JPWO2013080763A1 - Positive electrode material for lithium ion secondary battery, positive electrode member for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

Composition formula Li2 (M1-yLiy) (Si, MB) O4 (where M is one or more elements selected from the group consisting of Fe, Mn, Co, and Ni. MB is the y component of Li +) Is an element that substitutes for Si to compensate for the electric charge of the above.) And a carbon material, and in the composition formula of the oxide, 0 <y≰0.25, The composite has a sea-island structure in which the oxide is scattered in islands with respect to the carbon material, and the average value of the circle-converted diameters of the islands of the sea-island structure is 3 nm or more and 15 nm or less. Moreover, it is the positive electrode member for lithium ion secondary batteries using the said positive electrode material for lithium ion secondary batteries, and a lithium ion secondary battery.

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode member for a lithium ion secondary battery, and a lithium ion secondary battery.

Lithium ion secondary batteries are widely used as power sources for electronic devices such as mobile phones and notebook personal computers because they are lighter and have a larger capacity than conventional lead secondary batteries and nickel-cadmium secondary batteries. Recently, it has begun to be used as a battery for electric vehicles, plug-in hybrid vehicles, electric motorcycles and the like.
A lithium ion secondary battery basically includes a positive electrode, a negative electrode, an electrolyte, and a separator.
Usually, the negative electrode uses metallic lithium, carbon capable of inserting and removing lithium ions, lithium titanate, and the like. As the electrolyte, a lithium salt and an organic solvent or an ionic liquid (ionic liquid) that can dissolve the lithium salt are used. The separator is placed between the positive electrode and the negative electrode to maintain insulation therebetween, and has pores through which the electrolyte can pass, and a porous organic resin, glass fiber, or the like is used.
The positive electrode basically has an active material in which lithium ions can be desorbed and inserted, a conductive auxiliary agent for securing an electric conduction path (electron conduction path) to the current collector, and a combination of the active material and the conductive auxiliary agent. It is composed of a dressing. Carbon materials such as acetylene black, carbon black, and graphite are used as the conductive assistant. Further, as the active material that is a positive electrode material, lithium and transition metal metal oxides such as LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn ₂ O ₄ are generally used. In addition, LiMPO ₄ and derivatives whose elemental substitution and composition change is based on the lithium phosphate metal salt, Li ₂ MSiO ₄ and derivatives whose elemental substitution and composition change are based on the lithium silicate metal salt basic structure, There are derivatives in which element substitution and composition change are performed using LiMBO ₃ or lithium metal borate as a basic structure. Here, M mainly includes transition metal elements such as Fe, Mn, Ni, and Co that change in valence.

Since such a metal oxide generally has a low electronic conductivity, in the positive electrode using the metal oxide as an active material, the conductive additive is mixed as described above. In addition to mixing the conductive assistant, the surface of the metal oxide active material may be coated with carbon, or carbon particles or carbon fibers may be attached to the surface to further improve the electron conductivity in the positive electrode. (See Patent Documents 1 to 6 and Non-Patent Document 1).
In particular, in the case of metal oxides with extremely poor electronic conductivity, it is not sufficient to simply form a positive electrode in the presence of a conductive additive, and excellent battery characteristics cannot be obtained. Used.
Among the above oxides, lithium iron silicate Li ₂ FeSiO ₄ , manganese manganese silicate Li ₂ MnSiO ₄ , and derivatives in which element substitution and composition change are performed using these as basic structures are included in one composition formula. Since it contains two lithium ions, a high capacity can be expected theoretically (see Patent Documents 7 to 11 and Non-Patent Document 2). In addition, since the electron conductivity is particularly low, not only a conductive additive is mixed in the electrode, but also carbon coating on the oxide particles has been attempted (see Non-Patent Documents 3 to 5).
Furthermore, a positive electrode active material containing a compound represented by Li ₂ MSiO ₄ and M selected from two or more transition metals is also known (Patent Document 12). However, here, as described later, there is no disclosure of a composition that can reduce the internal resistance by expanding the direction of movement of lithium ions in a Li ₂ MSiO ₄ solid, and further, a composite of Li ₂ MSiO ₄ and a carbon material. Neither is it disclosed to form a sea-island structure.

