Active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

Provided is an active material contributing to improving the charge / discharge cycle characteristics of a battery. This active material for a non-aqueous electrolyte secondary battery includes: a core capable of reversible intercalation and deintercalation of Li; and a salt attached to the surface of the core, wherein the salt comprises an oxyfluoride represented by general formula M1OFa (2≤a≤ 6, M1 is at least one element selected from the group consisting of Ti, Zr, Si, P, and B).

Description

[Technical Field]

[0001] The present disclosure relates to an active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the active material. [Background technology]

[0002] The active material contained in a non-aqueous electrolyte secondary battery may undergo a side reaction with the electrolyte, resulting in a decrease in battery capacity due to repeated charge and discharge. Patent Document 1 discloses a surface-modified lithium-containing composite oxide in which zirconium hydroxide or zirconium oxide and at least one lithium salt selected from the group consisting of LiZrF6, LiTiF6, LiPO4, LiSO4, and LiSO4·H2O are attached to the surface of the lithium-containing composite oxide for the purpose of improving charge and discharge cycle characteristics, etc. Patent Document 1 also discloses a method for producing the surface-modified lithium-containing composite oxide, in which a powder of the lithium-containing composite oxide is mixed with a solution containing zirconium and a solution containing an ammonium salt, and the mixture is subjected to heat treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 104234 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of intensive studies by the present inventors, it has been found that depending on the mixing conditions and heat treatment conditions when producing the surface-modified lithium-containing composite oxide, it is not possible to suppress the decrease in battery capacity due to repeated charge and discharge.

[0005] Therefore, an object of the present disclosure is to provide an active material that contributes to improving the charge-discharge cycle characteristics of a battery. [Means for solving the problem]

[0006] An active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a core capable of reversibly absorbing and desorbing Li and a salt attached to the surface of the core, the salt being represented by the general formula MOF a (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B).

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including an electrode containing the above-described active material for a non-aqueous electrolyte secondary battery, a counter electrode for the electrode, and a non-aqueous electrolyte. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to suppress a decrease in battery capacity due to repeated charging and discharging. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a longitudinal cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0010] By attaching an oxide or the like to the surface of the active material, it is possible to suppress side reactions such as electrolyte decomposition and elution of transition metals from the positive electrode active material during charge and discharge of the battery. However, the battery characteristics change depending on the compound attached to the surface. After extensive research, the inventors have found that applying a compound of the general formula M1OF to the surface of the active material a They found that the charge-discharge cycle characteristics of secondary batteries can be improved by attaching a salt containing an oxyfluoride represented by the formula (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B). It is presumed that this salt specifically suppresses side reactions, thereby protecting the active material and maintaining the battery capacity even after repeated charge-discharge cycles.

[0011] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. Hereinafter, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical battery case will be exemplified. However, the electrode assembly is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators interposed therebetween. Furthermore, the battery case is not limited to a cylindrical shape and may be, for example, a prismatic or coin-shaped battery case, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0012] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in an exterior case 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the nonaqueous electrolyte include carbonates, lactones, ethers, ketones, and esters, and two or more of these solvents can be mixed. When two or more solvents are mixed, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like can be used as the chain carbonate. Examples of electrolyte salts that can be used for the non-aqueous electrolyte include LiPF, LiBF, LiCF, SO, and mixtures thereof. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L. For ease of explanation, the following description will refer to the sealing body 16 side as "top" and the bottom side of the exterior body 15 as "bottom."

[0013] The open end of the exterior body 15 is sealed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 toward the bottom of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal. Note that if the negative electrode lead 20 is installed at the terminal end, the negative electrode lead 20 passes outside the insulating plate 18, extends toward the bottom of the exterior body 15, and is welded to the inner bottom surface of the exterior body 15.

[0014] Exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between exterior body 15 and sealing body 16, ensuring the airtightness of the interior of secondary battery 10. Exterior body 15 has a grooved portion 21 that supports sealing body 16, formed, for example, by pressing the side surface from the outside. Grooved portion 21 is preferably formed in an annular shape along the circumferential direction of exterior body 15, and supports sealing body 16 on its upper surface via gasket 27.

