JP2004220801A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery excellent both in discharge capacity and thermal stability. <P>SOLUTION: The nonaqueous electrolyte secondary battery is provided with a positive electrode containing a metal oxide with a composition expressed in a formula (1): Li<SB>2-x</SB>M<SB>1-y</SB>M'<SB>y</SB>X<SB>z</SB>AO<SB>4</SB>, a negative electrode and a nonaqueous electrolyte. In the formula, M expresses at least one kind of atoms selected from a group consisting of Ti, Nb, Mo and Ta, M' expresses at least one kind of atoms selected from a group consisting of V, Cr, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au, X expresses an atom of either O or F, A expresses at least a kind of atoms selected from a group of Si, Ge, P, and S, and x, y, and z satisfy the relationship: 0≤x≤2, 0≤y≤0.5, and 0.5≤z≤1.5, respectively. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００８２】
【表２】

【００８３】
表１〜２から明らかなように、前述した（１）式で表される組成を有する金属酸化物を正極活物質として用いる実施例１〜１８の二次電池は、いずれも破裂発火に到らずに安全に収束しており、かつ放電容量が比較例１〜５に比較して高いことがわかる。また、図４から、実施例１〜１８の二次電池は、放電時の電圧の平坦性が高いことが理解できる。さらに、表１，２の結果から、実施例１〜１８の中でも、実施例１、５、７、８、１０、１６，１８の二次電池は、平均放電電圧が高く、高いエネルギー密度を得られることがわかる。これは、金属酸化物に含まれる遷移金属元素のイオン半径（遷移金属元素の種類が２種類以上の場合には平均イオン半径）がより小さく、電気陰性度（遷移金属元素の種類が２種類以上の場合には平均電気陰性度）がより大きく、かつ価数（遷移金属元素の種類が２種類以上の場合には平均価数）が比較的大きいことが主な要因であると推測される。
【００８４】
これに対し、Ｌｉ_１．１Ｎｉ_０．７４Ｃｏ_０．１６Ｏ_１．８５Ｆ_０．１５で表される正極活物質を用いる比較例２には釘刺し試験と過充電試験において、また、ＬｉＣｏＯ_２を正極活物質として用いる比較例１には過充電試験において発火に到っている。一方、ＬｉＭｎ_２Ｏ_４を正極活物質として用いる比較例３の二次電池と、元素Ｍ´の原子比ｙが０．５を超えている正極活物質を用いる比較例４〜５の二次電池は、破裂・発火に到らないが、実施例１〜１８に比べ放電容量の点で劣っている。
【００８５】
【発明の効果】
以上詳述したように本発明によれば、放電容量が高く、かつ熱安定性に優れる非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る非水電解質二次電池に用いられる正極活物質の一例であるＭｏＯＰＯ_４の放電前のＸ線回折パターンを示す特性図。
【図２】図１の正極活物質の放電後のＸ線回折パターンを示す特性図。
【図３】本発明に係る非水電解質二次電池の一例である円筒形非水電解質二次電池を示す部分断面図。
【図４】実施例１の非水電解質二次電池における放電時の電池電圧変化を示す特性図。
【符号の説明】
１…容器、３…電極群、４…正極、５…セパレータ、６…負極、８…絶縁封口板、９…正極端子、１０…正極リード。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material containing a lithium-containing compound, and a nonaqueous electrolyte secondary battery provided with the positive electrode active material.
[0002]
[Prior art]
In recent years, non-aqueous electrolyte secondary batteries have attracted attention. This is probably because the successful development of a relatively safe anode material and the realization of a high-voltage battery by increasing the decomposition voltage of the non-aqueous electrolyte seem to be the major reasons. Among them, a secondary battery using lithium ions has a particularly high discharge potential, and thus is expected to realize a battery having a high energy density.
