JP3887317B2 - Nonaqueous electrolyte secondary battery - Google Patents

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１〜１２及び１５，１６，１８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１〜１２及び１５，１６，１８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１〜１２及び１５，１６，１８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、ＬｉＣｏＯ₂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、ＬｉＭｎ₂Ｏ₄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１〜１２及び１５，１６，１８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ＭｏＯＰＯ₄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]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material containing a lithium-containing compound and a nonaqueous electrolyte secondary battery including the positive electrode active material.
[0002]
[Prior art]
In recent years, non-aqueous electrolyte secondary batteries have attracted attention. This is probably due to the successful development of a relatively safe negative electrode material and the realization of a high-voltage battery by increasing the decomposition voltage of the nonaqueous electrolyte. Among these, secondary batteries using lithium ions are expected to realize a battery having a high energy density because the discharge potential is particularly high.
[0003]
As a positive electrode of a non-aqueous electrolyte secondary battery using lithium ions, one containing a transition element oxide called an active material, a binder, and a conductive agent for imparting conductivity to the active material is known. ing. In addition to high conductivity, this conductive agent is required to have oxidation resistance that does not oxidize even when contacted with the active material. Further, a structure for easily bringing the active materials into electrical contact (for example, Fiber shape). In combination with this requirement, a conductive agent such as carbon-based acetylene black has been conventionally used in consideration of light weight and cost.
[0004]
On the other hand, the positive electrode active material has conventionally been LiCoO.₂Lithium cobalt oxide is often used, but since the material cost is high and the energy density is low, the development of a novel positive electrode active material is desired.
[0005]
By the way, Materials Research Bulletin, Vol.33, No.9, pp.1339-1345, 1998 includes VOPO._FourHydrate of NbOPO_FourHydrates and MoOPO_FourIs described as intercalating organic species such as pyridine, aniline or n-alkylamine without a reduction reaction of metal ions, but for application to non-aqueous electrolyte secondary batteries. 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 this invention is to provide the nonaqueous electrolyte secondary battery which is excellent in both discharge capacity and thermal stability.
[0008]
[Means for Solving the Problems]
  The nonaqueous electrolyte secondary battery according to the present invention has a composition represented by the following formula (1):And the tetragonal crystal structureAnd a negative electrode and a non-aqueous electrolyte.
[0009]
      Li_{2- x}M_{1- y}M '_yX_zAO_Four        (1)
  However, M is at least one element selected from the group consisting of Ti, Nb, Mo, Ta and W (except when M is Ti alone), and M ′ isV, Fe, Ru and RhAt least one element selected from the group consisting of: X is at least one element selected from O and F; A is at least one element selected from the group consisting of Si, Ge, P and S; X, y, and z represent 0 ≦ x ≦ 2, 0 ≦ y ≦ 0.5, and 0.5 ≦ z ≦ 1.5, respectively.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of the nonaqueous electrolyte secondary battery according to the present invention will be described.
[0011]
This nonaqueous electrolyte secondary battery includes a positive electrode including 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_zAO_Four        (1)
Where 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, It is at least one element selected from the group consisting of Pd, Os, Ir, Pt, Cu, Ag and Au, X is composed of at least one element of O and F, and A is Si, Ge, P And S, at least one element selected from the group consisting of S and x, y, and z respectively 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 aforementioned metal oxide has PO in its crystal structure._FourTherefore, the structure stability of the crystal after charging is high. When this material is used as the positive electrode active material, the oxygen release decomposition reaction after charging can be suppressed, so that the nonaqueous electrolyte can be prevented from burning when the battery temperature rises due to an internal short circuit or the like. In addition, as shown in the structural formula described above, this active material can contain two lithium atoms per one transition element M, and this lithium can be involved in charge and discharge. Fig. 1 (Positive electrode active material (MoOPO_FourX-ray diffraction pattern before discharge) and FIG. 2 (positive electrode active material after discharge (LiMoOPO)_FourAs is clear from the X-ray diffraction pattern), the crystal structure of the positive electrode active material belongs to the cubic system, and the change of the X-ray diffraction pattern before and after the discharge of the active material excludes the change of the lattice constant. It can be understood that it is not so remarkable. In addition, 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 things, according to the metal oxide mentioned above, a big discharge capacity can be obtained.
