JP6036168B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a water electrolyte secondary battery characterized by a positive electrode and a non-aqueous electrolyte.

Currently, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries, in particular lithium secondary batteries, are widely installed in portable terminals and the like. In these nonaqueous electrolyte secondary batteries, LiCoO ₂ is mainly used as a positive electrode active material. However, the discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g.

Further, a solid solution of LiCoO ₂ and another compound is known as a positive electrode active material for a non-aqueous electrolyte secondary battery. Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) having a α-NaFeO ₂ type crystal structure and being a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ Was announced in 2001. LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , which are examples of the solid solution, have a discharge capacity of 150 to 180 mAh / g, and are charged and discharged. Excellent cycle performance.

For the so-called “LiMeO ₂ type” active material as described above, 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. So-called “lithium-rich” active materials are known. Such a positive electrode active material 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. By using this positive electrode active material, a lithium secondary battery having a large discharge capacity can be obtained.

  On the other hand, in order to improve the characteristics of the lithium secondary battery, various additives are added to the nonaqueous electrolyte, and a cyclic sulfate compound is known as the additive (for example, Patent Document 1). To 3).

Patent Document 1 discloses “a nonaqueous electrolytic solution containing a cyclic sulfate compound represented by the following general formula (1).
(Claim 1)
According to the present invention, “a nonaqueous electrolytic solution capable of remarkably suppressing a decrease in open circuit voltage during battery storage while improving the capacity maintenance performance of the battery, and the nonaqueous electrolytic solution” Can provide a rechargeable lithium battery ”(paragraph [0037]).

Patent Document 1 states that “as the positive electrode active material constituting the positive electrode, transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO _{2 are used.} , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _x Co _(1-x) O ₂ [0 <x <1], a composite oxide composed of lithium and a transition metal such as LiFePO _4, and the like. In the examples, LiCoO ₂ or LiMnO ₂ was used as the positive electrode active material (paragraphs [0141] and [0170]), and the nonaqueous electrolyte solution described in claim 1 Cyclic sulfate compound (in which R ¹ in the general formula (I) is a group represented by the general formula (II) and R ³ is a group represented by Me, Et, or the formula (IV), R ¹ in formula (I) is And the group represented by (III), with an R ² that a H), results of the tests are listed, maintaining initial efficiency, while improving the capacity maintenance rate after high-temperature storage test, open It is shown that the voltage drop was suppressed (paragraphs [0056] to [0058], [0166], [0168], [0176], [0178] [0186], [0188], [0203], [0205]).

Patent Document 2 discloses that in a non-aqueous electrolyte battery including a negative electrode containing lithium as an active material, a positive electrode, a solute and an organic solvent, a separator and an outer can, the organic solvent is represented by the formula (1 ), And the material of the current collector used for the positive electrode and the material of the liquid contact part with the electrolyte on the positive electrode side of the outer can are valve metals or alloys thereof A non-aqueous electrolyte battery.
R1-A-R2 (1)
Wherein R1 and R2 each independently represents an aryl group or an alkyl group optionally substituted with a halogen atom, or an aryl group optionally substituted with an alkyl group or a halogen atom, or R1 and R2 Are bonded to each other to form a cyclic structure which may contain an unsaturated bond together with -A-, and A has a structure represented by any one of formulas (2) to (5))
(Claim 1)
According to this invention, it is described that “in the case of a secondary battery, a nonaqueous electrolyte battery excellent in cycle characteristics can be provided” (paragraph [0046]).

Patent Document 2 discloses that “as a specific example of a compound in which A has a structure represented by the formula (5), a chain sulfate such as...; Ethylene glycol sulfate, 1,2-propanediol sulfate. Ester, 1,3-propanediol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 2,3-butanediol sulfate, phenylethylene glycol sulfate, methylphenylethylene glycol sulfate And cyclic sulfates such as ethylphenylethylene glycol sulfate; and chain sulfates and halides of cyclic sulfates described above (paragraph [0019]), “non-aqueous electrolyte battery of the present invention. For example, lithium cobalt oxide, lithium Lithium transition metal composite oxide materials such as nickel oxide and lithium manganese oxide; transition metal oxide materials such as manganese dioxide; use of materials capable of occluding and releasing lithium such as carbonaceous materials such as fluorinated graphite Specifically, LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and their non-stoichiometric compounds, MnO ₂ , TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , P ₂ O ₅ , CrO ₃ , V ₃ O ₃ , TeO ₂ , GeO _2, etc. ”(paragraph [0032]).

In Patent Document 3, “a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator disposed between the positive electrode and the negative electrode, and represented by the following chemical formula (I): And charging the battery case with a non-aqueous electrolyte containing a cyclic sulfate, and generating a gas in the battery case by the charging, releasing the gas to the outside of the battery case, and then A method for producing a non-aqueous electrolyte secondary battery, wherein the battery case is sealed.
(Claim 1)
According to this invention, it is described that “a non-aqueous electrolyte secondary battery with high cycle characteristics and battery swelling can be provided” (paragraph [0011]).

Patent Document 3 states that “as the positive electrode active material used for the positive electrode, a composition formula Li _x MO ₂ or Li _y M ₂ O ₄ , which is a compound capable of inserting and extracting lithium (where M is a transition) It is a metal, and x and y represent numbers of 0 ≦ x ≦ 1 and 0 ≦ y ≦ 2.) A composite oxide, an oxide having a spinel structure, a metal chalcogenide having a layered structure, or the like may be used. Specific examples thereof include, for example, a lithium cobalt composite oxide such as LiCoO ₂ , a lithium manganese composite oxide such as LiMn ₂ O _4, a lithium nickel composite oxide such as LiNiO ₂ , a lithium manganese / nickel composite oxide, Lithium manganese / nickel / cobalt composite oxide, lithium titanium composite oxide, or metal oxide such as manganese dioxide, vanadium pentoxide, chromium oxide, or disulfide Tan, is used a metal sulfides such as molybdenum disulfide. May also be used as a mixture thereof. "(Paragraph [0030]) and are described in the examples, LiCoO ₂ as a positive electrode active material Use (paragraph [0040]) is shown.