[0015] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may break, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, and gas may be released from the opening 26a of the cap 26.

[0016] The following describes the positive electrode 11, negative electrode 12, and separator 13 that constitute the secondary battery 10. Note that, although the following describes an example in which a salt containing an oxyfluoride is applied to the active material (positive electrode active material) contained in the positive electrode 11, a salt containing an oxyfluoride may be applied to the active material (negative electrode active material) contained in the negative electrode 12, or a salt containing an oxyfluoride may be applied to both the positive electrode active material and the negative electrode active material.

[0017] [Positive electrode] The positive electrode 11 has, for example, a positive electrode core such as a metal foil and a positive electrode composite layer formed on the positive electrode core. The positive electrode core can be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a film with such a metal disposed on the surface layer. The positive electrode composite layer contains, for example, a positive electrode active material, a binder, a conductive material, etc. The positive electrode can be produced, for example, by applying a positive electrode composite slurry containing the positive electrode active material, the binder, the conductive material, etc. to the positive electrode core, drying the slurry to form a positive electrode composite layer, and then rolling the positive electrode composite layer.

[0018] Examples of conductive materials contained in the positive electrode mixture layer include carbon particles such as carbon black (CB), acetylene black (AB), ketjen black, graphite, etc. These may be used alone or in combination of two or more.

[0019] Examples of binders contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more.

[0020] The positive electrode active material contains, for example, a lithium-containing composite oxide as a core capable of reversibly absorbing and releasing Li. The lithium-containing composite oxide has a layered structure. The lithium-containing composite oxide may have, for example, a layered structure belonging to the space group R-3m or a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and stability of the crystal structure, it is preferable that the lithium-containing composite oxide has a layered structure belonging to the space group R-3m.

[0021] The lithium-containing composite oxide is, for example, a secondary particle formed by aggregation of a plurality of primary particles. The particle size of the primary particles constituting the secondary particle is, for example, 0.05 μm to 1 μm. The particle size of the primary particle is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM).

[0022] The volume-based median diameter (D50) of the secondary particles of the lithium-containing composite oxide is, for example, 1 μm to 30 μm, preferably 3 μm to 20 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the composite oxide (Z) can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrack Bell Corporation) with water as the dispersion medium.

[0023] Lithium-containing composite oxides are represented by the general formula Li x Ni y M2 1-y O2 (0.9≦x≦1.4, 0.4≦y≦1, M2 is at least one element selected from the group consisting of Mn, Co, Al, and Fe). The mole fraction of each element constituting the lithium-containing composite oxide can be measured by, for example, inductively coupled plasma (ICP) atomic emission spectrometry.

[0024] x, which indicates the proportion of Li in the lithium-containing composite oxide, preferably satisfies 0.9≦x≦1.4, and more preferably satisfies 1.1≦x≦1.4. When x<0.9, the battery capacity may be reduced compared to when x satisfies the above range. When x>1.4, the charge-discharge cycle characteristics may be reduced compared to when x satisfies the above range.

[0025] The ratio y, which indicates the ratio of Ni to the total number of moles of metal elements excluding Li in the lithium-containing composite oxide, preferably satisfies 0.4≦y≦1, and more preferably satisfies 0.7≦y≦0.95.

[0026] M2 (M2 is at least one element selected from the group consisting of Mn, Co, Al, and Fe) relative to the total number of moles of metal elements excluding Li in the lithium-containing composite oxide is an optional component, and 1-y, which indicates the ratio thereof, satisfies 0≦1-y≦0.6.

[0027] The surface of the lithium-containing composite oxide core is covered with a compound of the general formula M1OF a (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B) is attached to the secondary battery 10. This can improve the charge-discharge cycle characteristics of the secondary battery 10.