[0015]
Therefore, according to the present invention, it is possible to realize a non-aqueous electrolyte secondary battery having a high capacity and a highly safe non-aqueous electrolyte combustion reaction at the time of overcharging. Actually, as shown in Table 1 to be described later, the secondary battery according to the present invention can suppress burst ignition in the nail test after charging while securing a high discharge capacity, whereas the conventional secondary battery. May have a low discharge capacity or may rupture or ignite.
[0016]
Hereinafter, the positive electrode, the negative electrode, and the nonaqueous electrolyte will be described.
[0017]
1) Positive electrode
First, the metal oxide represented by the composition formula (1) described above will be described.
[0018]
A) Li
Lithium may or may not be contained in the metal oxide, but if 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 metal oxide described above can occlude and release diatomic lithium ions per molecule. Further, since the element M has a high bond strength with oxygen atoms, 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. . Of these, 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 preferable range is 0 ≦ y ≦ 0.2.
[0022]
D) Element X
The reason why the atomic ratio z of the element X is limited to the above range will be described. If the atomic ratio z is less than 0.5, the crystal structure may be changed, causing a decrease in the capacity of the Li containing site and possibly reducing the capacity. 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 preferable range is 0.8 ≦ z ≦ 1.2.
[0023]
E) Element A
Among them, P is preferable as the element A. 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 include other crystal phases or amorphous structures, or may have an amorphous structure.
[0025]
The metal oxide represented by the above formula (1) is produced by, for example, 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 repeat the above-described metal oxide. Can be obtained.
[0026]
Only the metal oxide represented by the above-described formula (1) may be used for the positive electrode active material, or a mixture of the metal oxide and another composite oxide may be used. Other composite oxides include LiCoO₂Lithium cobalt oxide such as LiNiCoO₂Lithium nickel cobalt composite oxide and the like can be used.
[0027]
The surface of the positive electrode active material may be coated with a lithium-containing conductive compound in order to improve stability with respect to the nonaqueous electrolyte. The film thickness of the lithium-containing conductive compound is preferably 0.3 nm or more. This is due to the following reason. If the film 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 more preferable film thickness is in the range of 10 nm or more as a range that can be more stably produced and is rich in mass productivity.
[0028]
For example, the positive electrode is obtained by suspending a positive electrode active material, a carbon-based conductive agent such as acetylene black, and a binder in an appropriate solvent, and applying the obtained suspension to a current collector and drying it. It is produced by press molding.
[0029]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR).
[0030]
As the current collector, for example, aluminum foil, stainless steel foil, titanium foil or the like is preferably used.
[0031]
2) Negative electrode
As this negative electrode, for example, a material containing a substance that occludes / releases lithium ions (for example, a carbonaceous material or a chalcogen compound) or a material made of a light metal can be used. Among them, a negative electrode containing a carbonaceous material or a chalcogen compound that occludes / 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 / releases lithium ions include coke, carbon fiber, pyrolytic vapor-grown carbonaceous material, graphite, resin fired body, mesophase pitch carbon fiber, and mesophase spherical carbon fired body. it can. Among these, mesophase pitch carbon fibers graphitized at 2500 ° C. or higher or mesophase spherical carbon is preferable because the electrode capacity can be increased.
[0033]
The carbonaceous material particularly has an exothermic peak at 700 ° C. or higher, more preferably 800 ° C. or higher by differential thermal analysis, and has a (101) diffraction peak (P₁₀₁) And (100) diffraction peak (P₁₀₀) Strength ratio P₁₀₁/ P₁₀₀Is preferably in the range of 0.7 to 2.2. Since the negative electrode including such a carbonaceous material can rapidly occlude / release lithium ions, the rapid charge / discharge performance of the secondary battery is improved.
[0034]
Examples of the chalcogen compound that absorbs and releases lithium ions include titanium disulfide (TiS).₂), Molybdenum disulfide (MoS)₂), Niobium selenide (NbSe)₂) And the like. When used for such a chalcogen compound negative electrode, although the voltage of the secondary battery decreases, the capacity of the negative electrode increases, so that the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the quick charge / discharge performance of the secondary battery is improved.
[0035]
Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, and lithium alloy.
[0036]
A negative electrode containing a substance that occludes / releases lithium ions is prepared, 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 above formula (1) used as the positive electrode active material in the present invention is changed to, for example, Zr, Nb, Ta, Hf or the like to make a material having 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, 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 non-aqueous solvent and an electrolyte are held in a polymer material. And a solid nonaqueous electrolyte in which an electrolyte is held in a polymer material.