WO2012 / 053644 JP-A-11-162511 JP 2006-120460 A

In Patent Document 1, a non-aqueous electrolyte containing diglycol sulfate is used for a lithium secondary battery, so that the capacity maintenance performance of the battery is improved and the open-circuit voltage is significantly reduced when the battery is charged and stored. Although it is described that it can be suppressed, it does not describe improving the charge / discharge cycle performance of the lithium secondary battery. Moreover, it is not described that a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure and containing Co, Ni, and Mn is used as the positive electrode active material.
Patent Documents 2 and 3 describe that the cycle characteristics of a non-aqueous electrolyte secondary battery can be improved by using a non-aqueous electrolyte containing a specific cyclic sulfate compound. There is no specific description about using a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure and containing Co, Ni and Mn as an active material, and diglycol sulfate is used as a cyclic sulfate compound. The use is not described.

The present invention has an α-NaFeO ₂ type crystal structure, which is not shown in the above prior art, and a positive electrode active material including a lithium transition metal composite oxide containing Co, Ni, and Mn, among which “lithium excess type” It is an object of the present invention to improve the charge / discharge cycle performance of a nonaqueous electrolyte secondary battery using a positive electrode active material as compared with a nonaqueous electrolyte containing a specific cyclic sulfonic acid compound.

In the present invention, in order to solve the above problems, the following means are adopted.
A nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure, and a composition formula Li _{1 + α} Me _1-α O ₂ (Me is Mn, A transition metal element containing Ni and Co, a positive electrode active material containing a lithium transition metal composite oxide represented by 1.0 < (1 + α) / (1-α) ≦ 1.6), and The water electrolyte is a non-aqueous electrolyte secondary battery comprising a cyclic sulfonic acid compound represented by the following general formula (1) less than 5% by mass of the total mass of the non-aqueous electrolyte.
[In General Formula (1), R ¹ and R ² represent a group bonded to each other represented by Formula (2), or one of them is represented by General Formula (3), Formula (4) or Formula ( 5) (the part of * is bonded to either R ¹ or R ² ) and the other is a hydrogen atom. R ³ is a C 1-3 alkyl group which may contain halogen. ]

In the composition formula, the lithium transition metal composite oxide preferably satisfies 1.0 <(1 + α) / (1-α) ≦ 1.50 (lithium excess type), and 1.25 ≦ (1 + α) / It is more preferable that (1-α) ≦ 1.45.

  The non-aqueous electrolyte preferably contains less than 5% by mass of the cyclic sulfonic acid compound based on the total mass of the non-aqueous electrolyte, and preferably 0.01% by mass or more.

According to the present invention, a positive electrode active material having an α-NaFeO ₂ type crystal structure and containing a lithium transition metal composite oxide containing Co, Ni and Mn, in particular, a non-lithium-based positive electrode active material is used. By using a non-aqueous electrolyte containing the above cyclic sulfonic acid compound for the water electrolyte secondary battery, there is an effect that the charge / discharge cycle performance is remarkably improved.

It is a schematic sectional drawing of the square lithium secondary battery used for the Example of this invention.

The lithium transition metal composite oxide contained in the positive electrode active material used in the nonaqueous electrolyte secondary battery according to the present invention has an α-NaFeO ₂ type crystal structure, and includes a transition metal element Me containing Co, Ni, and Mn, and , Li, and can be expressed as Li _{1 + α} Me _1-α O ₂ (1.0 ≦ (1 + α) / (1-α) ≦ 1.6). By using a non-aqueous electrolyte containing the cyclic sulfonic acid compound represented by the above general formula (1) for a non-aqueous electrolyte secondary battery using this lithium transition metal composite oxide as a positive electrode active material, a charge / discharge cycle is achieved. There is an effect that the performance is improved.
On the other hand, a non-aqueous electrolyte battery using a lithium transition metal oxide having no α-NaFeO ₂ structure, for example, LiMn ₂ O ₄ having a spinel structure as a positive electrode active material is preferable because it does not exhibit the effects of the present invention. Absent.

In the present invention, the molar ratio Li / Me of Li to the transition metal element Me represented by (1 + α) / (1-α) in the composition formula Li _{1 + α} Me _1-α O ₂ is 1 (α = 0). By making it large (excessive lithium type) and 1.5 or less, a non-aqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle performance can be obtained, so 1 <(1 + α) / (1- α) ≦ 1.5 is preferable. Among these, from the viewpoint that a nonaqueous electrolyte secondary battery having a particularly large discharge capacity and excellent charge / discharge cycle performance can be obtained, 1.25 ≦ (1 + α) / (1-α) ≦ 1.50. It is more preferable that 1.25 ≦ (1 + α) / (1−α) ≦ 1.45.
The “Li-excess type” positive electrode active material is inferior in charge / discharge cycle performance, but by using a nonaqueous electrolyte containing the cyclic sulfonic acid compound represented by the general formula (1), the charge / discharge cycle performance is remarkably increased. improves. The battery using the “LiMeO ₂ type” positive electrode active material with (1 + α) / (1−α) = 1 (α = 0) is more charge / discharge cycle performance than the battery using the “Li-excess type” positive electrode active material. However, the charge / discharge cycle performance is further improved by using a nonaqueous electrolyte containing the cyclic sulfonic acid compound represented by the general formula (1).

  Further, in the present invention, the molar ratio Co / Me of Co to the transition metal element Me is 0.00 in that a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle performance can be obtained. It is preferable to set it as 05-0.40, and it is more preferable to set it as 0.10-0.30.

  Similarly, the molar ratio Mn / Mn of the transition metal element Me is 0.44 to 0.85 in that a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent charge / discharge cycle performance can be obtained. Is preferable, and 0.48 to 0.75 is more preferable.