[0003]
As a positive electrode of a nonaqueous electrolyte secondary battery using lithium ions, a positive electrode including a transition element oxide called an active material, a binder, and a conductive agent for imparting conductivity to the active material is known. ing. The conductive agent is required to have a high conductivity and an oxidation resistance that is not oxidized by contact with the active material, and furthermore, a structure for making the active materials easily contact each other (for example, Fiber shape). Along with this requirement, in consideration of lightness and cost, a conductive agent such as carbon-based acetylene black has been used.
[0004]
On the other hand, as the positive electrode active material, LiCoO₂Such lithium cobalt oxides are often used. However, since the material cost is high and the energy density is low, development of a new positive electrode active material is demanded.
[0005]
By the way, Materials Research Bulletin, Vol. 33, no. 9, pp. 1339-1345, 1998, VOPO₄Hydrate, NbOPO₄Hydrate and MoOPO₄Is described as intercalating organic species such as pyridine, aniline or n-alkylamine without the reduction reaction of metal ions, but the application to non-aqueous electrolyte secondary batteries is described. There is no description.
[0006]
[Non-patent document 1]
Materials Research Bulletin, Vol. 33, no. 9, pp. 1339-1345, 1998
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a nonaqueous electrolyte secondary battery having both excellent discharge capacity and thermal stability.
[0008]
[Means for Solving the Problems]
A nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a metal oxide having a composition represented by the following formula (1), a negative electrode, and a nonaqueous electrolyte. .
[0009]
Li_{2- x}M_{1- y}M '_yX_zAO₄        (1)
Here, M is at least one element selected from the group consisting of Ti, Nb, Mo, Ta and W, and M ′ is V, Cr, Mn, Re, Fe, Co, Ni, Ru, Rh, X is at least one element selected from the group consisting of Pd, Os, Ir, Pt, Cu, Ag and Au, X is at least one of O and F, and A is Si, Ge, P And S are at least one element selected from the group consisting of: x, y, and z each represent 0 ≦ x ≦ 2, 0 ≦ y ≦ 0.5, and 0.5 ≦ z ≦ 1.5.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of the nonaqueous electrolyte secondary battery according to the present invention will be described.
[0011]
The nonaqueous electrolyte secondary battery includes a positive electrode containing a metal oxide having a composition represented by the following formula (1), a negative electrode, and a nonaqueous electrolyte.
[0012]
Li_{2- x}M_{1- y}M '_yX_zAO₄        (1)
Here, M is at least one element selected from the group consisting of Ti, Nb, Mo, Ta and W, and M ′ is V, Cr, Mn, Re, Fe, Co, Ni, Ru, Rh, X is at least one element selected from the group consisting of Pd, Os, Ir, Pt, Cu, Ag and Au, X is at least one of O and F, and A is Si, Ge, P And S are at least one element selected from the group consisting of: x, y, and z each represent 0 ≦ x ≦ 2, 0 ≦ y ≦ 0.5, and 0.5 ≦ z ≦ 1.5.
[0013]
According to such a secondary battery, both the discharge capacity and the thermal stability can be satisfied.
[0014]
That is, the above-mentioned metal oxide has PO in its crystal structure.₄Because of having a polyanion skeleton as described above, the crystal has high structural stability after charging. When this material is used as the positive electrode active material, the oxygen release / decomposition reaction after charging can be suppressed, so that combustion of the nonaqueous electrolyte when the battery temperature increases due to an internal short circuit or the like can be suppressed. Further, in the active material, as shown in the structural formula described above, two atoms of lithium can exist for one atom of the transition element M, and this lithium can participate in charge and discharge. Figure 1 (Positive electrode active material (MoOPO₄) Before discharge) and FIG. 2 (positive electrode active material after discharge (LiMoOPO)₄)), The crystal structure of the positive electrode active material belongs to the cubic system, and the change in the X-ray diffraction pattern before and after the discharge of the active material excludes the change in the lattice constant. Is not so noticeable. The valence of the transition element M contained in the active material is a so-called two-electron reaction system that can vary from trivalent to pentavalent. From these facts, according to the above-described metal oxide, a large discharge capacity can be obtained.