[0041]
Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), for example, chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Chain ethers such as dimethoxyethane (DME), diethoxyethane (DEE), ethoxymethoxyethane, cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), crown ethers, γ-butyrolactone (γ- BL) and the like, nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO). The non-aqueous solvent may be used alone or in combination of two or more.
[0042]
Among these, 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. Moreover, when using what contains the carbonaceous material which occludes and discharge | releases the said lithium ion for a negative electrode, from a viewpoint of improving the cycle life of the secondary battery provided with the said negative electrode, EC and PC, (gamma) -BL, EC and PC It is desirable to use a mixed solvent consisting of EC 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]
Examples of the electrolyte include lithium perchlorate (LiClO).₄), Lithium hexafluorophosphate (LiPF)₆), Lithium tetrafluoroborate (LiBF)₄), Lithium hexafluoroarsenide (LiAsF)₆), Lithium trifluorometasulfonate (LiCF)₃SO₃), Bistrifluoromethylsulfonylimide lithium (LiN (CF₃SO₂)₂) And the like. Among them, LiPF₆, LiBF₄, LiN (CF₃SO₂)₂Is preferable because conductivity and safety are improved.
[0044]
The amount of the electrolyte dissolved in the non-aqueous 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-like nonaqueous electrolyte and the solid nonaqueous electrolyte include polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), acrylonitrile, acrylate, and vinylidene fluoride. Or the polymer etc. which contain ethylene oxide as a monomer can be mentioned.
[0046]
A cylindrical nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte battery according to the present invention will be described with reference to FIG.
[0047]
For example, a bottomed cylindrical container 1 made of stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is accommodated in the container 1. The electrode group 3 is produced, for example, by winding the separator 5 between the positive electrode 4 and the negative electrode 6 in a spiral shape. The separator 5 is made of, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, or a polypropylene porous film.
[0048]
The nonaqueous electrolyte is accommodated in the container 1. The insulating paper 7 having a central opening 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 sealing plate 8 is liquid-tightly fixed to the container 1 by caulking the vicinity of the upper opening inward. The positive 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 which is a negative electrode terminal via a negative electrode lead (not shown).
[0049]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following Example at all, In the range which does not change the summary, it can change suitably and can implement.
[0050]
Example 1
<Preparation of positive electrode>
Lithium-containing molybdenum-phosphorus oxide (Li₂MoOPO_Four) Was synthesized as follows.
[0051]
Molybdenum dioxide (MoO) as a starting material₂) And ammonium dihydrogen phosphate (NH_FourH₂PO_Four) Was carefully pulverized and mixed at a molar ratio of 1: 1, and then fired at 250 ° C. for 10 hours in the atmosphere. Then, after pulverizing again, it was fired at 700 ° C. for 10 hours in a nitrogen gas flow. While looking at the X-ray diffraction pattern, molybdenum oxide phosphate (MoOPO_FourThe firing at 700 ° C. was repeated several times until a single phase was obtained. The resulting molybdenum oxide phosphate (MoOPO_Four) And lithium carbonate (Li₂CO_ThreeAre 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 a lithium-containing molybdenum oxide phosphorous oxide (Li₂MoOPO_Four) As a result of X-ray diffraction, the obtained oxide was found to have a tetragonal crystal structure.
[0052]
This powder was appropriately measured with a particle size distribution meter and pulverized until the desired particle size distribution was obtained. This powder was used as a positive electrode active material, the positive electrode active material powder was 2.5% by weight, acetylene black powder and graphite powder as conductive agents were 2.5% by weight, and PVDF powder as a binder was 3% by weight. Were mixed and dispersed in an N-methyl-2-pyrrolidone solvent to prepare a positive electrode mixture slurry. The slurry is coated on an aluminum foil, dried, and then rolled and cut to give a basis weight of 100 g / m.²The positive electrode of 10C class high output battery specification was obtained.
[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 carboxymethylcellulose as a binder, and 1.76% by weight of styrene butadiene rubber Were mixed and water was added and dispersed carefully to prepare a negative electrode mixture slurry. The obtained slurry was coated on a copper foil, dried, rolled and cut, and the basis weight was 72 g / m.²A negative electrode was prepared.
[0054]
<Preparation of non-aqueous electrolyte>
LiPF as electrolyte in mixed solvent consisting of propylene carbonate and dimethoxyethane₆Was dissolved so as to have a concentration of 1 mol / L to prepare a non-aqueous electrolyte.