The lithium transition metal composite oxide used as the positive electrode active material for the non-aqueous electrolyte secondary battery according to the present invention has the general formula Li _{1 + α} (Co _a Ni _b Mn _c ) _1-α O ₂ , provided that 1 ≦ (1 + α) / (1-α) ≦ 1.6, a + b + c = 1, a> 0, b> 0, c> 0, and essentially a composite oxide composed of Li, Co, Ni, and Mn 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 contain Na, a sodium precursor such as sodium hydroxide or sodium carbonate is used as a neutralizing agent in the step of preparing a hydroxide precursor or carbonate precursor described later, and Na remains in the washing step. Alternatively, a method of adding a sodium compound such as sodium carbonate in the subsequent firing step 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 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”.

In the lithium transition metal composite oxide according to the present invention, the half width of the diffraction peak attributed to the (003) plane is 0.204 ° when the space group R3-m is used as the crystal structure model based on the X-ray diffraction pattern. It is preferably in the range of ˜0.303 °, or the half width of the diffraction peak attributed to the (104) plane is in the range of 0.266 ° to 0.424 °. By doing so, it is possible to increase the discharge capacity of the positive electrode active material and improve the high rate discharge performance. Note that the diffraction peak of 2θ = 18.6 ° ± 1 ° that appears when using the CuKα tube is 2θ = 44.1 on the (003) plane at the Miller index hkl in the space groups P3 ₁ 12 and R3-m. diffraction peak ° ± 1 ° is the space group _P3 1 12 (114) plane, are respectively indexed to the space group in R3-m (104) plane.

Moreover, it is preferable that a lithium transition metal complex oxide does not change a structure during overcharge. This can be confirmed by being observed as a single phase belonging to the space group R3-m on the X-ray diffraction diagram when electrochemically oxidized to a potential of 5.0 V (vs. Li ^/ Li ⁺ ). Thereby, the nonaqueous electrolyte secondary battery excellent in charge / discharge cycle performance can be obtained.

When the lithium transition metal composite oxide according to the present invention is prepared from a hydroxide precursor in order to improve the discharge capacity, D50, which is a particle diameter in which the cumulative volume in the particle size distribution of the secondary particles is 50%, is prepared from the hydroxide precursor. 1 to 8 μm, and in the case of producing from a carbonate precursor, it is preferably 5 to 18 μm.
Moreover, it is preferable to set D50 to 5 μm or more because unnecessary decomposition of the cyclic sulfonic acid compound in the positive electrode field can be suppressed and charge / discharge cycle performance is further improved.

BET specific surface area of the positive electrode active material according to the present invention, the initial efficiency, in order to obtain a nonaqueous electrolyte secondary battery excellent high rate discharge performance, is preferably at least ^{1m 2 / g, 2~5m 2 /} g Gayori preferable.
Further, the tap density is preferably 1.25 g / cc or more, and more preferably 1.7 g / cc or more in order to obtain a nonaqueous electrolyte secondary battery excellent in high rate discharge performance.

When the lithium transition metal composite oxide according to the present invention is produced from a carbonate precursor, the pore diameter at which the differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows the maximum value is 30. It is in the range of ˜40 nm, and the peak differential 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 nonaqueous electrolyte secondary battery with excellent initial efficiency can be obtained. Further, by setting the peak differential pore volume to 1.75 mm ³ / (g · nm) or less, in addition to the initial efficiency, a non-aqueous electrolyte secondary battery having particularly excellent discharge capacity can be obtained. The pore volume is preferably 0.85 to 1.75 mm ³ / (g · nm).

In the present invention, a nonaqueous electrolyte containing the cyclic sulfonic acid compound represented by the above general formula (1) in a nonaqueous electrolyte secondary battery using the lithium transition metal composite oxide as described above as a positive electrode active material. By using, there is an effect that the charge / discharge cycle performance is improved.
In the general formula (1), the cyclic sulfonic acid compound in which ^one of R ¹ and R ² is a group represented by the formula (4) and the other is a hydrogen atom corresponds to diglycol sulfate (DGLST), In literature 1, indicated as 4,4′-bis (2,2-dioxo-1,3,2-dioxathiolane), 1,2,3,4-di-O-sulfanyl-meso-erythritol, 1,2 : Two diastereomers of 3,4-di-O-sulfanyl-D, L-threitol are described.
The cyclic sulfonic acid compound in which R ¹ and R ² represent a group bonded to each other represented by the formula (2) is composed of two tetravalent alcohols similar to erythritol (erythritol) as a raw material and combined with sulfonic acid. Since it has a ring, it is the same compound as DGLST. A cyclic sulfonic acid compound in which either ^one of R ¹ and R ² is a group represented by the formula (5) and the other is a hydrogen atom also has two rings combined with a sulfonic acid. A compound.
The cyclic sulfonic acid compound in which either ^one of R ¹ and R ² is a group represented by the general formula (3) and the other is a hydrogen atom uses a trivalent alcohol as a raw material and has one ring. It is a compound combined with one sulfonic acid, and has the same effect as diglycol sulfate. When R ³ is a methyl group, it is 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, and when R ³ is an ethyl group, 4-ethylsulfonyloxymethyl-2, 2-dioxo-1,3,2-dioxathiolane.
Among these, diglycol sulfate having a low molecular weight is preferable because the content in the non-aqueous electrolyte is small.