[0015]
Therefore, according to the present invention, a highly safe nonaqueous electrolyte secondary battery having a high capacity and a nonaqueous electrolyte combustion reaction during overcharge can be realized. In fact, as shown in Table 1 below, the secondary battery according to the present invention can suppress burst explosion in a nailing test after charging while securing a high discharge capacity, whereas the conventional secondary battery Has a low discharge capacity or ruptures or ignites.
[0016]
Hereinafter, the positive electrode, the negative electrode, and the non-aqueous electrolyte will be described.
[0017]
1) Positive electrode
First, the metal oxide represented by the above-described composition formula (1) will be described.
[0018]
A) Li
Lithium may or may not be contained in the metal oxide, but as it is contained, the amount of lithium involved in charge / discharge increases and the charge / discharge cycle life can be improved, preferable. When the atomic ratio x is 2, it is desirable to use a negative electrode containing lithium in advance, such as a lithium alloy or a lithium compound, as the negative electrode active material.
[0019]
B) Element M
Since the valence of the element M varies from trivalent to pentavalent, the above-described metal oxide can occlude and release two atoms of lithium ions in one molecule. Further, since the element M has a high bond strength with an oxygen atom, the oxygen release decomposition reaction of the active material can be suppressed. Among the elements M, Mo is particularly preferable.
[0020]
C) Element M '
The element M ′ is at least one element selected from the group consisting of V, Cr, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au. . Among them, Mn, Cr, and Fe are preferable.
[0021]
By including the element M 'in the metal oxide at an atomic ratio y of 0.5 or less, the voltage flatness in the charge / discharge curve or the charge / discharge cycle life of the secondary battery can be improved. However, if the atomic ratio y exceeds 0.5, sufficient electron conductivity cannot be obtained, which may cause deterioration of charge / discharge characteristics. A more preferred range is 0 ≦ y ≦ 0.2.
[0022]
D) Element X
The reason for limiting the atomic ratio z of the element X to the above range will be described. When the atomic ratio z is less than 0.5, the crystal structure is changed, and the number of Li accommodation sites is reduced, so that the capacity may be reduced. On the other hand, when the atomic ratio z exceeds 1.5, the distance between the transition elements is increased, which may cause a decrease in electron conductivity. A more preferred range is 0.8 ≦ z ≦ 1.2.
[0023]
E) Element A
As the element A, P is particularly preferable. This is because the stability of the crystal structure of the metal oxide is increased, so that the charge / discharge cycle life of the secondary battery can be improved.
[0024]
The metal oxide represented by the above formula (1) desirably has a tetragonal crystal structure, but may contain another crystal phase or an amorphous structure, or may have an amorphous structure.
[0025]
The metal oxide represented by the above formula (1) is produced, for example, by a solid phase method. Specifically, the powder of the compound of each constituent element is fired at about 250 ° C. in an atmosphere containing oxygen gas, and then fired at about 700 ° C. in a nitrogen atmosphere several times to obtain the above-described metal oxide. Can be obtained.
[0026]
As the positive electrode active material, only the metal oxide represented by the above-described formula (1) may be used, or a mixture of the metal oxide and another composite oxide may be used. Other composite oxides include LiCoO₂Lithium cobalt oxide such as LiNiCoO₂And a lithium-nickel-cobalt composite oxide as described above.
[0027]
The surface of the positive electrode active material may be coated with a lithium-containing conductive compound in order to improve the stability with respect to the nonaqueous electrolyte. The thickness of the lithium-containing conductive compound is preferably 0.3 nm or more. This is due to the following reasons. When the thickness is less than 0.3 nm, it becomes difficult to form a low-resistance film by mutual diffusion of the positive electrode active material and the lithium-containing conductive compound film. Further, a film thickness more preferably in the range of 10 nm or more as a range that can be manufactured more stably and has high mass productivity.
[0028]
For the positive electrode, for example, a positive electrode active material, a carbon-based conductive agent such as acetylene black, and a binder are suspended in an appropriate solvent, and the obtained suspension is applied to a current collector and dried. It is produced by press molding.
[0029]
As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like can be used.
[0030]
As the current collector, for example, an aluminum foil, a stainless steel foil, a titanium foil, or the like is preferably used.
