JP3627516B2 - Non-aqueous secondary battery - Google Patents

Description

【００６９】
実施例２
比較用の負極材料として、平均粒径１０μｍの多結晶ケイ素を用いる以外は上記と同様にして負極合剤ペーストを作成し負極シート（比較例−１）を作製し電池４５とした。また、粒径２μｍの多結晶ケイ素を用い、負極合剤の該ケイ素と鱗片状黒鉛の添加重量比を８０：２０にした以外は上記と同様にして負極シート（比較例−２）を作製し電池４６とした。更に負極材料としてメソフェーズピッチコークスを用い、導電補助剤としてアセチレンブラックを２重量％加えた以外は同様にして負極シート（比較例−３）を作製し電池４７とした。これらの電池を用いて、電池１から４４と同様な試験を実施した。
表２にこれらの比較電池について得られた充放電性能の結果を示す。
【００７０】

【００７１】
本発明の化合物を用いた実施例−１の電池を比較すると、正極活物質中に不純物として含まれるアルカリ土類元素あるいは硫黄の量が本発明の範囲を超える例においてはサイクル寿命が低下し性能劣化が加速されることが明らかである。また、実施例−１の電池と比較例−１の電池性能を比較すると、負極材料の平均粒子サイズの小さな化合物はサイクル寿命に優れていることがわかる。さらに、実施例−１で比較すると、合金、リチウムケイ化物からリチウムを除去したケイ素、コロイダルシリカを付着させたケイ素、メッキにより金属を被覆したケイ素、ポリフッ化ビニリデンにて被覆したケイ素は何も処理を施さないケイ素よりサイクル寿命が改良されている。
さらに、負極材料において本発明の処理を組み合わせることにより、単独処理の負極材料に比較してサイクル寿命が改良されている。
また、比較例−３から本発明の負極材料を用いた電池は負極に炭素質材料を用いたものに比べて放電容量が高い。
以上の結果は、正極活物質にＬｉＮｉＯ_２ 系酸化物やＬｉＭｎ_２ Ｏ_４ 系酸化物に代えてＬｉＣｏＯ_２ およびＬｉＣｏ_１．９２Ｓｎ_０．０８Ｏ_２ を用いた場合も同様な効果が得られた。
【００７２】
【発明の効果】
本発明によれば、放電容量とエネルギー量を高め、サイクル寿命の向上した非水二次電池を得ることができる。
【図面の簡単な説明】
【図１】実施例に使用したシリンダー電池の断面図を示したものである。
【符号の説明】
１ 負極を兼ねる電池缶
２ 巻回電極群
３ 上部絶縁板
４ 正極リード
５ ガスケット
６ 正極端子を兼ねる電池蓋
６１ 圧力感応弁体
６２ 電流遮断素子（スイッチ）
６３ ＰＴＣ素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous lithium secondary battery using a silicon compound for a negative electrode and having a high capacity and a long cycle life.
[0002]
[Prior art]
In a lithium secondary battery using a negative electrode material not containing lithium metal and a positive electrode active material containing lithium, first, lithium contained in the positive electrode active material is inserted into the negative electrode material to increase the activity of the negative electrode material. This is a charging reaction, and the reverse reaction is a reaction in which lithium ions are inserted into the positive electrode active material from the negative electrode material. Carbon is used as this type of lithium battery negative electrode material. Carbon (C₆The theoretical capacity of Li) is 372 mAh / g, and further high capacity negative electrode materials are desired. On the other hand, it is well known that the theoretical capacity of silicon forming an intermetallic compound with lithium exceeds 4000 mAh / g and is larger than that of carbon. For example, Japanese Patent Laid-Open No. 5-74463 discloses single crystal silicon, and Japanese Patent Laid-Open No. 7-29602 discloses amorphous silicon. In the case of an alloy containing silicon, examples in which silicon is contained in a Li-Al alloy are disclosed in JP-A-63-66369 (19% by weight of silicon) and 63-174275 (0.05 to 1.0% by weight of silicon). No. 63-285865 (silicon is 1 to 5% by weight). However, since these alloy patent applications are mainly composed of lithium, a compound containing no lithium has been used for the positive electrode active material. JP-A-4-109562 discloses an alloy containing 0.05 to 1.0% by weight of silicon. Japanese Patent Laid-Open No. 62-226563 discloses a method of mixing a metal that can be alloyed with lithium and graphite powder. However, both have poor cycle life and have not yet been put to practical use. The reason why the cycle life of silicon is inferior is presumed that its electronic conductivity is low, the volume expands due to lithium insertion, and the particles are pulverized.
In addition, as a positive electrode active material of a general-purpose 4V class lithium ion secondary battery, LiCoO₂  LiCo_1-xNi_xO₂  , LiNiO₂  , LiNi_1-xM_xO₂  , LiMn₂  O₄  , LiMn_2-xM_xO₄Layered compounds capable of inserting and releasing Li, such as (M is one or more metal cations), are used. Among these, especially LiCoO disclosed in JP-A-55-136131.₂  Is 3.5 Vvs. It is commercialized quickly because it gives a high charge / discharge potential higher than Li and has a long cycle life. On the other hand, the development of secondary batteries using Mn or Ni has been activated in place of Co, which has a limited resource supply and high cost. As disclosed in JP-A-6-096769, JP-A-6-267539, etc., Ni-based secondary batteries are characterized by a higher current capacity than Co-based batteries. In addition to being the cheapest of the three types of metal oxides, Mn-based oxides are characterized by high average voltage and excellent safety. These Ni-based and Mn-based active materials, however, are affected by the occurrence of Yang-Teller distortion, etc.₂Since the crystal structure is electrochemically unstable in comparison with the above, the inferior cycle life of charge / discharge is a major countermeasure for practical application. Especially in the case of Ni, the reduced Ni trivalent is more stable than Co._xNiO₂In (x ≦ 1), the oxidation-reduction potential becomes low, and the capacity deterioration is significant in repeated charging cycles in which the average charge of Ni exceeds 4 V approaching tetravalent. Therefore, as disclosed in JP-A-63-2111565, JP-A-5-242891, JP-A-8-213015, etc., a method of stabilizing cycle life and increasing potential by adding Co or other metal cations to Ni. Is commonly used. In Mn, in addition to the occurrence of Yang-Teller distortion on the discharge side with a high Li content, the elution of Mn trivalent on the charge side deteriorates the cycle characteristics. A method of stabilizing the cycle life and increasing the potential by adding a metal cation is used. However, these metal-doped positive electrode active materials vary in cycle performance and storage stability due to differences in the purity of the synthetic raw material including the raw material of the doping element (D) and the purification conditions even if the charged composition ratio is the same. Therefore, it is necessary to construct a technology for stabilizing the performance including the control of the purity of the positive electrode active material.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to increase the energy amount of a lithium secondary battery and to stably maintain charge / discharge characteristics including a cycle life.
[0004]
[Means for Solving the Problems]
An object of the present invention is to provide a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a non-aqueous secondary battery including non-aqueous electrolytes, and the negative electrode material contains silicon atoms capable of inserting and releasing lithium. A positive electrode active material,, Li _x M _1-y D _y O _ba X _a (M is Ni or Co, D is one or more selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P) X is a halogen element, and is represented by a composition of 0.2 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) Lithium-containing cobalt composite oxide or lithium-containing nickel composite oxide, or Li _x Mn _2-y D _y O _ba X _a (D is one or more elements selected from Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.05 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 3.5 ≦ b ≦ 4.5, 0 ≦ a ≦ 1.0) StuffA non-aqueous secondary battery characterized in that the content of alkaline earth element in the positive electrode composite oxide is 0.1 wt% or less and the content of sulfur is 0.1 wt% or less It was solved.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Although the aspect of this invention is demonstrated below, this invention is not limited to these.
(1) In a non-aqueous secondary battery in which a non-aqueous secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a non-aqueous electrolyte, the negative electrode material can insert and release lithium. A compound containing a silicon atom, and the positive electrode active material is, Li _x M _1-y D _y O _ba X _a (M is Ni or Co, D is one or more selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P) X is a halogen element, and is represented by a composition of 0.2 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) Lithium-containing cobalt composite oxide or lithium-containing nickel composite oxide, or Li _x Mn _2-y D _y O _ba X _a (D is one or more elements selected from Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.05 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 3.5 ≦ b ≦ 4.5, 0 ≦ a ≦ 1.0) StuffThe alkaline earth element content in the positive electrode composite oxide is 0.1% by weight or less, and the sulfur content is 0.1% by weight or less.
(2) The average particle size of the silicon compound of item (1) is 0.01 to 50 m.
(3) The silicon compound of item (1) is an alloy.
(4) In the alloy of item (3), at least one metal other than silicon is an alkaline earth metal, a transition metal, or a semimetal.
(5) At least one of the metals of the items (3) and (4) is Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, Zn.
(6) The weight ratio of the metal to silicon in the items (3) to (5) is 5 to 90%.
(7) The silicon compound of item (1) is silicon obtained by removing a metal from a metal silicide.
(8) The metal silicide of item (7) is lithium silicide.
(9) The lithium content of the lithium silicide of item (8) is 100 to 420 atomic% with respect to silicon.
(10) The silicon compound of item (1) adheres to a ceramic that does not react with lithium.