[0028] The surface of the lithium-containing composite oxide core is the surface of a secondary particle of the lithium-containing composite oxide. The salt may also be attached to the interior of the secondary particle of the lithium-containing composite oxide, i.e., to the surface of the primary particle. Having the salt attached to the surface of the primary particle as well can further improve the charge / discharge cycle characteristics of the secondary battery 10. The salt may be present in a dotted form so as to cover at least a portion of the surface of the lithium-containing composite oxide, or may be present so as to cover the entire surface of the lithium-containing composite oxide. The particle diameter of the salt is, for example, 0.1 μm to 2 μm. The particle diameter of the salt is measured as the diameter of a circumscribed circle in a particle image observed by SEM. Specifically, the outer shapes of 20 randomly selected particles are identified, and the major axis (longest diameter) of each of the 20 particles is determined, and the average value thereof is taken as the particle diameter of the salt.

[0029] General formula M1OF a In the oxyfluoride represented by the formula (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B), M1 may be Ti or Zr. Ti or Zr is preferred because a stable fluoride complex is formed.

[0030] General formula M1OF a The valence of the oxyfluoride represented by the formula (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B) is, for example, −7 to 0. The salt containing the oxyfluoride may contain a cation in addition to the oxyfluoride. Examples of the cation include ammonium ion (NH4 + ), potassium ions (K + ), sodium ions (Na + ), calcium ions (Ca 2+ ) etc.

[0031] The salt may be (NH4)2M1OF4 (M1 is at least one element selected from the group consisting of Ti, Zr, Si, and B).

[0032] The amount of salt attached to the lithium-containing composite oxide is preferably 0.01 mol % to 1 mol %, more preferably 0.05 mol % to 0.5 mol %. The presence of salt on the surface of the lithium-containing composite oxide can be confirmed by X-ray diffraction (XRD). The amount of salt attached to the lithium-containing composite oxide can also be measured by XRD.

[0033] Next, an example of a method for producing a positive electrode active material according to the present disclosure will be described. For convenience of explanation, the following describes a method for producing a positive electrode active material by forming a compound having a general formula M1OF on the surface of a lithium-containing composite oxide. a (2≦a≦6, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B) is referred to as a "composite oxide (Y)." In the present disclosure, the positive electrode active material included in the secondary battery 10 may contain the composite oxide (Y) as a main component and may be substantially composed of the composite oxide (Y) alone. Note that the positive electrode active material may contain a composite oxide other than the composite oxide (Y) or other compounds within the scope of the present disclosure.

[0034] The lithium-containing composite oxide serving as the core can be synthesized, for example, by adding a Li source to a composite compound (X) that does not contain Li, mixing the mixture, and firing at 200°C to 1050°C. Examples of the composite compound (X) include composite oxides, hydroxides, carbonates, etc. that contain Ni, Mn, etc. Examples of the Li source include LiOH, etc. The lithium-containing composite oxide is washed with water by a known method and under known conditions, and the amount of LiOH remaining on the surface of the lithium-containing composite oxide after washing varies depending on the washing conditions. The lithium-containing composite oxide after washing is dried and turned into powder. The median diameter (D50) of the lithium-containing composite oxide can be adjusted by the firing conditions, etc.

[0035] Next, the powdered lithium-containing composite oxide was treated with a compound of the general formula M1F w(4≦w≦8, M1 is one or more elements selected from the group consisting of Ti, Zr, Si, P, and B) is added and dry mixed. As a result, LiOH on the surface of the lithium-containing composite oxide reacts with the fluoride to generate a salt containing an oxyfluoride, thereby obtaining a composite oxide (Y). Examples of the salt containing fluoride include (NH4)2TiF6, (NH4)2ZrF6, (NH4)2SiF6, and NHFBF 4、 Examples include NH4PF4. The particle diameter of the fluoride-containing salt is, for example, 0.1 μm to 2 μm. The particle diameter of the fluoride-containing salt is measured as the diameter of the circumscribed circle in a particle image observed by SEM. Specifically, the outer shapes of 20 randomly selected particles are identified, and the major axis (longest diameter) of each of the 20 particles is determined, and the average value of these is taken as the particle diameter of the fluoride-containing salt.