[0031]
2) Negative electrode
As the negative electrode, for example, a material containing a substance that absorbs and releases lithium ions (for example, a carbonaceous material or a chalcogen compound), or a material made of a light metal can be used. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.
[0032]
Examples of the carbonaceous material that occludes and releases lithium ions include, for example, coke, carbon fiber, pyrolytic vapor-grown carbonaceous material, graphite, fired resin, mesophase pitch-based carbon fiber, and fired mesophase spherical carbon. it can. Among them, mesophase pitch-based carbon fibers graphitized at 2500 ° C. or higher or mesophase spherical carbon are preferable because the electrode capacity can be increased.
[0033]
The carbonaceous material particularly has an exothermic peak at 700 ° C. or higher in differential thermal analysis, more preferably an exothermic peak at 800 ° C. or higher, and a (101) diffraction peak (P) of a graphite structure by X-ray diffraction.₁₀₁) And (100) diffraction peaks (P₁₀₀) Intensity ratio P₁₀₁/ P₁₀₀Is preferably in the range of 0.7 to 2.2. Since the negative electrode containing such a carbonaceous material can rapidly store and release lithium ions, the rapid charge and discharge performance of the secondary battery is improved.
[0034]
Examples of the chalcogen compound that stores and releases lithium ions include titanium disulfide (TiS).₂), Molybdenum disulfide (MoS₂), Niobium selenide (NbSe)₂). When used for such a chalcogen compound negative electrode, the voltage of the secondary battery is reduced but the capacity of the negative electrode is increased, so that the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.
[0035]
Examples of the light metal include aluminum, an aluminum alloy, a magnesium alloy, a lithium metal, and a lithium alloy.
[0036]
A negative electrode containing a substance that absorbs and releases lithium ions is produced, for example, by suspending the substance and a binder in an appropriate solvent, applying the suspension to a current collector, drying, and then pressing. Is done.
[0037]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Can be used.
[0038]
As the current collector, for example, a copper foil, a stainless steel foil, a nickel foil, or the like is preferably used.
[0039]
Further, the transition element M of the metal oxide represented by the formula (1) used as the positive electrode active material in the present invention is, for example, Zr, Nb, Ta, Hf, or the like, so that the material has a lower potential than the positive electrode. It is also possible to use it as an active material, and it is also possible to use B, Al, Sn, As, S, Se, and Te as the element A.
[0040]
3) Non-aqueous electrolyte
Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte (non-aqueous electrolyte) prepared by dissolving an electrolyte in a non-aqueous solvent, and a polymer gel in which a polymer material holds a non-aqueous solvent and an electrolyte. A non-aqueous electrolyte, a solid non-aqueous electrolyte obtained by holding an electrolyte in a polymer material, and the like.
[0041]
Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC); Chain ethers such as dimethoxyethane (DME), diethoxyethane (DEE) and ethoxymethoxyethane, cyclic ethers and crown ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), and γ-butyrolactone (γ- Fatty acid esters such as BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO). The non-aqueous solvents may be used alone or as a mixture of two or more.
[0042]
Above all, at least one selected from EC, PC, and γ-BL, and at least one selected from EC, PC, and γ-BL and DMC, EMC, DEC, DME, DEE, THF, 2-MeTHF, and AN It is desirable to use a mixed solvent composed of at least one selected. Further, when a negative electrode containing a carbonaceous material that occludes and releases lithium ions is used, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, and EC and PC And EMC, EC and PC and DEC, EC and PC and DEE, EC and AN, EC and EMC, PC and DMC, PC and DEC, and EC and DEC.
[0043]
As the electrolyte, for example, lithium perchlorate (LiClO₄), Lithium hexafluorophosphate (LiPF)₆), Lithium tetrafluoroborate (LiBF₄), Lithium arsenic hexafluoride (LiAsF)₆), Lithium trifluorometasulfonate (LiCF₃SO₃), Lithium bistrifluoromethylsulfonylimide (LiN (CF₃SO₂)₂)). Among them, LiPF₆, LiBF₄, LiN (CF₃SO₂)₂The use of is preferred because conductivity and safety are improved.