(11) The ceramic of (10) is Al₂ O_Three , SiO₂ TiO₂ , SiC, Si_Three N_Four At least one selected from
(12) The weight ratio of the ceramic to the silicon compound of items (10) and (11) is 2 to 50%.
(13) A method for attaching the ceramic to the silicon compound of (10) to (12), comprising a step of heating to 300 to 1300 ° C.
(14) The silicon compound of item (1) is at least coated with a metal.
(15) The method of coating with the metal of (14) is an electroless plating method, a vapor deposition method, a sputtering method, or a chemical vapor deposition method.
(16) At least one of the metals to be coated according to items (14) and (15) is Ni, Cu, Ag, Co, Fe, Cr, W, Ti, Au, Pt, Pd, Sn, or Zn.
(17) The specific conductivity of the silicon compound coated with the metal of (14) to (16) is 10 times or more the specific conductivity of the uncoated silicon compound.
The silicon compound of item (18) (1) is previously coated with a thermoplastic resin.
(19) The thermoplastic resin of item (18) is polyvinylidene fluoride or polytetrafluoroethylene.
[0006]
(20) The weight ratio of the thermoplastic resin to the silicon compound of items (18) and (19) is 2 to 30%.
(21) The coverage of the thermoplastic resin of items (18) to (20) is 5 to 100%.
(22) Carbon exists in an amount of 5 to 1900% by weight with respect to the silicon compound of item (1).
(23) The carbon of item (22) is scaly natural graphite.
(24) The charge / discharge range of the silicon compound of item (1) is expressed as Li equivalent ratio of lithium inserted into and released from silicon._x When represented by Si, x is in the range of 0 to 4.2.
(25) The charge / discharge range of the silicon compound of item (1) is Li_x When represented by Si, x is in the range of 0 to 3.7.
The positive electrode active material in (26) (1) isGoodPreferably, Li_x Ni_1-y D_y O_ba X_a (D is one or more elements selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) It is a thing.
[0007]
(28) The content of alkaline earth element in the lithium-containing composite oxide of the positive electrode is 0.04% by weight or less, and the content of sulfur is 0.04% by weight or less.
(29) The water content in the lithium-containing composite oxide of the positive electrode is 0.5% by weight or less.
(30) The content of the alkaline earth element in the lithium-containing composite oxide of the positive electrode is 0.02% by weight or less, and the content of sulfur is 0.02% by weight or less.
(31) The water content in the lithium-containing composite oxide of the positive electrode is 0.2% by weight or less.
(32) The average particle size of silicon used in the items (3) to (25) is 0.01 to 50 μm.
The silicon mentioned here is a silicon simple substance, a silicon alloy, or a silicide that can react with lithium.
(33) The ceramics of the items (7) to (13) are adhered to the alloys of the items (3) to (6).
(34) The metal of the items (14) to (17) is coated on the alloy of the items (3) to (6).
(35) The metal of the items (14) to (17) is coated on the material of the item (33).
(36) The thermoplastic resin of items (18) to (21) is coated on the alloy of items (3) to (6).
(37) The material of items (33) to (35) is coated with the thermoplastic resin of items (18) to (21).
(38) The carbons of the items (22) and (23) are allowed to coexist in the alloys of the items (3) to (6).
(39) The carbons of the items (22) and (23) are allowed to coexist in the materials of the items (33) to (37).
[0008]
(40) The alloys of items (3) to (6) are used in the charge / discharge ranges of items (24) and (25).
(41) The materials of items (33) to (39) are used in the charge / discharge range of items (24) and (25).
(42) The compound of item (26) is used as the positive electrode active material of the alloy negative electrode of items (3) to (6).
(43) The compound of item (26) is used as the positive electrode active material of the material of items (33) to (39).
(44) The ceramics of items (7) to (13) are adhered to the silicon of items (7) to (9).
(45) The silicon of items (14) to (17) is coated on the silicon of items (7) to (9).
(46) The material of item (39) is coated with the metal of items (14) to (17).
(47) The thermoplastic resin of items (18) to (21) is coated on the silicon of items (7) to (9).
(48) The material of items (44) to (46) is coated with the thermoplastic resin of items (18) to (21).
(49) The carbons of the items (22) and (23) are allowed to coexist with the silicon of the items (7) to (9).
(50) The carbons of the items (22) and (23) are allowed to coexist in the materials of the items (44) to (48).
(51) The silicon of items (7) to (9) is used in the charge / discharge range of items (24) and (25).
(52) The materials of items (44) to (50) are used in the charge / discharge ranges of items (24) and (25).
(53) The compound of item (26) is used as the positive electrode active material of the silicon negative electrode of items (7) to (9).
(54) The compound of item (26) is used as the positive electrode active material of the negative electrode of items (44) to (50).
(55) The metal of (14) to (17) is coated on the silicon compound of items (10) to (13).
(56) The thermoplastic resin of (18) to (21) is coated on the silicon compound of items (10) to (13).
(57) The material of item (50) is coated with the thermoplastic resin of items (18) to (21).
(58) The carbons of the items (22) and (23) are allowed to coexist in the silicon compounds of the items (10) to (13).
(59) The carbons of the items (22) and (23) are allowed to coexist in the materials of the items (55) to (57).
[0009]
(60) The silicon compound of the items (10) to (13) is used in the charge / discharge range of the items (24) and (25).
(61) The materials of items (55) to (57) are used in the charge / discharge ranges of items (24) and (25).
(62) The compound of item (26) is used as the positive electrode active material of the silicon compound negative electrode of items (10) to (13).
(63) Items (55) to (57) The compound of item (26) is used as the positive electrode active material of the negative electrode.
(64) The ceramics of items (7) to (13) are adhered to the materials of items (14) to (17).
(65) The material of items (14) to (17) is coated with the thermoplastic resin of items (18) to (21).
(66) The thermoplastic resin of items (18) to (21) is coated on the material of item (64).
(67) The carbons of the items (22) and (23) are allowed to coexist in the materials of the items (14) to (17) and (64) to (66).
(68) The materials of items (14) to (17) and (64) to (67) are used in the charge / discharge ranges of items (24) and (25).
(69) Item (14)-(17), (64)-(67) The compound of item (26) is used as the positive electrode active material of the negative electrode.
[0010]
(70) The ceramics of the items (7) to (13) are adhered to the materials of the items (18) to (21).
(71) The materials of items (14) to (17) are coated on the materials of items (18) to (21) and (70).
(72) The carbons of the items (22) and (23) are allowed to coexist in the materials of the items (18) to (21), (70), and (71).
(73) The materials of items (18) to (21) and (70) to (71) are used in the charge / discharge range of items (24) and (25).
(74) Items (18) to (21), (70) to (71) The compound of item (26) is used as the positive electrode active material of the negative electrode.
(75) The compound of item (26) is used as the positive electrode active material of the negative electrode of items (22) and (23).
[0011]
The positive electrode (or negative electrode) used in the present invention can be prepared by coating and molding a positive electrode mixture (or negative electrode mixture) on a current collector. The positive electrode mixture (or negative electrode mixture) includes a positive electrode active material (or negative electrode material), a conductive agent, a binder, a dispersant, a filler, an ionic conductive agent, a pressure enhancer, and various additives. it can. These electrodes may be disk-shaped or plate-shaped, but are preferably flexible sheets.
[0012]
The configuration and materials of the present invention are described in detail below.
The compound containing a silicon atom capable of inserting and releasing lithium used in the negative electrode material of the present invention means a silicon simple substance, a silicon alloy, or a silicide. As the silicon simple substance, any of single crystal, polycrystal, and amorphous can be used. The purity of the simple substance is preferably 85% by weight or more, and particularly preferably 95% by weight or more. Furthermore, 99 weight% or more is especially preferable. The average particle size is preferably 0.01 to 50 μm. In particular, 0.02 to 30 μm is preferable. Furthermore, 0.05-5 micrometers is preferable.
[0013]
The silicon alloy is considered to be effective because it suppresses pulverization due to expansion and contraction of silicon that occurs when lithium is inserted and released, and improves the low conductivity of silicon. As the alloy, an alloy with an alkaline earth metal, a transition metal, or a metalloid is preferable. In particular, a solid solution alloy or a eutectic alloy is preferable. A solid solution alloy is an alloy that forms a solid solution. For example, an alloy of Ge is a solid solution alloy. An eutectic alloy is an alloy that is eutectic with silicon in any proportion, but the solid obtained by cooling is a mixture of silicon and metal. Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, and Zn form a eutectic alloy.
Among these, alloys of Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, and Zn are more preferable. Two or more of these alloys are also preferred. In particular, an alloy containing Ge, Ag, Al, Cd, In, Sb, Sn, and Zn is preferable.
The mixing ratio of these alloys is preferably 5 to 70% by weight with respect to silicon. 10 to 60 weight% is especially preferable. In this case, electrical conductivity is improved, but in terms of battery performance, in particular, discharge capacity, high rate characteristics, and cycle life, the specific conductivity may be 10 times or more that of silicon or a silicon compound before the alloy. preferable. The average particle size of the alloy is preferably 0.01 to 40 μm. In particular, 0.03 to 5 μm is preferable.