[0036] The amount of salt added to the lithium-containing composite oxide is preferably 0.01 mol % to 1 mol %, more preferably 0.05 mol % to 0.5 mol %. Within this range, an appropriate amount of salt containing an oxyfluoride can be attached to the surface of the lithium-containing composite oxide, thereby suppressing side reactions on the surface of the lithium-containing composite oxide. For example, mechanofusion may be used for dry mixing, or the lithium-containing composite oxide and the salt containing fluoride may be placed in a mortar and compressed and mixed with a pestle. The dry mixing may be performed, for example, at room temperature for 3 to 30 minutes.

[0037] [Negative electrode] The negative electrode 12 has, for example, a negative electrode core such as a metal foil and a negative electrode composite layer provided on the surface of the negative electrode core. The negative electrode core can be a foil of a metal such as copper that is stable within the potential range of the negative electrode, or a film with such a metal disposed on the surface layer. The negative electrode composite layer contains, for example, a negative electrode active material and a binder. The negative electrode can be produced, for example, by applying a negative electrode composite slurry containing the negative electrode active material, the binder, etc. to the negative electrode core, drying it to form a negative electrode composite layer, and then rolling this negative electrode composite layer.

[0038] The negative electrode mixture layer contains, as the negative electrode active material, for example, a carbon-based active material that reversibly absorbs and releases lithium ions. Suitable carbon-based active materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). The negative electrode active material may be a Si-based active material composed of at least one of Si and a Si-containing compound, or a combination of a carbon-based active material and a Si-based active material.

[0039] The binder contained in the negative electrode mixture layer can be, as in the case of the positive electrode, fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., but styrene-butadiene rubber (SBR) is preferred. The negative electrode mixture layer also preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, or PAA or a salt thereof.

[0040] [Separator] The separator is made of a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include polyolefins such as polyethylene and polypropylene, and cellulose. The separator may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator. [Example]

[0041] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0042] Example 1 [Synthesis of positive electrode active material] The median diameter (D50) is 17 μm and the composition is LiNi 0.8 Mn 0.2(NH4)2TiF6 was added at a ratio of 0.12 mol% to the lithium-containing composite oxide of O2, and the mixture was placed in a mortar and compressed and mixed with a pestle. This dry mixing was carried out at room temperature for 15 minutes. 0.8 Mn 0.2 A positive electrode active material was obtained in which (NH4)2TiOF4 was attached to the surface of the lithium-containing composite oxide represented by O2. It was confirmed by XRD that (NH4)2TiOF4 was attached to the surface of the lithium-containing composite oxide and that the amount was 0.12 mol%, the same as the added amount.

[0043] [Preparation of positive electrode] The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed in a solids mass ratio of 96.3:2.5:1.2, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added. The mixture was then kneaded to prepare a positive electrode composite slurry. The positive electrode composite slurry was applied to both sides of a positive electrode core made of aluminum foil, and the coating was dried. The coating was then rolled using a roller and cut to a predetermined electrode size, resulting in a positive electrode having a positive electrode composite layer formed on both sides of the positive electrode core.

[0044] [Preparation of non-aqueous electrolyte] A non-aqueous solvent was prepared by mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:6. LiPF6 was dissolved in the non-aqueous solvent at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0045] [Test cell construction] An electrode assembly was fabricated by attaching lead wires to the positive electrode and the counter electrode made of Li metal, and arranging the positive electrode and the counter electrode facing each other with a polyolefin separator in between. This electrode assembly and the non-aqueous electrolyte were enclosed in an exterior body made of an aluminum laminate film to fabricate a test cell.

[0046] [Evaluation of charge capacity, discharge capacity, and charge / discharge efficiency] In a temperature environment of 25°C, the cells were charged at a constant current of 0.2 C until the cell voltage reached 4.5 V, and then charged at a constant voltage of 0.02 C at 4.5 V. Subsequently, the cells were discharged at a constant current of 0.2 C until the cell voltage reached 2.5 V. The charge capacity and discharge capacity were measured. The discharge capacity was divided by the charge capacity to calculate the charge / discharge efficiency.