[0044]
The amount of the electrolyte dissolved in the nonaqueous solvent is preferably in the range of 0.1 mol / L to 3 mol / L.
[0045]
Examples of the polymer material contained in the gel non-aqueous electrolyte and the solid non-aqueous electrolyte include polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or acrylonitrile, acrylate, vinylidene fluoride Alternatively, a polymer containing ethylene oxide as a monomer can be used.
[0046]
A cylindrical non-aqueous electrolyte secondary battery as an example of the non-aqueous electrolyte battery according to the present invention will be described with reference to FIG.
[0047]
For example, a cylindrical container 1 having a bottom made of stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3 is produced by, for example, spirally winding a separator 5 between the positive electrode 4 and the negative electrode 6. The separator 5 is formed of, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, or a polypropylene porous film.
[0048]
The non-aqueous electrolyte is contained in the container 1. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is disposed in the upper opening of the container 1 and the vicinity of the upper opening is caulked inward to fix the sealing plate 8 to the container 1 in a liquid-tight manner. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6 is connected to the container 1 serving as a negative terminal via a negative lead (not shown).
[0049]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and can be implemented by appropriately changing the scope of the invention without changing the gist of the invention.
[0050]
(Example 1)
<Preparation of positive electrode>
Lithium-containing molybdenum phosphate oxide (Li₂MoOPO₄) Was synthesized as follows.
[0051]
As a starting material, molybdenum dioxide (MoO₂) And ammonium dihydrogen phosphate (NH₄H₂PO₄) Was carefully ground and mixed at a molar ratio of 1: 1 and then fired at 250 ° C. in the air for 10 hours. Next, after pulverizing again, it was baked at 700 ° C. for 10 hours in a nitrogen gas flow. While watching the X-ray diffraction pattern, molybdenum oxide phosphate (MoOPO)₄The firing at 700 ° C. was repeated several times until a single phase was obtained. The resulting molybdenum oxide phosphate (MoOPO)₄) And lithium carbonate (Li₂CO₃) Were mixed at a molar ratio of 1: 1 and calcined at 900 ° C. for 10 hours in a nitrogen gas containing 5% of hydrogen to obtain lithium-containing molybdenum oxide (Li₂MoOPO₄) Got. As a result of X-ray diffraction, it was found that the obtained oxide had a tetragonal crystal structure.
[0052]
The powder was appropriately measured with a particle size distribution meter, and pulverized until a target particle size distribution was obtained. This powder was used as a positive electrode active material, and 2.5% by weight of a positive electrode active material powder, 2.5% by weight of acetylene black powder and graphite powder as conductive agents, and 3% by weight of PVDF powder as a binder. Were mixed and dispersed in an N-methyl-2-pyrrolidone solvent to prepare a positive electrode mixture slurry. This slurry was applied on an aluminum foil, dried, and then rolled and cut to give a basis weight of 100 g / m2.²Of 10C-class high-output battery specifications.
[0053]
<Preparation of negative electrode>
80% by weight of mesophase pitch carbon fiber as a negative electrode active material, 20% by weight of graphite powder as a conductive agent, 1.2% by weight of carboxymethyl cellulose as a binder, and 1.76% by weight of styrene butadiene rubber And water were added and dispersed carefully to prepare a negative electrode mixture slurry. The obtained slurry was coated on copper foil, dried, rolled and cut, and the basis weight was 72 g / m2.²Was produced.
[0054]
<Preparation of non-aqueous electrolyte>
LiPF as electrolyte in mixed solvent consisting of propylene carbonate and dimethoxyethane₆Was dissolved to a concentration of 1 mol / L to prepare a non-aqueous electrolyte.
[0055]
<Preparation of battery for evaluation>
After the obtained positive electrode, negative electrode sheet and separator were sufficiently dried, an electrode group was produced by spirally winding the separator with the separator interposed between the positive electrode and the negative electrode. This electrode group was inserted between stainless steel members, and an electrolyte was injected and sealed in an argon atmosphere, thereby producing an evaluation battery having the structure shown in FIG. 1 described above. At this time, the length of the electrode was set so as to fit in a 18650 type battery can.