[0014]
Silicide refers to a compound of silicon and metal. As silicide, CaSi, CaSi₂, Mg₂Si, BaSi₂, SrSi₂, Cu₅Si, FeSi, FeSi₂CoSi₂, Ni₂Si, NiSi₂, MnSi, MnSi₂, MoSi₂, CrSi₂TiSi₂, Ti₅Si₃, Cr₃Si, NbSi₂, NdSi₂, CeSi₂, SmSi₂, DySi₂, ZrSi₂, WSi₂, W₅Si₃, TaSi₂, Ta₅Si₃, TmSi₂, TbSi₂, YbSi₂, YSi₂, YSi₂, ErSi, ErSi₂, GdSi₂, PtSi, V₃Si, VSi₂, HfSi₂, PdSi, PrSi₂, HoSi₂, EuSi₂LaSi, RuSi, ReSi, RhSi, etc. are used.
[0015]
As the silicon compound, silicon obtained by removing metal from a metal silicide can be used. Examples of the shape of silicon include fine particles having a size of 1 μm or less and porous particles, and fine particles aggregated to form porous secondary particles. The reason why the cycle life is improved when silicon is used is considered to be difficult to pulverize. The metal of the metal silicide is preferably an alkali metal or an alkaline earth metal. Of these, Li, Ca, and Mg are preferable. In particular, Li is preferable. The lithium content of the lithium silicide is preferably 100 to 420 mol% with respect to silicon. 200-420 is particularly preferable. The method of removing alkali metal or alkaline earth metal from the alkali metal or alkaline earth metal silicide is preferably treated with a solvent that reacts with the alkali metal or alkaline earth metal and dissolves the reaction product. . As the solvent, water and alcohols are preferable. In particular, degassed and dehydrated alcohols are preferred. Examples of alcohols include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, t-butyl alcohol, 1-pentyl alcohol, 2-pentyl alcohol, and 3-pentyl alcohol. Is preferred. In particular, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, and t-butyl alcohol are preferable. The removal of Ca and Mg is preferably water. It is more preferable to use a pH buffering agent that keeps it near neutrality.
[0016]
It is considered that the ceramic adhered to the silicon compound is effective for suppressing silicon fine powder. As the ceramic, a compound which does not react with lithium in principle is preferable. In particular, Al₂O₃, SiO₂TiO₂, SiC, Si₃N₄Is preferred.
As a method for adhering silicon and ceramic, mixing, heating, vapor deposition, and CVD are used, but the combined use of mixing and heating is particularly preferable. In particular, Al₂O₃And SiO₂After the sol and silicon are dispersed and mixed, the mixture is heated and the solid solution is pulverized to obtain silicon and Al.₂O₃And SiO₂Can be obtained. In this case, Al₂O₃And SiO₂The deposits of Al₂O₃And SiO₂Etc. The surface is covered with silicon powder, Al₂O₃And SiO₂It is confined inside a lump or the like, or the surface of silicon is covered. Mixing and dispersing can be achieved by mechanical stirring, ultrasonic waves, and kneading. Heating is preferably performed in the range of 300 ° C to 1300 ° C in an inert gas, but 500 ° C to 1200 ° C is particularly preferable. Inert gases include argon, nitrogen, and hydrogen. These mixed gases are also used. As the pulverization method, well-known methods such as a ball mill, a vibration mill, a planetary ball mill, and a jet mill are used. This pulverization is also preferably performed in an inert gas. The mixing ratio of ceramics to silicon is preferably in the range of 2 to 50% by weight, particularly 3 to 40%.
The average particle size determined from the electron microscope observation of silicon is preferably 0.01 to 40 μm. In particular, 0.03 to 5 μm is preferable.
[0017]
The metal coating of the silicon compound of the present invention includes electroplating, displacement plating, electroless plating, resistance heating vapor deposition, electron beam vapor deposition, cluster ion vapor deposition and other vapor deposition methods, sputtering methods, and chemical vapor deposition methods. (CVD method). In particular, an electroless plating method, a resistance heating vapor deposition method, an electron beam vapor deposition method, a cluster ion vapor deposition method or the like, a sputtering method, or a CVD method is preferable. Furthermore, an electroless plating method is particularly preferable. The electroless plating method is described in “Electroless Plating Basics and Applications” published by Nikkan Kogyo Shimbun (1994). The reducing agent is preferably a phosphinate, phosphonate, borohydride, aldehyde, saccharide, amine, or metal salt. Sodium hydrogen phosphinate, sodium hydrogen phosphonate, sodium borohydride, dimethylamine borane, formaldehyde, sucrose, dextrin, hydroxylamine, hydrazine, ascorbic acid, and titanium chloride are preferred. In addition to the reducing agent, the plating solution preferably contains a pH adjusting agent and a complexing agent. Also for these, the compounds described in “Electroless plating basics and applications” are used. The pH of the plating solution is not particularly limited, but 4 to 13 is preferable. The temperature of the liquid is preferably 10 ° C to 100 ° C, but 20 ° C to 95 ° C is particularly preferable. In addition to the plating bath, SnCl₂Activation bath consisting of aqueous hydrochloric acid, PdCl₂A nucleation bath composed of an aqueous hydrochloric acid solution is used, and a filtration step, a water washing step, a pulverization step, and a drying step are further used.
[0018]
Moreover, as a form of the silicon compound to be coated, any of powder, block, plate and the like is used. The metal to be coated may be anything as long as it is a highly conductive metal, but Ni, Cu, Ag, Co, Fe, Cr, W, Ti, Au, Pt, Pd, Sn, and Zn are particularly preferable. In particular, Ni, Cu, Ag, Co, Fe, Cr, Au, Pt, Pd, Sn, and Zn are preferable, and Ni, Cu, Ag, Pd, Sn, and Zn are particularly preferable. The amount of metal to be coated is not particularly limited, but it is preferable to coat so that the specific conductivity is 10 times or more of the specific conductivity of the silicon compound as the base.
[0019]
The silicon compound used in the present invention is preferably coated with a thermoplastic resin. As the thermoplastic resin, a fluorine-containing polymer compound, an imide polymer, a vinyl polymer, an acrylate polymer, an ester polymer, polyacrylonitrile, or the like is used. In particular, the thermoplastic resin is preferably a resin that does not easily swell in the electrolytic solution. Specific examples include water-soluble polymers such as polyacrylic acid, polyacrylic acid Na, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic acid copolymer, Polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, and (meth) acrylic acid esters such as 2-ethylhexyl acrylate (Meth) acrylic acid ester copolymer, (meth) acrylic acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer Examples thereof include emulsions (latex) or suspensions of coalesced polybutadiene, neoprene rubber, fluoro rubber, polyethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, phenol resin, epoxy resin and the like. In particular, polyacrylate ester latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are exemplified.
These compounds can be used alone or in combination. In particular, a fluorine-containing polymer compound is preferable. Of these, polytetrafluoroethylene and polyvinylidene fluoride are preferred. As a method for coating in advance, a thermoplastic resin is dissolved in a solvent, and a silicon compound is mixed and kneaded in the solution. A method of drying the solution and pulverizing the obtained solid is preferred. As a usage-amount of the thermoplastic resin with respect to a silicon compound, 2 to 30 weight% is preferable. In particular, 3 to 20% by weight is preferable. The coverage is preferably 5 to 100%, particularly preferably 5 to 90%. The average particle size of the coated particles is preferably 0.01 μm to 40 μm. In particular, 0.03 to 5 μm is preferable.
[0020]
In the present invention, it is preferable to use a mixture of a silicon compound and a carbonaceous compound. As the carbonaceous material, a material used for a conductive agent or a negative electrode material is used. Examples of the carbonaceous material include non-graphitizable carbon materials and graphite-based carbon materials. Specifically, carbon materials having surface spacing, density, and crystallite size described in JP-A-62-122066, JP-A-2-66856, JP-A-3-245473, etc. A mixture of natural graphite and artificial graphite described in Japanese Patent No. -290844, and vapor-grown carbon materials described in Japanese Patent Laid-Open Nos. 63-24555, 63-13282, 63-58763, and Japanese Patent Laid-Open No. 6-212617 A material obtained by heating and baking non-graphitizable carbon described in JP-A-5-182664 at a temperature exceeding 2400 ° C. and having a peak of X-ray diffraction corresponding to a plurality of 002 planes, No. 307957, JP-A-5-307958, JP-A-7-85862, and JP-A-8-315820, a mesophase carbon material synthesized by pitch firing described in JP-A-6-84516 Graphite with the above coating layer, various granular materials, microspheres, flat bodies, microfibers, whisker-shaped carbon materials, phenolic resins, acrylonitrile resins, furfuryl alcohol resin fired bodies, hydrogen atoms Examples thereof include carbon materials such as polyacene material.
Furthermore, specific examples of the conductive agent include natural graphite such as scaly graphite, scaly graphite, and earthy graphite, high-temperature fired bodies such as petroleum coke, coal coke, celluloses, saccharides, and mesophase pitch, and vapor-grown graphite. Graphite such as artificial graphite, carbon black such as acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, carbon materials such as asphalt pitch, coal tar, activated carbon, mesofuse pitch, polyacene preferable. These may be used singly or as a mixture.
[0021]
In particular, the carbon material described in JP-A-5-182664, various granular materials, microspheres, flat plate bodies, fibers, whisker-shaped carbon materials, and mesophase pitch, phenol resin, acrylonitrile resin fired bodies, Furthermore, a polyacene material containing a hydrogen atom is preferable.
Of these, scaly natural graphite is preferable because it makes the mixture film strong.
The mixing ratio is preferably 5 to 1900% by weight with respect to the silicon compound. In particular, 20 to 500% by weight is preferable. Furthermore, 30 to 400% by weight is preferable.
