Example 7, except that the step of adding a different element to the lithium transition metal composite oxide was not provided.

(Comparative Example 9)
A lithium secondary battery according to Comparative Example 9 was produced in the same manner as Comparative Example 7 except that 1,3-propene sultone (PRS) was not added in the non-aqueous electrolyte production process.

(Comparative Example 10)
A lithium secondary battery according to Comparative Example 10 was produced in the same manner as Comparative Example 7 except that fluoroethylene carbonate (FEC) was not added in the production process of the nonaqueous electrolytic solution.

(Comparative Example 11)
A lithium secondary battery according to Comparative Example 11 is manufactured in the same manner as Comparative Example 7, except that fluoroethylene carbonate (FEC) and 1,3-propene sultone (PRS) are not added in the non-aqueous electrolyte manufacturing process. did.

(Example 5)
In the step of preparing a lithium transition metal composite oxide, 2.354 g of lithium carbonate is added to 5.763 g of the coprecipitated carbonate precursor, and the molar ratio of Li: (Co, Ni, Mn) is 125: 100. A mixed active material according to Example 5 was produced in the same manner as in Example 1 _except that powder was prepared and Li _1.11 Co _0.11 Ni _0.18 Mn _0.60 O ₂ was produced.

(Example 6)
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M zirconium sulfate aqueous solution, and the Zr oxide is present on the particle surface. A lithium secondary battery according to Example 6 was produced in the same manner as Example 5 except that the oxide was produced.

(Example 7)
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M titanium sulfate aqueous solution, and the lithium transition metal composite in which Ti oxide is present on the particle surface. A lithium secondary battery according to Example 7 was produced in the same manner as Example 5 except that the oxide was produced.

(Example 8)
In the production process of the lithium transition metal composite oxide, 2.424 g of lithium carbonate is added to 5.696 g of the coprecipitated carbonate precursor, and the molar ratio of Li: (Co, Ni, Mn) is 130: 100. A mixed active material according to Example 8 was produced in the same manner as in Example 1 _except that powder was prepared and Li _1.13 Co _0.11 Ni _0.17 Mn _0.59 O ₂ was produced.

Example 9
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M zirconium sulfate aqueous solution, and the Zr oxide is present on the particle surface. A lithium secondary battery according to Example 9 was produced in the same manner as in Example 8, except that the oxide was produced.

(Example 10)
In the step of adding a different element to the lithium transition metal composite oxide, 5 g of the lithium transition metal composite oxide is added to 200 ml of a 0.1 M titanium sulfate aqueous solution, and the lithium transition metal composite in which Ti oxide is present on the particle surface. A lithium secondary battery according to Example 10 was produced in the same manner as Example 8 except that the oxide was produced.

(Examples 11-14)
In the non-aqueous electrolyte preparation process, 1,3-propane sultone (PS), sulfolane (SL), 1,4-butane sultone, and ethylene glycol cyclic sulfate were used instead of 1,3-propene sultone (PRS), respectively. Except for the addition, lithium secondary batteries according to Examples 11 to 14 were fabricated in the same manner as Example 1.

(Confirmation of the presence of S on the negative electrode)
About the produced lithium secondary battery of Examples 1-14 and Comparative Examples 1-11, it was confirmed by the following measurements that S existed or did not exist on a negative electrode. The discharged battery was disassembled and the negative electrode plate was taken out. Cleaning was performed using dimethyl carbonate for the purpose of removing LiPF ₆ , and the cleaned negative electrode plate was set in an X-ray photoelectron spectroscopy (XPS) apparatus (manufactured by SHIMADZU, AXIS-Nova). The presence of S (S-based compound) was confirmed by the presence of a peak between 163 and 169 eV in the spectrum obtained by measurement according to a conventional method.

(Discharge capacity)
About the produced lithium secondary battery of Examples 1-14 and Comparative Examples 1-11, 3 cycles charge / discharge was performed at environmental temperature 25 degreeC. Voltage control was performed between the positive and negative terminals of the battery. For the first cycle and the second cycle, the charging was performed at a constant voltage with a current of 0.1 CmA and a voltage of 4.5 V, and the charge termination condition was when the current value decreased to 0.02 CmA. After a pause of 10 minutes, the discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. For the third cycle, charging was performed at a constant voltage with a current of 0.1 CmA and a voltage of 4.35 V, and the charge termination condition was when the current value decreased to 0.02 CmA. After a pause of 10 minutes, the discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. The discharge capacity at the third cycle was recorded as “0.1 C capacity (mAh)”.

(Cycle capacity maintenance rate)
Further, after a pause of 10 minutes, a charge / discharge cycle test was repeatedly performed at an environmental temperature of 25 ° C. Charging was performed at a constant current and constant voltage with a current of 1.0 CmA and a voltage of 4.35 V, and the charge termination condition was when the current value attenuated to 0.02 CmA. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. After charging and discharging, a pause process of 10 minutes was provided. When this series of charging / discharging processes was defined as one cycle, the ratio of the discharge electricity amount obtained at the 50th cycle to the discharge electricity amount obtained at the first cycle was recorded as “cycle capacity maintenance rate (%)”. .