[0056]
(Example 2)
Lithium-containing niobium oxide sulfate (Li₂NbOPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0057]
(Example 3)
Lithium-containing tantalum phosphorus oxide (Li₂TaOPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0058]
(Example 4)
Lithium-containing tungsten oxysulfuric acid (Li₂WOPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0059]
(Example 5)
Lithium-containing molybdenum iron phosphate oxide (Li₂Mo_0.67Fe_0.33OPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0060]
(Example 6)
Lithium-containing tungsten oxide silicate (Li₂WOSiO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0061]
(Example 7)
As the positive electrode active material, lithium-containing molybdenum germanium oxide (Li₂MoOGeO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0062]
(Example 8)
Lithium-containing molybdenum ruthenium phosphate oxide (Li₂Mo_0.9Ru_0.1OPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0063]
(Example 9)
Lithium-containing tantalum iron phosphate fluoride (Li₂Ta_0.5Fe_0.5FPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0064]
(Example 10)
Lithium-containing molybdenum titanium phosphate oxide (Li₂Mo_0.5Ti_0.5OPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0065]
(Example 11)
As a positive electrode active material, lithium-containing molybdenum rhodium phosphate oxide (Li₂Mo_0.9Rh_0.1OPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0066]
(Example 12)
Lithium-containing molybdenum niobium phosphate oxide (Li₂Mo_0.5Nb_0.5OPO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0067]
(Example 13)
Lithium-containing titanium oxide sulfate (Li₂TiOSO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0068]
(Example 14)
Lithium-containing titanium vanadium oxysulfide (Li₂Ti_0.5V_0.5OSO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0069]
(Example 15)
Lithium-containing vanadium niobium sulfate (Li₂V_0.5Nb_0.5OSO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0070]
(Example 16)
Lithium-containing molybdenum phosphate oxide (Li₂MoO_1.5PO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0071]
(Example 17)
As a positive electrode active material, lithium-containing titanium oxide (Li)₂TiO_0.5PO₄1) The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the powder was used.
[0072]
(Example 18)
Molybdenum phosphorous oxide (MoO)_1.5PO₄) Powder and lithium cobalt nitride (Li_2.6Co_0.4A positive electrode evaluation battery shown in FIG. 1 described above was assembled in the same configuration as in Example 1 except that N) was used.
[0073]
(Comparative Example 1)
LiCoO as positive electrode active material₂Using a powder and a basis weight of the negative electrode of 40 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except for the above.
[0074]
(Comparative Example 2)
Li as the positive electrode active material_1.1Ni_0.74Co_0.16O_1.85F_0.15Using a powder and a basis weight of the negative electrode of 60 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except for the above.
[0075]
(Comparative Example 3)
LiMn as positive electrode active material₂O₄Using a powder and a basis weight of the negative electrode of 35 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except for the above.
[0076]
(Comparative Examples 4 and 5)
A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except that a metal oxide having a composition shown in Table 2 below was used as a positive electrode active material.
[0077]
With respect to the obtained batteries of Examples 1 to 18 and Comparative Examples 1 to 5, the thermal stability and the discharge capacity during charging were measured by the method described below, and the results are shown in Tables 1 and 2 below.
[0078]
(Measurement of exothermic peak in nail penetration test)
After charging each secondary battery at a current value of 0.3 C until it reached 4.2 V, current was continuously supplied so as to maintain the voltage, and the current was stopped when the total charging time reached 5 hours. Then, a thermocouple was attached to the battery that had been subjected to the above-mentioned charging treatment, a nail having a diameter of 2 mm was pierced from the side of the battery at a speed of 13.5 cm / sec, and the time change of the battery temperature was measured. Was measured.
[0079]
(Overcharge test)
For each secondary battery, an overcharge test in which charging was continued to 15 V with a current of 6 C was performed, and the presence or absence of rupture and ignition was examined.