As the conductive agent, a metal other than carbon can be used. Ni, Cu, Ag, and Fe are preferable.
[0022]
The charge / discharge range of the silicon compound negative electrode material is preferably x = 0 to 4.2 when the ratio of lithium and silicon atoms that can be inserted and released is represented by LixSi. As a result of intensive studies on improving the cycle life of silicon, it was found that the cycle life is greatly improved when x is kept in the range of 0 to 3.7. The charge potential was 0.0 V, including overvoltage, at x = 4.2 against the lithium metal counter electrode, whereas it was about 0.05 V at x = 3.7.
At this time, the shape of the discharge curve changes, and a flat discharge curve is obtained in the vicinity of 0.5 V (body lithium metal) at 0.0 V charge folding, whereas it is 0.05 V or more, particularly 0.08 V or more (x = 3.6), a gentle curve with an average voltage of about 0.4V is obtained. That is, it shows that a specific phenomenon in which the discharge potential is lowered when the voltage at the end of charging is increased and a reversibility of the charge / discharge reaction is also found.
[0023]
Although the method having the effect of improving the cycle life while maintaining the high capacity of the silicon compound has been individually described, a more preferable embodiment is that a further improved effect can be obtained by combining each of the above methods. I found it.
In the present invention, as a negative electrode material, a compound capable of inserting and releasing lithium, such as a carbonaceous material, an oxide material, a nitride material, a sulfide material, lithium metal, and a lithium alloy, which are other negative electrode materials, with respect to the silicon compound of the present invention Can be combined.
[0024]
Used in the present inventionPositiveThe composition of the active material is Li_x M_1-y D_y O_ba X_a (M is Ni or Co, D is one or more selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P) X is a halogen element, and is represented by a composition of 0.2 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) Lithium-containing cobalt composite oxide or lithium-containing nickel composite oxide. Of these, Li is particularly preferable._x Ni_1-y D_y O_ba X_a (D is one or more elements selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) It is a thing. Also,Used in the present inventionThe composition of the positive electrode active material is Li_x Mn_2-y D_y O_ba X_a (D is one or more elements selected from Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P, and X is a halogen element. 0.05 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 3.5 ≦ b ≦ 4.5, 0 ≦ a ≦ 1.0) It is a thing. In the above-described general formula of the positive electrode active material, D is a transition element (Co, Ni, Mn) of the central metal or one or more metal or metalloid elements substituting for a part of Li. This is an element that contributes to improvement of battery performance such as increase of discharge average voltage and improvement of cycle life. Specific examples of positive electrode active materialsExampleAs Li_x CoO₂ , Li_x NiO₂ , Li_x MnO₂ , Li_x Co_1-y Ni_y O₂ , Li_x Co_1-y V_y O_z , Li_x Co_1-y Fe_y O₂ , Li_x Mn₂ O_Four , Li_x Mn_2-y Co_y O_Four , Li_x Mn_2-y Ni_y O_Four , Li_x Mn_2-y V_y O_Four , Li_x Mn_2-y Fe_y O_Four (Where x = 0.2 to 1.2, y = 0.1 to 0.9, z = 2.01 to 2.3). Among these, examples of preferable compositions include Li_x Ni_1-y Co_y O₂ , Li_x Ni_1-y Al_y O₂ , Li_x Ni_1-y Co_y O_2-b F_b , Li_x Ni_1-y B_y O₂ , Li_x Mn₂ O_Four , Li_x Mn_2-y Al_y O_Four , Li_x Mn_2-y Co_y O_Four , Li_x Mn_2-y Fe_y O_Four (X = 0.2 to 1.2, y = 0.1 to 0.3, b = 0 to 0.3). Here, the value of x is a value before the start of charging / discharging, and increases or decreases beyond the above range due to charging / discharging.
[0025]
Next, each of the Ni-based oxide and the Mn-based oxide preferably used as the positive electrode active material will be described.
The preferred composition of the Ni oxide-based positive electrode active material is Li_xNi_1-yD_yO_baX_aIndicated by Here, what can be used as D is usually one or more elements selected from Group 13 and Group 14 elements and transition metal elements of the periodic table, and preferably D is Co, Cr, Fe, Cu, Zn , Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P are one or more elements. X is a halogen element. The amount of these elements in the composition ranges from 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0. It is. Of these, one of the preferred compositions is Li_xNi_1-yM_yO_b(M is one or more elements selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P, 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3).
Further, another preferable composition of the Ni oxide-based positive electrode active material is a composition in which fluorine is substituted as X, and Li_xNi_1-yM_yO_baF_a(M is one or more elements selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P, 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 <a ≦ 1.0).
Particularly preferred as the composition of the positive electrode active material of the present invention is a structure containing cobalt which is effective for improving the discharge potential as M, and further containing a group M of elements which are effective as structural reinforcing elements._xNi_1-yzCo_yM_zO_baF_a(M is one or more elements selected from Mn, Cr, Fe, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, 0.2 <x ≦ 1.2, 0.05 ≦ y ≦ 0.5, 0.01 ≦ z ≦ 0.3, 0 ≦ a ≦ 1.0, 1.8 ≦ b ≦ 2.3) It is a complex oxide.
[0026]
As the Mn-based positive electrode active material, A [B₂  ] O₄  Type LiMn with spinel structure₂  O₄  It is a system oxide. This type of oxide includes LiMn₂O₄For example, the general formula Li_{1 + x}[Mn_2-y] O₄  A compound having a non-stoichiometric composition and a structure including a defect represented by (0 <x <1.7, 0 ≦ y <0.7) is also included. As an example of this, Li₄  Mn₅  O₁₂Alternatively, Li [Li_1/3Mn_5/3] O₄  Is mentioned. Another preferred example is the general formula Li_1-x[Mn_2-y] O₄  (0 <x <1.0, 0 ≦ y <0.5). Examples of this include Li which is a non-stoichiometric spinel compound disclosed in, for example, JP-A-4-240117.₂  Mn₅  O₁₁Or in the spinel structure display_1-x[Mn_2-y] O₄  (X = 0.273, y = 0.182). Another preferred structure is the general formula Li_1-x[Mn_2-y] O₄(0 <x ≦ 0.20, 0 <y <0.4), for example, Li₂  Mn₄  O₉  Is mentioned.
Similarly to the Ni-based oxide, a Mn-based composite oxide having a composition in which a metal other than Mn or a half-metal cation is used as another element for the purpose of improving cycle performance is also preferable. As other elements, trivalent metal elements such as Co, Al, Cr and Fe are most preferable, and examples of active material compositions containing these are described in JP-A-9-245896.
[0027]
LiNiO added with other metal elements₂Or LiMn₂O₄Is synthesized by heat treatment using compounds (oxides or salts) each containing various metals added to the compound that is a Ni or Mn raw material and the Li compound that is a Li raw material. Since the compound is used, it is usually difficult to produce the final active material with high purity, and different kinds of materials such as Na, K, Mg, Ca, Al, sulfur, Cu, Fe, and Si derived from these metal compound raw materials are used. Elements are likely to be mixed into the positive electrode active material as impurities. These impurities may cause deterioration of the cycle life or high temperature storage stability of the battery due to the effect of elution into the non-aqueous electrolyte during charging / discharging. Therefore, it is preferable to reduce these impurities below a certain level in order to stabilize the performance.
[0028]
The present inventor has found that, among the above-mentioned impurity elements, particularly alkaline earth metals and sulfur, the storage characteristics of the battery can be improved by limiting the level of contamination within a specified amount. That is, in the active material containing these elements as impurities at the same time, for example, the acidity is locally reduced on the surface of the active material in contact with the electrolytic solution, and the metal element is eluted in the electrolytic solution, resulting in a change in performance of the positive electrode or the negative electrode. Problems arise. This phenomenon is a serious problem because it accelerates the decrease in acidity especially in the situation where moisture is present in the active material or the electrolyte.
Specifically, the alkaline earth element content in the positive electrode active material is 0.1% by weight or less, the sulfur content is 0.1% by weight or less, and the water content is 0.5 or less. And effective in improving cycle life. Effective contents for improving the performance include an alkaline earth element content of 0.04% by weight or less, a sulfur content of 0.04% by weight or less, and a moisture content of 0.2% by weight or less. Furthermore, it is more effective that the alkaline earth element content is 0.02% by weight or less, the sulfur content is 0.02% by weight or less, and the water content is 0.1% by weight or less. Most preferably, the alkaline earth element content is 0.02% by weight or less, the sulfur content is 80 ppm or less (0.008% or less) by weight, and the water content is 0.1% by weight or less.
[0029]
Among the alkaline earth elements referred to in the present invention, those whose content management is important for improving battery performance are magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Of these, magnesium (Mg), calcium (Ca), and barium (Ba) are important, and calcium (Ca) is particularly important.
[0030]
Sulfur is a sulfate radical (SO) contained in the raw material for firing.₄) And the like are often mixed as impurities, and the content of 0.1% or less is effective in improving storage stability, preferably 0.04% or less, more preferably 0.02% or less. The effect is great. The sulfur content is 80 ppm or less which is most effective for improving the performance.