[0055]
<Production of evaluation battery>
After the obtained positive electrode, negative electrode sheet and separator were sufficiently dried, the separator was interposed between the positive electrode and the negative electrode and wound in a spiral shape to produce an electrode group. By inserting this electrode group between stainless steel and injecting an electrolyte solution in an argon atmosphere and sealing it, a battery for evaluation having the structure shown in FIG. 1 was prepared. At this time, the length of the electrode was set so that it would just fit in a 18650 type battery can.
[0056]
(Example 2)
Lithium-containing niobium oxide sulfate (Li₂NbOPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0057]
(Example 3)
Lithium-containing tantalum phosphorus oxide (Li₂TaOPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0058]
(Example 4)
Lithium-containing tungsten oxide sulfate (Li₂WOPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0059]
(Example 5)
Lithium-containing molybdenum iron phosphate oxide (Li₂Mo_0.67Fe_0.33OPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0060]
(Example 6)
Lithium-containing tungsten oxide silicate (Li₂WOSiO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0061]
(Example 7)
Lithium-containing molybdenum oxide germanium oxide (Li₂MoOGeO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0062]
(Example 8)
Lithium-containing molybdenum ruthenium phosphate oxide (Li₂Mo_0.9Ru_0.1OPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0063]
Example 9
Lithium-containing tantalum iron fluoride phosphate (Li₂Ta_0.5Fe_0.5FPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0064]
(Example 10)
Lithium-containing molybdenum titanium phosphorous oxide (Li₂Mo_0.5Ti_0.5OPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0065]
(Example 11)
Lithium-containing molybdenum rhodium oxide phosphorous oxide (Li₂Mo_0.9Rh_0.1OPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0066]
(Example 12)
Lithium-containing molybdenum niobium phosphorous oxide (Li₂Mo_0.5Nb_0.5OPO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0067]
  (referenceExample 13)
  Lithium-containing titanium oxide sulfate (Li₂TiOSO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0068]
  (referenceExample 14)
  Lithium-containing titanium vanadium oxide (Li) as the positive electrode active material₂Ti_0.5V_0.5OSO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0069]
(Example 15)
Lithium-containing vanadium niobium oxide sulfate (Li₂V_0.5Nb_0.5OSO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0070]
(Example 16)
Lithium-containing molybdenum oxide phosphorous oxide (Li₂MoO_1.5PO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0071]
  (referenceExample 17)
  Lithium-containing titanium phosphorous oxide (Li₂TiO_0.5PO₄1) The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that powder was used.
[0072]
(Example 18)
Molybdenum phosphorus oxide (MoO) as the positive electrode active material_1.5PO₄) Powder and lithium cobalt nitride (Li_2.6Co_0.4The positive electrode evaluation battery shown in FIG. 1 was assembled in the same configuration as in Example 1 except that N) was used.
[0073]
(Comparative Example 1)
LiCoO as positive electrode active material₂Powder is used and the basis weight of the negative electrode is 40 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except that.
[0074]
(Comparative Example 2)
Li as the positive electrode active material_1.1Ni_0.74Co_0.16O_1.85F_0.15Powder is used and the basis weight of the negative electrode is 60 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except that.
[0075]
(Comparative Example 3)
LiMn as positive electrode active material₂O₄Powder is used and the basis weight of the negative electrode is 35 g / m²A positive electrode evaluation battery having the same configuration as that described in Example 1 was assembled except that.
[0076]
(Comparative Examples 4-5)
A positive electrode evaluation battery having the same structure as described in Example 1 was assembled except that a metal oxide having the composition shown in Table 2 below was used as the positive electrode active material.
[0077]
  Examples 1 to 1 obtained12, 15, 16,18Reference Examples 13, 14, and 17And about the battery of Comparative Examples 1-5, the thermal stability at the time of charge and discharge capacity were measured by the method demonstrated below, and the result is shown to the following Tables 1-2.
[0078]
(Measurement of exothermic peak in nail penetration test)
About each secondary battery, it charged until it reached 4.2V with the electric current value of 0.3C, Then, the electric current was continuously sent so that voltage might be maintained, and the electric current was stopped when the total charging time became 5 hours. After that, a thermocouple was attached to the battery that had been subjected to the above-mentioned charging treatment, a nail with a diameter of 2 mm was inserted from the side of the battery at a speed of 13.5 cm / sec, the time change of the temperature of the battery was measured, and the exothermic peak temperature Was measured.