The mechanism of action of the cyclic sulfonic acid compound is not always clear. Below, the estimation mechanism of the charge / discharge cycle performance improvement at the time of using the non-aqueous electrolyte containing diglycol sulfate (DGLST) is described.
A positive electrode having an α-NaFeO ₂ type crystal structure and containing a lithium transition metal composite oxide containing Mn as a positive electrode active material is eluted with Mn from the positive electrode into the electrolyte during charge and discharge, and the Mn is negative electrode A film containing Mn is formed on the negative electrode. The coating containing Mn is considered to be a cause of reducing the battery life such as cycle characteristics.
Since the reductive decomposition potential of DGLST is about 1.1 V (vs. Li ^/ Li ⁺ ) and is relatively higher than other common solvents, the first charge of the nonaqueous electrolyte secondary battery precedes other solvents. A film derived from DGLST is formed on the negative electrode. At the time of the reductive decomposition, a part containing sulfonic acid is separated, and this part is presumed to prevent formation of a film containing Mn on the negative electrode by supplementing Mn generated by dissolution from the positive electrode. The Therefore, it is considered that the life of the nonaqueous electrolyte secondary battery such as cycle characteristics is improved by including DGLST in the nonaqueous electrolyte.
In particular, in a non-aqueous electrolyte secondary battery using a positive electrode including a lithium transition metal composite oxide having a Li / Me ratio of 1.25 or more as a positive electrode active material, the amount of Mn elution from the positive electrode tends to increase. It is considered that DGLST greatly contributes to improvement of cycle characteristics.

The content of the cyclic sulfonic acid compound is preferably included to the extent that the cyclic sulfonic acid compound is detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery. Thus, when the cyclic sulfonic acid compound is contained to the extent that it is detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery, the charge / discharge cycle performance can be improved. In addition, when the non-aqueous electrolyte secondary battery is in the state after initial activation (before use, at the time of shipment), when the cyclic sulfonic acid compound is detected from the non-aqueous electrolyte, the battery is used. Is particularly preferable because the cycle characteristics can be sufficiently improved.
The amount of the cyclic sulfonic acid compound detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery is preferably 0.01% by mass or more and less than 5% by mass. If the detected cyclic sulfonic acid compound is 0.01% by mass or more, it is preferable because cycle characteristics can be sufficiently improved. Moreover, it is preferable to make the detected cyclic sulfonic acid compound less than 5% by mass because the cost of the non-aqueous electrolyte secondary battery can be suppressed while maintaining the effects of the present invention. Especially preferably, it is 0.05 mass% or more and 4 mass% or less.
Detection (qualitative and quantitative) of the cyclic sulfonic acid compound contained in the nonaqueous electrolyte can be performed by GC-MS measurement or LC-MS measurement.

  In preparing a non-aqueous electrolyte containing a cyclic sulfonic acid compound, the mixing order of the electrolyte salt, the non-aqueous solvent and the cyclic sulfonic acid compound constituting the non-aqueous electrolyte is arbitrary. In the examples described later, after dissolving an electrolyte salt in a non-aqueous solvent, a non-aqueous electrolyte containing a cyclic sulfonic acid compound is prepared by a procedure of adding a cyclic sulfonic acid compound. Even if a non-aqueous electrolyte containing the prepared cyclic sulfonic acid compound is used, the effect of the present invention is exhibited. Similarly, when the nonaqueous electrolyte contains a compound other than the cyclic sulfonic acid compound, the mixing order is arbitrary.

Next, a method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention will be described.
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention basically contains a metal element (Li, Mn, Co, Ni) constituting the active material in accordance with the composition of the active material (oxide) for the purpose. It can be obtained by adjusting the raw material to be prepared and firing it. 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 producing a coprecipitated carbonate precursor, 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.

  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. When it does, it can be set to 10-14, and when it is going to produce the said coprecipitation precursor as a coprecipitation carbonate precursor, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. About a coprecipitation carbonate precursor, tap density can be made into 1.25 g / cc or more by making pH into 9.4 or less, and a 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 non-aqueous electrolyte 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 continuously supplied dropwise to a reaction tank that maintains alkalinity to obtain a coprecipitation precursor. Here, lithium compounds, sodium compounds, potassium compounds and the like can be used as the neutralizing agent, but when the coprecipitation precursor is prepared as a coprecipitation hydroxide precursor, sodium hydroxide, hydroxide It is preferable to use a mixture of sodium and lithium hydroxide, or sodium hydroxide and potassium hydroxide, and when preparing the coprecipitation precursor as a coprecipitation carbonate precursor, sodium carbonate, sodium carbonate It is preferable to use lithium carbonate or a mixture of sodium carbonate and potassium carbonate. Na / Li, which is a molar ratio of sodium carbonate (sodium hydroxide) and lithium carbonate (lithium hydroxide), or sodium carbonate (sodium hydroxide) and potassium carbonate (potassium hydroxide) in order to leave Na 1000 ppm or more It is preferable that Na / K which is the molar ratio is 1/1 [M] or more. By setting Na / Li or Na / K to 1/1 [M] or more, it is possible to reduce the possibility that Na will be excessively removed in the subsequent washing step and become 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, 30 h or less is preferable, 25 h or less is more preferable, and 20 h or less is most preferable.

  Moreover, the preferable stirring continuation time for making 50% particle diameter (D50) of lithium transition metal complex oxide produced from a coprecipitation hydroxide precursor into 1-8 micrometers, the lithium transition metal produced from a coprecipitation carbonate precursor A preferable stirring duration time for setting the 50% particle diameter (D50) of the composite oxide to 5 to 18 μm varies depending on the pH to be controlled. For example, for the coprecipitated hydroxide precursor, when the pH is controlled to 10 to 12, the stirring duration is preferably 1 to 10 h, and when the pH is controlled to 12 to 14, the stirring duration is 3 ~ 20h is preferred. For the coprecipitated carbonate precursor, when the pH is controlled to 7.5 to 8.2, the stirring duration is preferably 1 to 15 h, and when the pH is controlled to 8.3 to 9.4. The stirring duration is preferably 3 to 20 hours.