[0031]
The synthesis of the composite oxide for the positive electrode of the present invention includes a lithium compound that is a lithium raw material and a metal compound that is a raw material of Co, Ni, or Mn, and optionally B, Al, Cr, Sn, Si, Fe, Ti. A compound containing other element D typified by, for example, is mixed and the raw material powder is baked in a high-temperature dry state, or by a chemical reaction in a solution state typified by a sol-gel method.
Lithium raw materials include LiOH and Li₂  CO₃  , Li₂  O, LiNO₃  , Li₂  SO₄  , LiHCO₃  , Li (CH₃  COO), alkyl lithium and the like are used, and Ni raw materials include NiO and NiCO.₃  , Ni (NO₃  )₂  , Ni powder, NiCl₂  , NiSO₄  , Ni₃  (PO₄  )₂  , Ni (CH₃  COO)₂  , Ni (OH)₂NiOOH, Ni alkoxide, etc. are useful. In addition, as a raw material for the other element M, Co₂  O₃  , Co₃  O₄  , CoCO₃  , Co (NO₃  )₂  CoCl₂  , MnCO₃  , MnO₂  , Mn (NO)₃  , B₂  O₃  , B (OH)₃  , Al₂  O₃  , Al (NO₃  )₃  , Al (OH)₃  , SnO₂  , SnO, SnCl₂, Sn alkoxide, SiO₂  , SiO, alkoxysilane, Fe₂  O₃  , FeCl₃  , FeOOH, Fe (NO₃  )₃  TiO₂  , GeO₂  , ZrO₂  , Nd₂  O₃  , La₂  O₃  , La₂  O₃  , Zn (NO₃  )₂  , WO₃  , Ga (NO₃  )₂  , CuO, V₂  O₅  , Sm₂  O₃  , Y₂  O₃  , AlF₃  , LiF, LaF₃  , SnF₂  , Li₃  PO₄  , AlPO₄  Etc. can be used. These raw materials may be mixed as a solid powder, or a plurality of raw materials may be dissolved in a solvent to form a mixed solution, which may be dried, solidified, or made into a mixture as a slurry. In the case of synthesizing by firing, the above raw material powder or slurry mixture is preferably used at a temperature of 400 ° C. to 1000 ° C., preferably 600 ° C. to 900 ° C. in the presence of oxygen or an oxygen partial pressure of 0.2 atm or higher. The synthesis is carried out by reacting for 4 to 48 hours in an atmosphere having an oxygen partial pressure of 0.5 or more. Firing is repeated a plurality of times under the same conditions or under different conditions as necessary. The raw material mixture may be previously filled in a pellet and molded. Examples of the firing method include powder mixing methods described in JP-A-62-264560, JP-A-2-40861, JP-A-6-267538, and JP-A-6-231767, JP-A-4-237793, JP-A-5-325966, and JP-A-6-208334. The solution mixing method described in JP-A-62-211565, the synthesis method by coprecipitation described in JP-A-62-211565, the method of quenching the fired product described in JP-A-5-198301 and JP-A-5-205741, JP-A-5-283076, A method of firing by pellet molding described in JP-A-6-310145, a method of firing in a molten state using LiOH hydrate described in JP-A-5-325969, and synthesis under oxygen partial pressure control described in JP-A-6-60887 Method, a fluorine doping method described in JP-A-6-243871, and active materials having different internal and surface compositions of particles described in JP-A-8-138670. And a method in which it is effective.
[0032]
In the case of Ni oxide or Mn oxide, it is preferable that the positive electrode active material particles have the shape of secondary particles formed by agglomeration of primary particles from the viewpoint of improving cycle life and storage stability. The preferable particle size at this time is such that the particle size of the secondary particles is 1 to 30 μm, the particle size of the primary particles is 0.01 to 1 μm, more preferably the particle size of the secondary particles is 3 to 20 μm, and the primary particles Has a particle size of 0.05 to 0.5 μm. Here, the secondary particle means a particle formed by agglomeration of fine primary particles, and corresponds to a particle size usually measured by a laser scattering particle size distribution measurement or the like, and corresponds to a normally defined particle size.
As for the shape of the particles, the secondary particles are particularly preferably spherical. Moreover, it is preferable that the surface of the secondary particle is porous.
[0033]
The specific surface area of the positive electrode active material corresponds to the above particle form, and is 0.1 to 10 m as measured by the BET method.²  / G is preferred, 0.3-3 m²  / G is more preferable.
[0034]
The positive electrode active material particles used in the present invention may be crystalline or may contain an amorphous structure inside or on the surface, but are preferably crystalline.
[0035]
The conductive agent used in the mixture of the present invention may be anything as long as it is an electron conductive material that does not cause a chemical change in the constructed battery. Specific examples include natural graphite such as scaly graphite, scaly graphite and earthy graphite, high-temperature fired bodies such as petroleum coke, coal coke, celluloses, saccharides and mesophase pitch, and graphite such as artificial graphite such as vapor-grown graphite. , Carbon blacks such as acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc., carbon materials such as asphalt pitch, coal tar, activated carbon, mesofuse pitch, polyacene, conductivity of metal fibers, etc. Examples thereof include fibers, metal powders such as copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium oxide. It is preferable to use a graphite plate having an aspect ratio of 5 or more. Among these, graphite and carbon black are preferable, and the particle size is preferably 0.01 μm or more and 20 μm or less, and more preferably 0.02 μm or more and 10 μm or less. These may be used alone or in combination of two or more. When using together, it is preferable to use together carbon blacks, such as acetylene black, and a 1-15 micrometers graphite particle.
The addition amount of the conductive agent to the mixture layer is preferably 1 to 50% by weight, particularly 2 to 30% by weight, based on the negative electrode material or the positive electrode material. In the case of carbon black or graphite, the content is particularly preferably 3 to 20% by weight.
[0036]
In the present invention, a binder is used to hold the electrode mixture. Examples of the binder include polysaccharides, thermoplastic resins, and polymers having rubber elasticity. Preferred binders include starch, carboxymethyl cellulose, cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium alginate, polyacrylic acid, polyacrylic acid Na, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone. Water-soluble polymers such as polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic acid copolymer, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene furo Ride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene (Meth) acrylic acid ester copolymer containing (meth) acrylic acid ester such as di-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, 2-ethylhexyl acrylate, (meth) acrylic Acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, neoprene rubber, fluoro rubber, polyethylene oxide, polyester polyurethane Resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, phenol resin, epoxy resin emulsion (latex) or suspension It can be cited. In particular, polyacrylate ester latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are exemplified. These binders are more preferably those having an average particle size of 0.01 to 5 μm, and particularly preferably 0.05 to 1 μm.
These binders can be used alone or in combination. When the amount of the binder added is small, the holding power and cohesion of the electrode mixture is weak. If the amount is too large, the electrode volume increases and the capacity per electrode unit volume or unit weight decreases. For this reason, the addition amount of the binder is preferably 1 to 30% by weight, and particularly preferably 2 to 10% by weight.
[0037]
Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable.
As the ionic conductive agent, those known as inorganic and organic solid electrolytes can be used, and details are described in the section of the electrolytic solution.
A pressure enhancer is a compound that increases the internal pressure of a battery, and carbonates such as lithium carbonate are typical examples.
[0038]
In the current collector that can be used in the present invention, the positive electrode is aluminum, stainless steel, nickel, titanium, or an alloy thereof, and the negative electrode is copper, stainless steel, nickel, titanium, or an alloy thereof. The form of the current collector is foil, expanded metal, punching metal, or wire mesh. In particular, an aluminum foil is preferable for the positive electrode and a copper foil is preferable for the negative electrode.
The thickness of the foil is preferably 7 μm to 100 μm, more preferably 7 μm to 50 μm, and particularly preferably 7 μm to 20 μm. The thickness of the expanded metal, punching metal, and wire mesh is preferably 7 μm to 200 μm, more preferably 7 μm to 150 μm, and particularly preferably 7 μm to 100 μm.
The purity of the current collector is preferably 98% or more, more preferably 99% or more, and particularly preferably 99.3% or more.
The surface of the current collector may be washed with an acid, alkali, organic solvent or the like.
[0039]
Next, the configuration of the positive and negative electrodes in the present invention will be described. The positive and negative electrodes are preferably in a form in which an electrode mixture is applied to both sides of the current collector. In this case, the number of layers per side may be one or may be composed of two or more layers. When the number of layers per side is 2 or more, the positive electrode active material (or negative electrode material) -containing layer may be 2 or more. A more preferable configuration is a case where the layer is composed of a layer containing a positive electrode active material (or negative electrode material) and a layer not containing a positive electrode active material (or negative electrode material).
The layer that does not contain the positive electrode active material (or the negative electrode material) includes a protective layer for protecting the layer containing the positive electrode active material (or the negative electrode material) and a divided positive electrode active material (or negative electrode material) containing layer. And an undercoat layer between the positive electrode active material (or negative electrode material) -containing layer and the current collector. These are collectively referred to as an auxiliary layer in the present invention.
[0040]
The protective layer is preferably on both the positive and negative electrodes or on the positive and negative electrodes. In the negative electrode, when lithium is inserted into the negative electrode material in the battery, the negative electrode preferably has a protective layer. The protective layer is composed of at least one layer, and may be composed of a plurality of layers of the same type or different types. Moreover, the form which has a protective layer only in the single side | surface of the mixture layers of both surfaces of a collector may be sufficient. These protective layers are composed of water-insoluble particles and a binder. The binder used when forming the above-mentioned electrode mixture can be used as the binder. As the water-insoluble particles, various kinds of conductive particles and organic and inorganic particles having substantially no conductivity can be used. The solubility of water-insoluble particles in water is 100 PPM or less, preferably insoluble. The ratio of the particles contained in the protective layer is preferably 2.5% by weight or more and 96% by weight or less, more preferably 5% by weight or more and 95% by weight or less, and particularly preferably 10% by weight or more and 93% by weight or less.