[0079]
(Overcharge test)
Each secondary battery was subjected to an overcharge test in which the battery was continuously charged to 15 V at a current of 6 C, and the presence or absence of rupture and ignition was examined.
[0080]
(Measurement of discharge capacity)
About each secondary battery, after performing the constant current constant voltage charge to 4.2V with the current value of 0.3C, the discharge capacity at the time of discharging to 2.7V with the current value of 0.3C was measured. The obtained discharge capacity and the average discharge voltage obtained from the voltage curve during discharge are shown in Tables 1 and 2 below. Moreover, the result about the secondary battery of Example 1 among the voltage change curves at the time of this discharge is shown in FIG.
[0081]
[Table 1]

[0082]
[Table 2]

[0083]
  As is clear from Tables 1 and 2, Examples 1 to 1 using the metal oxide having the composition represented by the above formula (1) as the positive electrode active material12, 15, 16,It can be seen that all of the 18 secondary batteries converged safely without reaching bursting ignition, and the discharge capacity was higher than those of Comparative Examples 1-5. Also, from FIG.12, 15, 16,It can be understood that No. 18 secondary battery has high voltage flatness during discharge. Furthermore, from the results of Tables 1 and 2, Examples 1 to12, 15, 16,18 shows that the secondary batteries of Examples 1, 5, 7, 8, 10, 16, and 18 have a high average discharge voltage and a high energy density. 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 transition metal elements) is smaller, and the electronegativity (two or more types of transition metal elements). In this case, it is presumed that the main factors are that the average electronegativity) is larger and the valence (the average valence when the number of transition metal elements is two or more) is relatively large.
[0084]
  In contrast, Li_1.1Ni_0.74Co_0.16O_1.85F_0.15In Comparative Example 2 using the positive electrode active material represented by the following formula, in the nail penetration test and the overcharge test, LiCoO₂In Comparative Example 1 in which is used as the positive electrode active material, ignition occurred in the overcharge test. Meanwhile, LiMn₂O_FourThe secondary battery of Comparative Example 3 using As a positive electrode active material and the secondary batteries of Comparative Examples 4 to 5 using a positive electrode active material in which the atomic ratio y of the element M ′ exceeds 0.5 are used for rupture and ignition. Although not reached, Examples 1 to12, 15, 16,Compared to 18, it is inferior in terms of discharge capacity.
[0085]
【The invention's effect】
As described above in detail, according to the present invention, a nonaqueous electrolyte secondary battery having a high discharge capacity and excellent thermal stability can be provided.
[Brief description of the drawings]
FIG. 1 shows MoOPO as an example of a positive electrode active material used in a nonaqueous electrolyte secondary battery according to the present invention._FourThe characteristic view which shows the X-ray-diffraction pattern before electrical discharge.
FIG. 2 is a characteristic diagram showing an X-ray diffraction pattern after discharge of the positive electrode active material of FIG.
FIG. 3 is a partial cross-sectional view showing a cylindrical nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention.
4 is a characteristic diagram showing a change in battery voltage during discharge in the nonaqueous electrolyte secondary battery of Example 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Container, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 8 ... Insulation sealing board, 9 ... Positive electrode terminal, 10 ... Positive electrode lead.

Claims (2)

A nonaqueous electrolyte secondary battery comprising a positive electrode including a metal oxide having a composition represented by the following formula (1) and a tetragonal crystal structure , a negative electrode, and a nonaqueous electrolyte.
_{Li 2- x M 1- y M'y} X z AO 4 (1)
M is at least one element selected from the group consisting of Ti, Nb, Mo, Ta, and W (except when M is Ti alone), and M ′ is V, Fe, Ru. And at least one element selected from the group consisting of Rh , X is at least one element selected from O and F, and A is at least one selected from the group consisting of Si, Ge, P and S. X, y, and z are 0 ≦ x ≦ 2, 0 ≦ y ≦ 0.5, and 0.5 ≦ z ≦ 1.5, respectively. The metal oxide is Li _{2- x} Mo ₁ O _z PO _Four , Li _{2- x} Mo _{1- y} Fe _y O _z PO _Four , Li _{2- x} Mo ₁ O _z GeO _Four , Li _{2- x} Mo _{1- y} Ru _y O _z PO _Four Or Li _{2- x} M (consists of Mo and Ti) ₁ O _z PO _Four The nonaqueous electrolyte secondary battery according to claim 1, wherein

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