When coprecipitation precursor particles are prepared using sodium compounds such as sodium hydroxide and sodium carbonate as neutralizing agents, sodium ions adhering to the particles are washed away in the subsequent washing step. In the present invention, it is preferable to wash and remove under conditions such that Na remains at 1000 ppm or more. For example, when the produced coprecipitation precursor is taken out by suction filtration, a condition such 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 to 100 ° C. in an air atmosphere under normal pressure.

  The active material for a non-aqueous electrolyte secondary battery of the present invention can be suitably prepared by mixing the hydroxide precursor or 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 make the content of Na in the lithium transition metal composite oxide 1000 ppm or more, even if Na contained in the hydroxide precursor or carbonate precursor is 1000 ppm or less, the firing step The amount of Na contained in the active material can be set to 1000 ppm or more by mixing the Na compound together with the Li compound and the hydroxide precursor or carbonate precursor. As the Na compound, sodium carbonate is preferable.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. 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 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. In this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged. Therefore, a composition in which crystallization is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance Goods should 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, when coprecipitated hydroxide is used as a precursor, the firing temperature is preferably at least 700 ° C. or higher. When coprecipitated carbonate is used as a precursor, the firing temperature is preferably at least 800 ° C. or higher. In particular, when the precursor is a coprecipitated carbonate, the optimum firing temperature tends to be lower as the amount of Co contained in the precursor is larger. Thus, by sufficiently crystallizing the crystallites constituting the primary particles, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
The present inventors analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the case where the precursor is a coprecipitated hydroxide, in the sample synthesized at a temperature of less than 650 ° C. Strain remains in the lattice and can be remarkably removed by synthesizing at a temperature of 650 ° C. or higher, and when the precursor is a coprecipitated carbonate, the firing temperature is 750. In the sample synthesized at a temperature of less than 0 ° C., strain remained in the lattice, and it was confirmed that the strain could be remarkably removed by synthesis at a temperature of 750 ° C. or higher. 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.

As described above, the calcination temperature is related to the oxygen release temperature of the active material, but crystallization is caused by large growth of primary particles at 900 ° C. or higher without reaching the calcination temperature at which oxygen is released from the active material. The phenomenon is seen. This can be confirmed by observing the fired active material with a scanning electron microscope (SEM). The active material synthesized through a synthesis temperature exceeding 900 ° C. has primary particles growing to 0.5 μm or more, which is disadvantageous for Li ⁺ movement in the active material during the charge / discharge reaction, and charge / discharge cycle performance. , High rate discharge performance is reduced. The size of the primary particles is preferably less than 0.5 μm, and more preferably 0.3 μm or less.
Therefore, in order to improve the discharge capacity, charge / discharge cycle performance, and high rate discharge performance, when the lithium transition metal composite oxide according to the present invention of 1 ≦ molar ratio Li / Me ≦ 1.6 is used as the positive electrode active material, The firing temperature is preferably 700 to 1000 ° C. In the case of the “lithium-excess type” positive electrode active material, firing at 750 to 900 ° C. is more preferable, and in the case of the “LiMeO ₂ type” positive electrode active material, baking at 850 to 1000 ° C. is more preferable.

In order for the positive electrode active material according to the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is present in a portion other than the transition metal site of the layered rock salt type crystal structure. It is preferable that the ratio 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 I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of the (003) plane and the (104) plane measured by X-ray diffraction measurement is 1.0 or more at the end of discharge and 1.75 at the end of charge. The above is preferable. If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.

The negative electrode active material is not limited, and any negative electrode active material that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, 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, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.
However, in the present invention, it is necessary to reduce and decompose the cyclic sulfonic acid compound. Thus, if the reversible potential of using an active material such as 1V (vs.Li/Li ⁺⁾ higher than lithium titanate _{(Li 4} Ti _{5 O 12)} is once 1V (vs.Li/Li ⁺⁾ anode to below It is preferable to lower the potential.

  The positive electrode active material powder and the negative electrode active material powder preferably have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte 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.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  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 desirable 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, it is desirable to use acetylene black by pulverizing 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, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  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.

  As the filler, any material that does not adversely affect the battery performance may be used. 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 desirable 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 nonaqueous electrolyte used for the nonaqueous electrolyte 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. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the nonaqueous 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-mal _{ate, (C 2 H 5)} 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts of lithium dodecyl benzene sulfonate, and the like. These 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. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  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 reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

  For the purpose of improving the performance of the non-aqueous electrolyte secondary battery, the cyclic sulfonic acid compound and other compounds may coexist in the non-aqueous electrolyte as long as the effects of the present invention are not impaired. Examples of the compound other than the cyclic sulfonic acid compound include vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, 1,3-propene sultone, propane sultone, phosphoric acid, phosphoric acid compound, and the like. Among these, vinylene carbonate is preferable because it can suppress battery swelling of the nonaqueous electrolyte secondary battery. The amount of vinylene carbonate added is preferably 5% by mass or less in order to effectively suppress battery swelling. The amount of 1,3-propene sultone, propane sultone, phosphoric acid, and phosphoric acid compound added is preferably 2% by mass or less.

  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 separator for a nonaqueous electrolyte battery 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 - 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 desirable that the separator be used 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 using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The configuration of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery.

Both the conventional positive electrode active material and the active material of the present invention can be charged / discharged when the positive electrode potential reaches around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Therefore, even when a charging method is employed such that the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or lower during use, a sufficient discharge capacity can be obtained. Secondary batteries may be required. When the active material of the present invention is used, for example, 4.4 V (vs. Li ^/ Li) such that the maximum potential of the positive electrode during charging is lower than 4.5 V (vs. Li ^/ Li ⁺ ) during use. ⁺ ) Or less and 4.3 V (vs. Li ^/ Li ⁺ ) or less, even if a charging method is adopted, it is possible to take out a discharge electric quantity exceeding the capacity of the conventional positive electrode active material of about 200 mAh / g or more. Is possible.
By adopting the synthesis conditions and synthesis procedures described in the present specification, a high-performance positive electrode active material as described above can be obtained.