[0041]
Examples of water-insoluble conductive particles include carbon particles such as metals, metal oxides, metal fibers, carbon fibers, carbon black, and graphite. Among these water-insoluble conductive particles, those having low reactivity with alkali metals, particularly lithium, are preferable, and metal powders and carbon particles are more preferable. The electrical resistivity at 20 ° C. of the elements constituting the particles is 5 × 10⁹Ω · m or less is preferable.
[0042]
The metal powder is preferably a metal having low reactivity with lithium, that is, a metal that is difficult to form a lithium alloy. Specifically, copper, nickel, iron, chromium, molybdenum, titanium, tungsten, and tantalum are preferable. The shape of these metal powders may be any of acicular, columnar, plate-like, and massive shapes, and the maximum diameter is preferably 0.02 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less. These metal powders are preferably those whose surfaces are not excessively oxidized, and when oxidized, heat treatment is preferably performed in a reducing atmosphere.
[0043]
As the carbon particles, a known carbon material used as a conductive material used in combination when the electrode active material is not conductive can be used. Specifically, a conductive agent used for making an electrode mixture is used.
[0044]
Examples of the water-insoluble particles having substantially no conductivity include fine powder of Teflon, SiC, aluminum nitride, alumina, zirconia, magnesia, mullite, forsterite, and steatite. These particles may be used in combination with conductive particles, and are preferably used in an amount of 0.01 to 10 times that of the conductive particles.
[0045]
The positive (negative) electrode sheet can be prepared by applying a positive (negative) electrode mixture onto a current collector, drying, and compressing.
The mixture is prepared by mixing a positive electrode active material (or negative electrode material) and a conductive agent, adding a binder (suspension or emulsion of resin powder) and a dispersion medium, kneading and mixing, It can be carried out by dispersing with a mixer / disperser such as a mixer, homogenizer, dissolver, planetary mixer, paint shaker or sand mill. As the dispersion medium, water or an organic solvent is used, but water is preferable. In addition, additives such as a filler, an ionic conductive agent, and a pressure enhancer may be added as appropriate. The pH of the dispersion is preferably 5 to 10 for the negative electrode and 7 to 12 for the positive electrode.
[0046]
Application can be performed by various methods, for example, reverse roll method, direct roll method, blade method, knife method, extrusion method, slide method, curtain method, gravure method, bar method, dip method and squeeze method. I can list them. A method using an extrusion die and a method using a slide coater are particularly preferred. The application is preferably performed at a speed of 0.1 to 100 m / min. Under the present circumstances, the surface state of a favorable coating layer can be obtained by selecting the said application | coating method according to the liquid physical property of a mixture paste, and drying property. When the electrode layer is a plurality of layers, it is preferable to apply the plurality of layers at the same time from the viewpoint of uniform electrode production, production cost, and the like. The thickness, length and width of the coating layer are determined by the size of the battery. The thickness of a typical coating layer is 10 to 1000 μm in a compressed state after drying.
The electrode sheet after application is dried and dehydrated by the action of hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air. These methods can be used alone or in combination. The drying temperature is preferably in the range of 80 to 350 ° C, particularly preferably in the range of 100 to 260 ° C. The water content after drying is preferably 2000 ppm or less, and more preferably 500 ppm or less.
For the compression of the electrode sheet, a generally employed pressing method can be used, but a die pressing method and a calendar pressing method are particularly preferable. The press pressure is not particularly limited, but is 10 kg / cm.²  ~ 3t / cm²  Is preferred. The press speed of the calendar press method is preferably 0.1 to 50 m / min. The pressing temperature is preferably room temperature to 200 ° C.
[0047]
The separator that can be used in the present invention is only required to be an insulating thin film having a large ion permeability, a predetermined mechanical strength, and an olefin polymer, a fluorine polymer, a cellulose polymer, polyimide, nylon, Glass fiber and alumina fiber are used, and as a form, a nonwoven fabric, a woven fabric, and a microporous film are used. In particular, the material is preferably polypropylene, polyethylene, a mixture of polypropylene and polyethylene, a mixture of polypropylene and Teflon, or a mixture of polyethylene and Teflon, and the form is preferably a microporous film. In particular, a microporous film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferable. These microporous films may be a single film or a composite film composed of two or more layers having different properties such as the shape, density, and material of the micropores. For example, the composite film which bonded the polyethylene film and the polypropylene film can be mentioned.
[0048]
The electrolytic solution is generally composed of a supporting salt and a solvent. Lithium salt is mainly used as the supporting salt in the lithium secondary battery.
Examples of lithium salts that can be used in the present invention include LiClO.₄, LiBF₄, LiPF₆, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiB₁₀Cl₁₀, LiOSO₂C_nF_{2n + 1}(N is a positive integer of 6 or less), LiN (SO₂C_nF_{2n + 1}) (SO₂C_mF_{2m + 1}) Imide salt (m and n are each a positive integer of 6 or less), LiC (SO₂C_pF_{2p * 1}) (SO₂C_qF_{2q + 1}) (SO₂C_rF_{2r + 1}) (Wherein p, q, and r are positive integers of 6 or less), lower aliphatic lithium carboxylate, LiAlCl₄Li salts such as LiCl, LiBr, LiI, chloroborane lithium and lithium tetraphenylborate can be raised, and these can be used alone or in combination. Above all, LiBF₄And / or LiPF₆What melt | dissolved is preferable.
The concentration of the supporting salt is not particularly limited, but is preferably 0.2 to 3 mol per liter of the electrolytic solution.
[0049]
Solvents that can be used in the present invention include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, trifluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, monofluoromethyl ethylene carbonate, hexafluoromethyl acetate, and methyl trifluoride acetate. , Dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, methyl acetate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 2,2-bis ( Trifluoromethyl) -1,3-dioxolane, formamide, dimethylformamide, dioxolane, dioxane, acetonitrile, nitromethane, ethyl Glyme, phosphoric acid triester, boric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, 3-alkylsydnone (alkyl group is propyl, isopropyl, butyl group, etc.), propylene carbonate derivative And aprotic organic solvents such as tetrahydrofuran derivatives, ethyl ether, and 1,3-propane sultone. These may be used alone or in combination. Among these, carbonate-based solvents are preferable, and it is particularly preferable to use a mixture of a cyclic carbonate and an acyclic carbonate. As the cyclic carbonate, ethylene carbonate and propylene carbonate are preferable. Moreover, as an acyclic carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate are preferable.
As an electrolytic solution that can be used in the present invention, LiCF is added to an electrolytic solution in which ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate or diethyl carbonate is appropriately mixed.₃SO₃LiClO₄, LiBF₄And / or LiPF₆An electrolytic solution containing is preferable. In particular, in a mixed solvent of at least one of propylene carbonate or ethylene carbonate and at least one of dimethyl carbonate or diethyl carbonate, LiCF₃SO₃LiClO₄Or LiBF₄At least one salt selected from the group consisting of LiPF and LiPF₆An electrolytic solution containing is preferable. The amount of the electrolyte added to the battery is not particularly limited, and can be used depending on the amount of the positive electrode material or the negative electrode material or the size of the battery.
[0050]
In addition to the electrolytic solution, the following solid electrolyte can be used in combination.
The solid electrolyte is classified into an inorganic solid electrolyte and an organic solid electrolyte. Well-known inorganic solid electrolytes include Li nitrides, halides, oxyacid salts, and the like. Among them, Li₃N, LiI, Li₅NI₂, Li₃N-LiI-LiOH, Li₄SiO₄, Li₄SiO₄-LiI-LiOH, xLi₃PO₄−_(1-x)Li₄SiO₄, Li₂SiS₃In addition, phosphorus sulfide compounds are effective.
[0051]
In the organic solid electrolyte, a polyethylene oxide derivative or a polymer containing the derivative, a polypropylene oxide derivative or a polymer containing the derivative, a polymer containing an ion dissociation group, a mixture of a polymer containing an ion dissociation group and the above aprotic electrolyte, phosphoric acid A polymer matrix material containing an ester polymer and an aprotic polar solvent is effective. Furthermore, there is a method of adding polyacrylonitrile to the electrolytic solution. A method of using an inorganic and organic solid electrolyte in combination is also known.
[0052]
Further, other compounds may be added to the electrolyte for the purpose of improving discharge and charge / discharge characteristics. For example, pyridine, pyrroline, pyrrole, triphenylamine, phenylcarbazole, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones and N , N′-substituted imidazolidinone, ethylene glycol dialkyl ether, quaternary ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, AlCl₃, Monomers of conductive polymer electrode active materials, triethylenephosphoramide, trialkylphosphine, morpholine, aryl compounds having a carbonyl group, crown ethers such as 12-crown-4, hexamethylphosphoric triamide and 4- Examples thereof include alkylmorpholine, bicyclic tertiary amine, oil, quaternary phosphonium salt, and tertiary sulfonium salt. Particularly preferred is a case where triphenylamine and phenylcarbazole are used alone or in combination.