[0080]
(Measurement of discharge capacity)
For each secondary battery, a constant current / constant voltage charge was performed at a current value of 0.3 C up to 4.2 V, and then a discharge capacity at the time of discharging to 2.7 V at a current value of 0.3 C was measured. The obtained discharge capacity and the average discharge voltage obtained from the voltage curve at the time of discharge are also shown in Tables 1 and 2 below. FIG. 4 shows the result of the secondary battery of Example 1 among the voltage change curves at the time of discharging.
[0081]
[Table 1]

[0082]
[Table 2]

[0083]
As is clear from Tables 1 and 2, all of the secondary batteries of Examples 1 to 18 using the metal oxide having the composition represented by the above formula (1) as the positive electrode active material lead to burst ignition. It can be seen that the convergence is safe and the discharge capacity is higher than those of Comparative Examples 1 to 5. FIG. 4 shows that the secondary batteries of Examples 1 to 18 have high voltage flatness during discharge. Furthermore, from the results of Tables 1 and 2, among the Examples 1 to 18, the secondary batteries of Examples 1, 5, 7, 8, 10, 16, and 18 have a high average discharge voltage and a high energy density. It is understood that it can be done. This is because the ionic radius of the transition metal element contained in the metal oxide (the average ionic radius when there are two or more types of transition metal elements) is smaller, and the electronegativity (the type of the transition metal element is two or more types). In this case, it is estimated that the main factors are that the average electronegativity is larger and the valence (the average valence when there are two or more kinds of transition metal elements) is relatively large.
[0084]
On the other hand, Li_1.1Ni_0.74Co_0.16O_1.85F_0.15Comparative Example 2 using a positive electrode active material represented by₂In Comparative Example 1 in which is used as the positive electrode active material, ignition has occurred in the overcharge test. On the other hand, LiMn₂O₄The secondary batteries of Comparative Example 3 using as the positive electrode active material and the secondary batteries of Comparative Examples 4 and 5 using the positive electrode active material in which the atomic ratio y of the element M ′ exceeds 0.5 are ruptured and ignited. Although it does not reach, it is inferior in discharge capacity as compared with Examples 1-18.
[0085]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having a high discharge capacity and excellent thermal stability.
[Brief description of the drawings]
FIG. 1 shows MoOPO which is an example of a positive electrode active material used in a non-aqueous electrolyte secondary battery according to the present invention.₄FIG. 4 is a characteristic diagram showing an X-ray diffraction pattern before discharge.
FIG. 2 is a characteristic diagram showing an X-ray diffraction pattern of the positive electrode active material of FIG. 1 after discharging.
FIG. 3 is a partial sectional view showing a cylindrical non-aqueous electrolyte secondary battery as an example of the non-aqueous electrolyte secondary battery according to the present invention.
FIG. 4 is a characteristic diagram showing a battery voltage change at the time of discharging in the non-aqueous electrolyte secondary battery of Example 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... container, 3 ... electrode group, 4 ... positive electrode, 5 ... separator, 6 ... negative electrode, 8 ... insulating sealing plate, 9 ... positive electrode terminal, 10 ... positive electrode lead.

Claims (2)

A nonaqueous electrolyte secondary battery comprising: a positive electrode containing a metal oxide having a composition represented by the following formula (1); a negative electrode; and a nonaqueous electrolyte.
_{Li 2- x M 1- y M'y} X z AO 4 (1)
Here, M is at least one element selected from the group consisting of Ti, Nb, Mo, Ta and W, and M ′ is V, Cr, Mn, Re, Fe, Co, Ni, Ru, Rh, X is at least one element selected from the group consisting of Pd, Os, Ir, Pt, Cu, Ag and Au, X is at least one of O and F, and A is Si, Ge, P And S are at least one element selected from the group consisting of x, y and z, respectively, where 0 ≦ x ≦ 2, 0 ≦ y ≦ 0.5, and 0.5 ≦ z ≦ 1.5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal oxide has a tetragonal crystal structure.

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