Example 1
(Preparation of “lithium-rich” cathode active material)
14.31 g of cobalt sulfate heptahydrate, 20.96 g of nickel sulfate hexahydrate and 65.12 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 2.0 M sulfate aqueous solution having a molar ratio of 12.5: 19.9: 67.4 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 dropping, an aqueous solution containing 2.0 M sodium carbonate and 0.4 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 7.9 (± 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 produced in the reaction vessel are separated, and sodium ions adhering to the particles are washed away using ion-exchanged water, and an electric furnace is used. And dried at 100 ° C. under normal pressure in an air atmosphere. 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.

Add 1.000 g of lithium carbonate to 2.278 g of the coprecipitated carbonate precursor, mix well using a smoked automatic mortar, and the molar ratio of Li: (Co, Ni, Mn) is 134: 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 2 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), heated in air atmosphere at normal pressure from room temperature to 800 ° C. over 10 hours, Baked at 800 ° 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 the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, the lithium transition metal composite oxide used in Example 1 was produced.
This was used as the “lithium-rich” positive electrode active material used in Example 1.

(Preparation of positive electrode)
The positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 90: 5: 5. This mixture was kneaded and dispersed by adding N-methylpyrrolidone as a dispersion medium to prepare a coating solution. In addition, about PVdF, it converted into solid mass by using the liquid by which solid content was melt | dissolved and dispersed. The coating solution was applied to both sides of a 15 μm thick aluminum foil current collector and dried. The positive electrode coating mass was 10.5 mg / cm ² . Next, the positive electrode plate was produced by roll pressing.

(Preparation of negative electrode)
Meanwhile, a negative electrode paste in which graphite, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as negative electrode active materials were kneaded and dispersed at a mass ratio of 97: 1: 2 using ion exchange water as a dispersion medium was prepared. . The negative electrode paste was applied to both sides of a 10 μm thick copper foil current collector and dried. The negative electrode coating mass was 14.0 mg / cm ² . Next, the negative electrode plate was produced by roll pressing.

(Preparation of non-aqueous electrolyte)
As a non-aqueous electrolyte, LiPF ₆ as an electrolyte salt is dissolved in a mixed solvent having a volume ratio of EC / EMC / DEC of 3: 2: 5 so that its concentration becomes 1 mol / l. What dissolved diglycol sulfate (DGLST) so that it might become 0.01 mass% with respect to the mass of electrolyte was used. This was used as the nonaqueous electrolyte used in Example 1.

(Preparation of prismatic nonaqueous electrolyte secondary battery)
FIG. 1 is a schematic cross-sectional view of a prismatic lithium secondary battery used in this example. This square lithium secondary battery 1 has a positive electrode plate 3 having a positive electrode mixture layer containing a positive electrode active material in an aluminum foil current collector, and a negative electrode mixture layer containing a negative electrode active material in a copper foil current collector. A power generating element including a flat wound electrode group 2 in which a negative electrode plate 4 is wound via a separator 5 and a nonaqueous electrolyte containing an electrolyte salt is formed in a battery case 6 having a width of 34 mm, a height of 50 mm, and a thickness of 5.2 mm. It is something that is stored. A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, the negative electrode plate 4 is connected to a negative electrode terminal 9 via a negative electrode lead 11, and the positive electrode plate 3 is connected to a battery via a positive electrode lead 10. Connected to the lid.
As the separator 5, a 20 μm thick polyethylene microporous membrane (Asahi Kasei H6022) was used.
A nonaqueous electrolyte secondary battery according to Example 1 was produced as described above.

(Examples 2-9)
In the nonaqueous electrolyte used in Example 1, the addition amount (mass%) of diglycol sulfate (DGLST) was 0.05%, 0.10%, 0.20%, 0.50%, 1.00%. The nonaqueous electrolyte secondary batteries according to Examples 2 to 9 were produced in the same manner as in Example 1, except that the content was 2.00%, 3.00%, and 4.00%.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same manner as in Example 1 except that diglycol sulfate (DGLST) was not added to the nonaqueous electrolyte used in Example 1.

(Comparative Example 2)
The nonaqueous electrolyte used in Example 1 was the same as Example 1 except that 0.50% by mass of vinylene carbonate (VC) was added instead of diglycol sulfate (DGLST). A water electrolyte secondary battery was produced.

(Comparative Example 3)
Comparative Example 3 is the same as Example 1 except that 0.50% by mass of pentyl glycol sulfate (PEGLST) is added in place of diglycol sulfate (DGLST) in the nonaqueous electrolyte used in Example 1. A non-aqueous electrolyte secondary battery was produced.

(Comparative Example 4)
In the same manner as in Example 1, except that 0.50% by mass of 1,3-propene sultone (PRS) was added instead of diglycol sulfate (DGLST) in the non-aqueous electrolyte used in Example 1, a comparative example A non-aqueous electrolyte secondary battery according to No. 4 was produced.

(Example 10)
Example 10 is a reference example (hereinafter the same).
(Preparation of “LiMeO ₂ type” positive electrode active material)
Manganese sulfate pentahydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate are dissolved in ion-exchanged water so that each element of Co, Ni, and Mn has a ratio of 1: 1: 1 to prepare a mixed aqueous solution. did. At that time, the total concentration was 0.667M and the volume was 180 ml. Next, 600 ml of ion-exchanged water was prepared in a 1-liter beaker, maintained at 50 ° C. using a hot water bath, and 8N NaOH was added dropwise to adjust the pH to 11.5. In this state, Ar gas was bubbled for 30 minutes to sufficiently remove dissolved oxygen in the solution. The inside of the beaker was stirred at 700 rpm, and the mixed aqueous solution of the previous sulfate was dropped at a speed of 3 ml / min. Meanwhile, the temperature was kept constant in a hot water bath, and the pH was kept constant by intermittently dropping 8N NaOH. At the same time, 50 ml of a 2.0 M hydrazine aqueous solution as a reducing agent was added dropwise at a speed of 0.83 ml / min. After both droppings were completed, the coprecipitated hydroxide was sufficiently grown by standing still for 12 hours or more with stirring stopped.
Next, the coprecipitation product was taken out by suction filtration and dried in an oven at 100 ° C. under normal pressure in an air atmosphere. After drying, the precursor was pulverized for several minutes in a mortar having a diameter of about 120 mmφ so that the particle diameters were uniformed to obtain a precursor dry powder.