[0053]
In order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride chloride can be contained in the electrolyte. In addition, carbon dioxide gas can be included in the electrolyte in order to make it suitable for high-temperature storage.
[0054]
The battery assembled as described above is preferably subjected to an aging treatment. The aging treatment includes pre-treatment, activation treatment, post-treatment, and the like, whereby a battery with high charge / discharge capacity and excellent cycleability can be produced. The pretreatment is a treatment for homogenizing the distribution of lithium in the electrode. For example, control of lithium dissolution, temperature control to make the lithium distribution uniform, oscillation and / or rotation treatment, optional charging / discharging A combination is made. The activation process is a process for inserting lithium into the negative electrode of the battery body, and it is preferable to insert 50 to 120% of the amount of lithium inserted during actual use charging of the battery. The post-processing is processing for sufficient activation processing, and includes storage processing for uniform battery reaction and charge / discharge processing for determination, which can be arbitrarily combined.
[0055]
Preferred aging conditions (pretreatment conditions) before activation of the present invention are as follows. The temperature is preferably 30 ° C. or higher and 70 ° C. or lower, more preferably 30 ° C. or higher and 60 ° C. or lower, and further preferably 40 ° C. or higher and 60 ° C. or lower. The open circuit voltage is preferably 2.5 V or more and 3.8 V or less, more preferably 2.5 V or more and 3.5 V or less, and further preferably 2.8 V or more and 3.3 V or less. The aging period is preferably 1 day or more and 20 days or less, and particularly preferably 1 day or more and 15 days or less. The charging voltage for activation is preferably 4.0 V or higher, more preferably 4.05 V or higher and 4.3 V or lower, and still more preferably 4.1 V or higher and 4.2 V or lower.
As an aging condition after activation, the open circuit voltage is preferably 3.9 V or more and 4.3 V or less, particularly preferably 4.0 V or more and 4.2 V or less, and the temperature is preferably 30 ° C. or more and 70 ° C. or less, and 40 ° C. or more and 60 A temperature of not higher than ° C is particularly preferred. The aging period is preferably from 0.2 days to 20 days, particularly preferably from 0.5 days to 5 days.
[0056]
A plurality of the batteries of the present invention are assembled in series and / or in parallel as needed, and stored in a battery pack. In addition to safety elements such as positive temperature coefficient resistors, temperature fuses, fuses and / or current interrupting elements, the battery pack also requires safety circuits (monitoring the voltage, temperature, current, etc. of each battery and / or the entire battery pack) In this case, a circuit having a function of interrupting current may be provided. In addition to the positive and negative terminals of the entire assembled battery, the battery pack should be provided with the positive and negative terminals of each battery, the entire assembled battery, the temperature detection terminal of each battery, the current detection terminal of the entire assembled battery, etc. as external terminals. You can also. The battery pack may incorporate a voltage conversion circuit (such as a DC-DC converter). The connection of each battery may be fixed by welding a lead plate, or may be fixed so that it can be easily attached and detached with a socket or the like. Further, the battery pack may be provided with display functions such as the remaining battery capacity, the presence / absence of charging, and the number of uses.
[0057]
The battery of the present invention is used in various devices. In particular, video movies, portable video decks with built-in monitors, movie cameras with built-in monitors, digital cameras, compact cameras, single-lens reflex cameras, film with lenses, notebook computers, notebook word processors, electronic notebooks, mobile phones, cordless phones, bearded scorpions, It is preferably used for electric tools, electric mixers, automobiles and the like.
[0058]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples unless it exceeds the gist of the invention.
[0059]
Example 1
(Preparation of negative electrode material)
As the negative electrode material, the following various solid compounds mainly composed of silicon were used in the state of mechanically pulverized powder.
Polycrystalline silicon simple substance (compound-1), metallurgically synthesized following alloy compounds: Si-Ag alloy (compound-2 weight ratio 40-60), Si-Al (compound-3 weight ratio 40-60) Si-Ag-Cd (compound-4 weight ratio 40-50-10), Si-Zn (compound-5 weight 40-60), Si-Au (compound-6 weight ratio 20-80), Si-Ag- In (compound-7 weight ratio 40-50-10), Si-Ge (compound-8 weight ratio 40-60), Si-Ag-Sn (compound-9 weight ratio 40-50-10), Si-Ag- Sb (compound-10, weight ratio 40-50-10), metallurgically synthesized Li₄Obtained by mixing silicon eluting Li from Si with isopropyl alcohol in argon gas (compound 11), mixing polycrystalline silicon and colloidal silica fine particles, and heating at 1000 ° C. Si-SiO made from powdered solids in argon gas by a vibration mill₂(Compound-12, weight ratio 90-10), Si-Al obtained by the same method₂O₃(Compound-13 weight ratio 90-10), Ag-plated Si (compound-14 Si-Ag weight ratio 40-60), and Ni-plated silicon as the compound plated on the polycrystalline silicon surface by electroless plating method (Compound-15 Si-Ni weight ratio 20-80), Zn-plated silicon (compound-16 Si-Zn weight ratio 70-30), 3 g of polyvinylidene fluoride dissolved in N-methylpyrrolidone 50 g After adding 30 g of silicon, mixing and kneading, powder (compound-17) dried and pulverized in an automatic mortar was used. Further, compound 11 was coated with Ag by electroless plating (compound-18 Si-Ag weight ratio 65-35), and compound-12 was coated with Ag by electroless plating (compound-19). Si-SiO₂-Ag weight ratio 65-5-30), and a compound (compound-20Si-SiO) coated with polyvinylidene fluoride using the same compound-12.₂-Polyvinylidene fluoride weight ratio 80-10-10).
The average particle size of the powder of the negative electrode material (compounds 1 to 20) was in the range of 0.05 to 4 μm.
Next, 190 g of a powder obtained by sufficiently mixing the above-mentioned silicon material and equal weight of scaly natural graphite, 10 g of polyvinylidene fluoride as a binder were dispersed in 500 ml of N-methyl 2-pyrrolidone, Uniform mixing was performed with a homogenizer to prepare a negative electrode paste.
[0060]
(Preparation of positive electrode active material)
The basic composition is LiNi_0.8Co_0.2O₂  The positive electrode active material (C-1) was synthesized by the following various methods.
LiOH / H as Li raw material₂  O (purity 99.9% or more), Ni (NO) as Ni raw material₃)₂・ 1.5H₂O (purity 99.9% or more), Co (OH) as a Co raw material₂A powder of (purity 99.9% or more) was thoroughly mixed in a mortar under dry air at a molar ratio of 1: 0.8: 0.2, heat-treated at 180 ° C. for 2 hours in an oxygen atmosphere, and then 650 Pre-baking was performed at ° C for 6 hours. The fired product was mixed again, fired at 850 ° C. for 8 hours, and gradually cooled to room temperature at a rate of 1 ° C./minute to synthesize Compound C-1 having the above composition. The obtained particles had a nearly spherical shape, the average primary particle size was 0.1 μm, and the average secondary particle size was 7 μm. The specific surface area by the BET method is 1.7m.²  / G. The peak ratio of (104) plane / (003) plane obtained by X-ray diffraction was 0.6, the a-axis lattice constant was 2.83, and the c-axis lattice constant was 13.89.
Further, active materials having the same basic composition are made of Ni (NO) and Ni raw materials, respectively.₃)₂・ 6H₂The compound C-2 was obtained by synthesis using O (purity 99.9% or higher) and high purity cobalt oxide (purity 99.95% or higher).
These synthetic products were completely dissolved in an aqueous nitric acid solution, and the impurity content of metals other than Li, Co, and Ni was quantified by ICP method. 03 wt%, magnesium (Mg) content of 0.02 wt% or less, strontium (Sr), barium (Ba) content of 0.02 wt% or less, total content of alkaline earth elements Is 0.1% or less, and it has been confirmed that the sulfur content is at a level of 0.1% or less. Moreover, as a result of measuring the moisture content of the active material powder by the Karl Fischer method, it was confirmed that all were at a level of less than 5% by weight.
[0061]
As a comparative experiment, nickel nickel (NiO, etc.) batches that are ranked as low purity (purity 99.5% or less) as Ni raw materials and nickel nitrate, Co raw materials are also ranked as low purity (purity 99.5% or less) The basic composition is LiNi using each batch of cobalt oxide._0.8Co_0.2O₂  A positive electrode active material (compounds C-3 and C-4) was synthesized.
These comparative active materials have an alkaline earth element content or sulfur content at or above 0.1% by weight, as shown in Table 1 below, or active material powder. The water content was more than 0.5%.
[0062]
In addition, LiOH / H as Li raw material₂O, Ni Ni (NO as raw material)₃)₂・ 6H₂Co (NO as a raw material for O and Co)₃)₂・ 6H₂In addition to O, Al (OH) as an Al raw material₃  The active materials (C-5, C-6) having the following compositions were synthesized using manganese nitrate as the Mn raw material, boric acid as the boron raw material, and LiF as the fluorine raw material.
As shown in Table 1 below, the purity of alkaline earth elements and sulfur impurity elements in these active materials is within the scope of the present invention as in the case of C-1 and C-2 described above, and calcium ( It was confirmed that the content of Ca) was 0.05% by weight or less.