(Measurement of resistance)
About the produced lithium secondary battery of Examples 1-14 and Comparative Examples 1-11, the following measurements were performed and resistance was calculated | required.
The alternating current (AC) resistance was measured about the lithium secondary battery of the discharge end state before the said charging / discharging cycle test and the discharge end state after 50 cycles. Specifically, measurement was performed by connecting a measurement terminal of a high-speed response contact resistance meter (AC mΩ HiTESTER 3560, manufactured by HIOKI) between the positive and negative terminals of the lithium secondary battery. The ratio of the resistance after 50 cycles to the resistance value before the charge / discharge cycle test was recorded as “resistance increase rate (%)”.

  Table 1 shows the test results for the lithium secondary batteries according to Examples 1 to 14 and Comparative Examples 1 to 11.

From Table 1, the lithium secondary battery using the lithium-excess type lithium transition metal composite oxide (molar ratio Li / Me> 1, molar ratio Mn / Me> 0.5) as the positive electrode active material, (a) particles There is at least one oxide selected from Al, Zr, and Ti on the surface, (b) it contains fluoroethylene carbonate in the non-aqueous electrolyte, and (c) sulfur exists on the carbon negative electrode (◯ mark). It can be seen that the lithium secondary batteries of Examples 1 to 14 that satisfy the three requirements have a large cycle capacity maintenance rate and a rise in resistance is suppressed.
On the other hand, the requirements of (a) and (b) are satisfied, but the requirement of (c) is not satisfied (the x mark means that sulfur is not present on the negative electrode. The same applies hereinafter) Comparative Example 1 Comparative example 3, which satisfies the requirements of (a) but does not satisfy the requirements of (b) and (c), the comparison which satisfies the requirements of (b) and (c) but does not see the requirements of (a) In the lithium secondary battery of Example 6, the cycle capacity retention rate is small, and the resistance increase is extremely large.
Further, Comparative Examples 2 and 4 that satisfy the requirements of (a) and (c) but do not satisfy the requirement of (b), and B exists on the particle surface instead of at least one selected from Al, Zr, and Ti. In the lithium secondary battery of Comparative Example 5, the increase in resistance is suppressed, but the cycle capacity retention rate is greatly reduced.

On the other hand, for the lithium secondary battery using LiMeO ₂ type lithium transition metal composite oxide as the positive electrode active material, (a) at least one oxide selected from Al, Zr, and Ti is present on the particle surface, (B) The lithium secondary battery of Comparative Example 7 that satisfies the three requirements that the non-aqueous electrolyte contains fluoroethylene carbonate and (c) sulfur exists on the carbon negative electrode is a comparison that does not satisfy the requirement of (a) Compared to the lithium secondary battery of Example 8, the cycle capacity retention rate and resistance increase are not improved. In addition, the lithium secondary batteries of Comparative Examples 7 and 8 have a high cycle capacity maintenance rate and a resistance increase is suppressed, but compared with lithium secondary batteries using a lithium-excess type lithium transition metal composite oxide. , Capacity is inferior.
Moreover, the lithium secondary battery of Comparative Example 7 is Comparative Example 9 that does not satisfy the requirement of (c), Comparative Example 10 that does not satisfy the requirement of (b), and Comparative Example that does not satisfy the requirements of (b) and (c). Compared with 11 lithium secondary batteries, the degree of improvement in cycle capacity retention and resistance increase is not large.
In view of the above, in a lithium secondary battery using a lithium-excess type lithium transition metal composite oxide (molar ratio Li / Me> 1, molar ratio Mn / Me> 0.5) as a positive electrode active material, 3) at least one oxide selected from Al, Zr, and Ti is present on the particle surface, (b) non-aqueous electrolyte contains fluoroethylene carbonate, and (c) sulfur exists on the carbon negative electrode. The effect of adopting the requirements can be said to be significant.

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

  According to the present invention, it is possible to suppress an increase in resistance associated with a cycle of a lithium secondary battery using a high capacity “lithium-excess type” positive electrode active material. Therefore, the lithium secondary battery is used for a hybrid vehicle and an electric vehicle. It is useful as a lithium secondary battery.

Claims (2)

In a lithium secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode has an α-NaFeO ₂ structure, includes Co, Ni, and Mn as transition metals Me, and has a molar ratio Li / Me> 1. A cathode active material containing at least one selected from Al, Zr, and Ti is included on the particle surface of the lithium transition metal composite oxide having a molar ratio Mn / Me> 0.5, and the anode is made of a carbon material. A lithium secondary battery comprising: a negative active material comprising: sulfur on the negative electrode; and the non-aqueous electrolyte containing fluoroethylene carbonate.   The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte contains a sulfur-containing compound.

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