[0047] [Capacity retention rate evaluation] The test cell was charged at a constant current of 0.2 C in a temperature environment of 25°C until the battery voltage reached 4.5 V, and then charged at a constant voltage of 0.02 C at 4.5 V. It was then discharged at a constant current of 0.2 C until the battery voltage reached 2.5 V. This charge / discharge cycle was repeated 50 times. The discharge capacity at the first cycle and the discharge capacity at the 50th cycle were determined, and the capacity retention rate was calculated using the following formula. Capacity retention rate (%) = (50th cycle discharge capacity ÷ 1st cycle discharge capacity) × 100

[0048] <Example 2> A test cell was produced and evaluated in the same manner as in Example 1, except that the amount of (NH4)2TiF6 added in the synthesis of the positive electrode active material was changed to 0.25 mol %.

[0049] Example 3 In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was changed to 5 μm and the amount of (NH4)2TiF6 added was changed to 0.05 mol%.

[0050] Example 4 In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was changed to 5 μm and the amount of (NH4)2TiF6 added was changed to 0.25 mol%.

[0051] <Example 5> In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was changed to 5 μm and the amount of (NH4)2TiF6 added was changed to 0.34 mol%.

[0052] Example 6 In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was 5 μm and (NH4)2ZrF6 was added in place of (NH4)2TiF6 at a ratio of 0.12 mol% to the lithium-containing composite oxide.

[0053] Example 7 In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was 5 μm and (NH4)2ZrF6 was added in place of (NH4)2TiF6 at a ratio of 0.25 mol% to the lithium-containing composite oxide.

[0054] <Comparative Example 1> A test cell was produced and evaluated in the same manner as in Example 1, except that in the synthesis of the positive electrode active material, (NH4)2TiF6 was not added and the lithium-containing composite oxide was used as it was as the positive electrode active material.

[0055] <Comparative Example 2> In the synthesis of the positive electrode active material, a test cell was produced and evaluated in the same manner as in Example 1, except that the D50 of the lithium-containing composite oxide was 5 μm, (NH4)2TiF6 was not added, and the lithium-containing composite oxide was used as it was as the positive electrode active material.

[0056] <Comparative Example 3> A test cell was produced and evaluated in the same manner as in Example 1, except that in the synthesis of the positive electrode active material, Li2TiF6 was added in place of (NH4)2TiF6 at a ratio of 0.12 mol % to the lithium-containing composite oxide.

[0057] The results of the charge capacity, discharge capacity, charge / discharge efficiency, and capacity retention rate of the test cells of the examples and comparative examples are summarized in Table 1. Table 1 also shows the median diameter (D50) of the lithium-containing composite oxide, the composition and amount of additive, and the presence or absence of oxyfluoride on the surface of the lithium-containing composite oxide.

[0058] [Table 1]

[0059] All of the test cells of the Examples had higher capacity retention rates than the test cells of the Comparative Examples. Furthermore, the test cells of the Examples also exhibited performance comparable to that of the Comparative Examples in terms of charge capacity, discharge capacity, and charge / discharge efficiency. In Comparative Example 3, Li2TiF6 was present on the surface of the lithium-containing composite oxide without reacting with LiOH on the surface of the lithium-containing composite oxide. [Explanation of symbols]

[0060] 10 secondary battery, 11 positive electrode, 12 negative electrode, 12a winding end portion, 13 separator, 14 electrode body, 15 outer casing, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening, 27 gasket

Claims

1. The lithium-ion battery includes a core capable of reversibly absorbing and releasing lithium and a salt attached to a surface of the core, The active material for a non-aqueous electrolyte secondary battery, wherein the salt is (NH 4 ) 2 TiOF 4 or (NH 4 ) 2 ZrOF 4 .

2. The core has a layered structure and has the general formula Li ｘ Ni ｙ M2 １－ｙ O ２ 2. The active material for a non-aqueous electrolyte secondary battery according to claim 1, which is a lithium-containing composite oxide represented by the formula: (0.9≦x≦1.4, 0.4≦y≦1, M2 is at least one element selected from the group consisting of Mn, Co, Al, and Fe).

3. The active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein 0.7≦y≦1.

4. A non-aqueous electrolyte secondary battery comprising an electrode containing the active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, a counter electrode for said electrode, and an electrolyte.

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