LiNi_0.8Co_0.15B_0.05O_2.1(Compound C-5)
LiNi_0.8Co_0.15Al_0.05O_1.9F_0.1(Compound C-6)
[0063]
Further, as a positive electrode active material, lithium manganese cobalt composite oxide Li_1.05Mn_1.95Co_0.05O_4.05(C-7) was synthesized by the following method. Particle size 0.5-30 μm (including primary particles and secondary particles), BET surface area 40-70 m² / G chemically synthesized manganese dioxide (CMD, each containing 1% by weight or less of Mn as an impurity)₂ O_Three And Mn_Three O_Four And less than 0.1% by weight of sulfate, 0.05% by weight or less of Na, K, and Ca, respectively, lithium hydroxide ground to an average particle size of 1 to 10 μm, and cobalt carbonate (purity 99.99). 9%) was mixed at a stoichiometric ratio of the above chemical formula, and the mixture was heat-treated at 600 ° C. for 4 hours, and then calcined in air for 18 hours while changing the temperature conditions in the range of 650 ° C. to 750 ° C. As a result of gradual cooling of the final fired product to room temperature, the obtained particles had an average median diameter of 0.5 μm of primary particles and a particle size of secondary particles of 10 μm as measured by laser particle size distribution measurement. . BET surface area is 2m² / G. As a result of identifying the structure and composition by ICP and X-ray diffraction, the fired product was a spinel crystal type Li_1.05Mn_1.95Co_0.05O_4.05The half-width of the diffraction peak at 2θ = 36 in the X-ray diffraction using Cu-α rays is about 0.3, and the intensity is 27% of the peak at 2θ = 18.6. It was. The lattice constant of the a axis of the crystal was 8.22A. In addition, a small amount of LiMnO is contained in the fired product.₂ It was also found that was mixed. As a result of dispersing 5 g of this fired product in 100 cc of pure water and measuring the pH, it was 8.0. Compound C-7 was completely dissolved in an aqueous nitric acid solution, and the impurity content of metals other than Li, Co, and Mn was quantified by the ICP method. As a result, the content of calcium (Ca) for alkaline earth elements was 0.03 wt. %, Magnesium (Mg) content of 0.02% by weight or less, strontium (Sr), barium (Ba) content of 0.02% by weight or less, and the total content of alkaline earth elements is 0. It was confirmed that the sulfur content was 0.1% or less and the sulfur content was 0.1% or less.
[0064]
200 g of the above various positive electrode active materials and 10 g of acetylene black are mixed with a homogenizer, then 5 g of polyvinylidene fluoride is mixed as a binder, and 500 ml of N-methyl 2-pyrrolidone is added and kneaded and mixed. Created a paste.
The positive electrode mixture paste was applied to both surfaces of a 30 μm thick aluminum foil current collector with a blade coater, dried at 150 ° C., compression-molded with a roller press, and cut into a predetermined size to prepare a belt-like positive electrode sheet. Furthermore, it was sufficiently dehydrated and dried with a far-infrared heater in a dry box (dew point: dry air of −50 ° C. or lower) to prepare a positive electrode sheet. Similarly, a negative electrode mixture paste was applied to a 20 μm copper foil current collector, and a negative electrode sheet was prepared in the same manner as the above positive electrode sheet. The coating amount of the positive and negative electrodes is such that the charge capacity of the first cycle where the positive electrode active material is 4.2 V with respect to lithium metal and the charge capacity of the first cycle where the negative electrode material is 0.0 V match each other. The coating amount of the mixture was adjusted.
[0065]
Next, the electrolytic solution was prepared as follows. In an argon atmosphere, 65.3 g of diethyl carbonate was placed in a 200 cc narrow-necked polypropylene container, and 22.2 g of ethylene carbonate was dissolved little by little while taking care that the liquid temperature did not exceed 30 ° C. Next, 0.4 g of LiBF₄  12.1 g LiPF₆  The solution was dissolved in a small amount in the polypropylene container in order, taking care that the liquid temperature did not exceed 30 ° C. The obtained electrolyte was a colorless and transparent liquid with a specific gravity of 1.135. Moisture was 18 ppm (measured with a trade name MKC-210, Karl Fischer moisture measuring device, manufactured by Kyoto Electronics), free acid content was 24 ppm (measured by neutralization titration with 0.1 N NaOH aqueous solution using bromthymol blue as an indicator) )Met.
[0066]
The cylinder battery was prepared as follows.
A method of making a battery will be described with reference to FIG. The positive electrode sheet prepared above, a separator made of a microporous polyethylene film, a negative electrode sheet and a separator were laminated in this order, and this was wound in a spiral shape. The wound electrode group (2) was housed in a nickel-plated bottomed cylindrical battery can (1) plated with nickel which also serves as a negative electrode terminal, and an upper insulating plate (3) was further inserted. After injecting the electrolyte into the battery can, a laminate of a positive electrode terminal (6), an insulating ring, a PTC element (63), a current interrupter (62), and a pressure sensitive valve element (61) is laminated with a gasket (5 ) To form a cylindrical battery. Batteries 1 to 44 were prepared by combining the positive electrode active material and the negative electrode material as shown in Table 1.
[0067]
The cylindrical battery is charged at 1.5A. In this case, charging was performed at a constant current up to 4.1 V, and the charging current was controlled so as to be kept constant at 4.2 V until 2.5 hours had elapsed from the start of charging. Discharging was carried out at a constant current up to 3.0 V at 0.2 C current. The discharge capacity, average discharge voltage, energy amount (discharge capacity × average discharge voltage) of the first cycle at that time, and the capacity retention rate at the 30th cycle after repeated charge and discharge are shown in Table 1.
[0068]

[0069]
Example 2
A negative electrode mixture paste was prepared in the same manner as described above except that polycrystalline silicon having an average particle diameter of 10 μm was used as a negative electrode material for comparison, and a negative electrode sheet (Comparative Example-1) was prepared. Further, a negative electrode sheet (Comparative Example-2) was prepared in the same manner as described above except that polycrystalline silicon having a particle size of 2 μm was used and the weight ratio of the silicon in the negative electrode mixture was changed to 80:20. A battery 46 was obtained. Furthermore, a negative electrode sheet (Comparative Example-3) was prepared in the same manner as Battery 47 except that mesophase pitch coke was used as the negative electrode material and 2% by weight of acetylene black was added as a conductive auxiliary agent. Using these batteries, tests similar to those of batteries 1 to 44 were performed.
Table 2 shows the results of charge / discharge performance obtained for these comparative batteries.
[0070]

[0071]
When the battery of Example-1 using the compound of the present invention is compared, in the example where the amount of alkaline earth element or sulfur contained as an impurity in the positive electrode active material exceeds the range of the present invention, the cycle life decreases and the performance It is clear that the degradation is accelerated. Moreover, when the battery performance of Example-1 and the battery performance of Comparative Example-1 are compared, it can be seen that the compound having a small average particle size of the negative electrode material is excellent in cycle life. Furthermore, when compared in Example-1, no treatment was performed on the alloy, silicon from which lithium was removed from lithium silicide, silicon to which colloidal silica was adhered, silicon coated with metal by plating, or silicon coated with polyvinylidene fluoride. Cycle life has been improved over silicon without the treatment.
Furthermore, the cycle life is improved by combining the treatment of the present invention in the negative electrode material compared to the single treatment negative electrode material.
Moreover, the battery using the negative electrode material of the present invention from Comparative Example-3 has a higher discharge capacity than that using a carbonaceous material for the negative electrode.
The above results indicate that the positive electrode active material is LiNiO.₂Oxides and LiMn₂O₄LiCoO instead of the base oxide₂And LiCo_1.92Sn_0.08O₂  The same effect was obtained when using.
[0072]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the discharge capacity | capacitance and energy amount can be raised and the non-aqueous secondary battery with improved cycle life can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cylinder battery used in Examples.
[Explanation of symbols]
1 Battery can also serves as negative electrode
2 wound electrode group
3 Upper insulation plate
4 Positive lead
5 Gasket
6 Battery cover that also serves as a positive terminal
61 Pressure sensitive valve
62 Current interrupt device (switch)
63 PTC element

Claims (2)

In a nonaqueous secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a nonaqueous electrolyte, the negative electrode material is a compound containing a silicon atom capable of inserting and releasing lithium, and the positive electrode The active material is Li _x M _1-y D _y O _ba X _a (M is Ni or Co, D is one or more selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, P) X is a halogen element, and is represented by a composition of 0.2 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) Lithium-containing cobalt composite oxide or lithium-containing nickel composite oxide, or Li _x Mn _2-y D _y O _ba X _a (D is one or more elements selected from Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.05 <x ≦ 1.2, 0 ≦ y ≦ 0.5, 3.5 ≦ b ≦ 4.5, 0 ≦ a ≦ 1.0) ones, and the 0.1 wt% content of alkaline earth elements of the positive electrode composite oxide following nonaqueous secondary battery, wherein the content of sulfur of 0.1 wt% or less. The positive electrode active material is Li _x Ni _1-y D _y O _b-a X _a (D is one or more elements selected from Mn, Cr, Fe, Co, Cu, Zn, Mo, Ag, W, B, Al, Ga, In, Sn, Pb, Sb, and P, and X is a halogen element. 0.2 <x ≦ 1.2, 0.1 ≦ y ≦ 0.5, 1.8 ≦ b ≦ 2.3, 0 ≦ a ≦ 1.0) The nonaqueous secondary battery according to claim 1, which is a product.

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