The obtained precursor dry powder and lithium hydroxide monohydrate powder (LiOH.H2O) were mixed well using a smoked automatic mortar, and the molar ratio of Li: (Co, Ni, Mn) was 1: 1. A mixed powder was prepared.
Next, the mixed powder was pellet-molded at a pressure of 6 MPa. The amount of the precursor powder subjected to pellet molding was determined by conversion so that the mass as a product after synthesis was 3 g. As a result, the molded pellets had a diameter of 25 mmφ and a thickness of about 10-12 mm. The pellets were placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace, and baked in an air atmosphere at 1000 ° C. for 12 hours. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. After the passage of day and night, it was confirmed that the temperature of the furnace was 100 ° C. or less, and then the pellets were taken out and pulverized to the same particle size using a mortar. Thus, the lithium transition metal complex oxide used in Example 10 was produced.
This was used as the “LiMeO ₂ type” positive electrode active material used in Example 10.

(Preparation of prismatic nonaqueous electrolyte secondary battery)
A nonaqueous electrolyte secondary battery according to Example 10 was fabricated in the same manner as in Example 6 except that the above-described “LiMeO ₂ type” positive electrode active material was used instead of the “lithium-excess type” positive electrode active material. did.

(Comparative Example 5)
A nonaqueous electrolyte secondary battery according to Comparative Example 5 was produced in the same manner as in Example 10 except that diglycol sulfate (DGLST) was not added to the nonaqueous electrolyte used in Example 10.

(Measurement of particle diameter)
The lithium transition metal composite oxides used in Examples 1 to 9 and Comparative Examples 1 to 4 were measured for particle size distribution 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 value of D50 obtained was 18 μm.

(Measurement of specific surface area)
The lithium transition metal composite oxides used in Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to nitrogen adsorption on the active material by a single-point method using a specific surface area measuring device (trade name: MONOSORB) manufactured by Yuasa Ionics. The amount [m ² ] was determined. A value obtained by dividing the obtained adsorption amount (m ² ) by the active material mass (g) was defined as a BET specific surface area. In the measurement, gas adsorption by cooling with liquid nitrogen was performed. In addition, preheating at 120 ° C. for 15 minutes was performed before cooling. The input amount of the measurement sample was 0.5 g ± 0.01 g.
The specific surface area obtained was a BET specific surface area of 5.6 m ² / g.

(Initial activation process)
The produced square nonaqueous electrolyte secondary battery was transferred to a thermostat set at 25 ° C., and an initial charge / discharge process of one cycle was performed. The charge / discharge conditions are as follows.
<Battery Using “Lithium Excess Type” Positive Electrode Active Material> Examples 1 to 9 and Comparative Examples 1 to 4
The charging was constant current and constant voltage charging with a current of 0.2 CmA, a voltage of 4.5 V, and a charging time of 8 hours. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. A 30 minute rest period was set after charging and discharging.
<Battery Using “LiMeO ₂ Type” Cathode Active Material> Example 10 and Comparative Example 5
The charging was constant current and constant voltage charging with a current of 0.2 CmA, a voltage of 4.2 V, and a charging time of 8 hours. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.75V. A 30 minute rest period was set after charging and discharging.

(Capacity confirmation test)
After the initial activation step, a capacity confirmation test was subsequently performed. The charge / discharge conditions are described below.
<Battery Using “Lithium Excess Type” Positive Electrode Active Material> Examples 1 to 9 and Comparative Examples 1 to 4
The charging was constant current and constant voltage charging with a current of 0.2 CmA, a voltage of 4.2 V, and a charging time of 8 hours. The discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.0 V. In addition, a pause time of 30 minutes was set after charging and discharging.
<Battery Using “LiMeO ₂ Type” Cathode Active Material> Example 10 and Comparative Example 5
The charging was constant current and constant voltage charging with a current of 0.2 CmA, a voltage of 4.2 V, and a charging time of 8 hours. The discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V. In addition, a pause time of 30 minutes was set after charging and discharging.
The discharge capacity of each battery obtained in the above discharge process is shown in Table 1 as “1C discharge capacity”.
Further, the results of measuring the battery thickness after the discharge of each battery are also shown in Table 1.

(Battery thickness measurement)
The battery thickness was measured for each battery after the capacity check test.
After 24 hours from the end of the capacity confirmation test, the center of the long side of the battery is sandwiched with calipers from a direction substantially perpendicular to the long side (in a direction substantially horizontal to the surface of the short side), and the battery thickness is measured. did. This value is shown in Table 1 as “battery thickness before cycle (mm)”.

(Internal resistance measurement)
The 1 kHz internal resistance 24 hours after the completion of the capacity confirmation test was measured using a Hioki 3560 AC HITESTER manufactured by Hioki Electric Co., Ltd. This value is shown in Table 1 as “pre-cycle internal resistance (mΩ)”.

(45 ° C cycle test)
The square nonaqueous electrolyte secondary battery was transferred to a thermostat set at 45 ° C., and a charge / discharge cycle test of 100 cycles was performed. The charging / discharging conditions in each battery are described below.
<Battery Using “Lithium Excess Type” Positive Electrode Active Material> Examples 1 to 9 and Comparative Examples 1 to 4
Charging was performed at a constant current and a constant voltage with a current of 1.0 CmA, a voltage of 4.2 V, and a charging time of 3 hours. The discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.0 V. A 30 minute rest period was set after all charging and discharging.
<Battery Using “LiMeO ₂ Type” Cathode Active Material> Example 10 and Comparative Example 5
Charging was performed at a constant current and a constant voltage with a current of 1.0 CmA, a voltage of 4.2 V, and a charging time of 3 hours. The discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V. In addition, a pause time of 30 minutes was set after charging and discharging.
The ratio of the discharge capacity obtained in the 100th cycle to the discharge capacity obtained in the first cycle of this cycle test (“100th cycle discharge capacity” / “first cycle discharge capacity”) is expressed as “cycle capacity maintenance ratio (% ) "And shown in Table 1.

  Each battery after completion of the cycle test was transferred to a constant temperature bath at 25 ° C., and after 24 hours, the battery thickness was measured by the same method as described above. This battery thickness is defined as “battery thickness after cycle (mm)” and is shown in Table 1. Also, the ratio of “battery thickness after cycle” to “battery thickness before cycle” (“battery thickness after cycle” / “battery thickness before cycle”) is “battery thickness increase rate (%)”, which is also shown in Table 1.

  After measuring the battery thickness, the 1 kHz internal resistance of each battery was further measured. Record the obtained value as “Internal resistance after cycle (mΩ)” and calculate the ratio to “Internal resistance before cycle” (“Internal resistance after cycle” / “Internal resistance before cycle”). It is shown in Table 1 as “resistance increase rate (%)”.

(45 ° C standing test)
The batteries according to Examples 1 to 10 and Comparative Examples 1 to 5 were newly assembled, and batteries were manufactured by performing the initial activation process. About the produced battery, the capacity | capacitance confirmation test was done, and also 1 hour internal resistance measurement was carried out 24 hours after completion | finish of a capacity | capacitance confirmation test.
Next, after carrying out constant current constant voltage charging with a current of 1.0 CmA, a voltage of 4.2 V, and a charging time of 3 hours, the battery was transferred to a constant temperature bath set at 45 ° C. and left for 60 days.
The battery after being left was transferred to a thermostat set at 25 ° C., and for the batteries of Examples 1 to 9 and Comparative Examples 1 to 4, constant current discharge with a current of 1.0 CmA and a final voltage of 2.0 V, Example 10 and For the battery of Comparative Example 5, constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V was performed.
The 1 kHz internal resistance after 24 hours from the discharge was measured.
Regarding the internal resistance before and after being left, the “increase rate of internal resistance when left as it is” was calculated by the following formula. The results are shown in Table 2.
“Internal resistance increase rate when left (%)” = “Internal resistance value after being left” / “Internal resistance value before being left” × 100

From Table 1 and Table 2, the 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) in the “Li-excess type” positive electrode active material containing the lithium transition metal composite oxide represented include DGLST It can be seen that the cycle capacity retention rate (charge / discharge cycle performance) is improved and the internal resistance after the cycle and the internal resistance at the time of leaving are decreased as compared with the battery of Comparative Example 1 using the nonaqueous electrolyte. The content of DGLST is effective at 0.01% to 4.00%, more preferably 0.05% to 4.00%, and particularly preferably 0.50% to 4.00%.
In contrast, the battery of Comparative Example 2 using a non-aqueous electrolyte containing vinylene carbonate (VC) has an improved battery thickness increase rate but a reduced cycle capacity retention rate compared to the case where it is not added. However, the internal resistance becomes high. The battery of Comparative Example 3 using the non-aqueous electrolyte containing pentyl glycol sulfate (PEGLST) is inferior in all characteristics as compared with the case where it is not contained. 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 ratio is lowered, and the battery The thickness increases.
A battery using a “LiMeO ₂ type” positive electrode active material has a higher cycle capacity retention rate than a battery using a “Li-excess type” positive electrode active material, but a nonaqueous electrolyte containing DGLST is employed (Examples) 10) The cycle capacity retention rate is further improved and the internal resistance is slightly higher than that of Comparative Example 5 that employs a nonaqueous electrolyte that does not contain DGLST.

  By using a positive electrode active material containing a lithium transition metal composite oxide containing Mn, Ni and Co of the present invention and combining it with a non-aqueous electrolyte containing a specific cyclic sulfonic acid compound, charge / discharge cycle performance Therefore, this non-aqueous electrolyte secondary battery is useful as a non-aqueous electrolyte secondary battery for hybrid vehicles and electric vehicles.

Claims (4)

A nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has an α-NaFeO ₂ type crystal structure, and a composition formula Li _{1 + α} Me _1-α O ₂ (Me is Mn, A transition metal element containing Ni and Co, a positive electrode active material containing a lithium transition metal composite oxide represented by 1.0 < (1 + α) / (1-α) ≦ 1.6), and The water electrolyte contains a cyclic sulfonic acid compound represented by the following general formula (1) in an amount of less than 5% by mass of the total mass of the nonaqueous electrolyte.
[In General Formula (1), R ¹ and R ² represent a group bonded to each other represented by Formula (2), or one of them is represented by General Formula (3), Formula (4) or Formula ( 5) (the part of * is bonded to either R ¹ or R ² ) and the other is a hydrogen atom. R ³ is a C 1-3 alkyl group which may contain halogen. ] 2. The non-active material according to claim 1, comprising a positive electrode active material containing a lithium transition metal composite oxide satisfying 1.0 <(1 + α) / (1−α) ≦ 1.50 in the composition formula. Water electrolyte secondary battery.   3. The non-active material according to claim 2, comprising a positive electrode active material containing a lithium transition metal composite oxide satisfying 1.25 ≦ (1 + α) / (1−α) ≦ 1.45 in the composition formula. Water electrolyte secondary battery. The nonaqueous electrolyte secondary according to any one of claims 1 to 3 , wherein the nonaqueous electrolyte contains the cyclic sulfonic acid compound in an amount of 0.01 mass% or more of the total mass of the nonaqueous electrolyte. battery.