Japanese Patent Laid-Open No. 2003-34534 JP 2006-302671 A JP 2002-75364 A JP 2003-272632 A Japanese Patent Laid-Open No. 2004-234777 JP 2003-59491 A JP 2007-335325 A Special table 2005-519451 gazette JP 2001-266882 A JP 2010-108678 A JP 2009-170401 A JP 2010-257592 A

J. Moskon, R. Dominko, R. Cerc-Korosec, M. Gaberscek, J. Jamnik, J. Power Sources 174, (2007) 638-688. R. Dominko, M. Bele, M. Gaberscek, A. Meden, M. Remskar, J. Jamnik, Electrochem. Commun. 8, (2006) 217-222. Tsuji, Izumi Taniguchi, Proc. Of the 50th Battery Conference, (2009) 111. Tsuji, Izumi Taniguchi, Proceedings of the 51st Battery Conference, (2010) 211. Yi-Xiao Li, Zheng-Liang Gong, Yong Yang, J. Power Sources 174, (2007) 528-532. Akira Kojima, Toshikatsu Kojima, Hiroshi Kouki, Mitsue Okumura, Tetsuo Sakai, Abstracts of the 51st Battery Conference, (2010) 194. Yuichi Uemura, Eiji Kobayashi, Takayuki Doi, Shigeto Okada, Junichi Yamaki, Proceedings of the 50th Battery Conference, (2009) 30.

As described above, lithium iron silicate Li ₂ FeSiO ₄ , lithium manganese silicate Li ₂ MnSiO ₄ , and derivatives in which element substitution and composition change are performed using these as basic structures are theoretically or compositionally high in capacity (330 mAh / g ) Can be expected. Actually, there are only a few examples that an actual capacity of 1 Li or more (165 mAh / g) was obtained, and the actual capacity of 1.5 Li (247 mAh / g) has not yet been achieved. The non-patent document 6 reports an actual capacity of 190 mAh / g, and non-patent document 7 reports an actual capacity of 225 mAh / g.
However, in practice, even if a high actual capacity is obtained, if the internal resistance is high, a high voltage cannot be obtained as a battery, so that a substantial energy density is lowered. In addition, when the internal resistance is high, the heat generation of the battery increases, so that it becomes difficult to design the battery unit in a thermal manner. Conventionally, lithium iron silicate and lithium manganese silicate have high theoretical capacity, so efforts have been made to increase the actual capacity. However, the inventors have not been able to increase the actual capacity, but reduce the internal resistance. Clarified that there is a problem that must be done.
In addition, when charging / discharging is repeated with a large charge amount, there is a problem that the internal resistance increases or the actual capacity decreases. In particular, lithium manganese silicate containing Mn has a significant decrease in actual capacity when charging and discharging are repeated.
The present invention has been made in view of the above problems, and is a positive electrode material for a lithium ion secondary battery containing an oxide having a theoretical capacity of 2 Li or more, in a high practical amount, a low internal resistance, and a high charge. It aims at providing the positive electrode material for lithium ion secondary batteries from which the high stability with respect to the repetition of charging / discharging is obtained, the positive electrode member for lithium ion secondary batteries using the same, and a lithium ion secondary battery.

The present inventors have found that a low internal resistance can be obtained with a new material in which the M site in the composition formula Li ₂ MSiO ₄ such as lithium iron silicate and lithium manganese silicate is substituted with lithium ions.
That is, the gist of the present invention is as follows.
(1) Composition formula Li ₂ (M _1-y Li _y ) (Si, M ^B ) O ₄ (where M is one or more elements selected from the group consisting of Fe, Mn, Co, and Ni) there .M ^B, in order to compensate for the y component of the charge of Li ^+, it the oxide represented by an element which replaces the Si.), a composite of the carbon material, the composition of the oxide In the formula, 0 <y ≦ 0.25, and the composite exhibits a sea-island structure in which the oxide is scattered in an island shape with respect to the carbon material, and an average value of a circle-converted diameter of the island of the sea-island structure is 3 nm. This is a positive electrode material for a lithium ion secondary battery having a thickness of 15 nm or less.
(2) The positive electrode material for a lithium ion secondary battery according to (1), wherein the value of y is a multiple of 0.03125.
(3) the M ^B is a positive electrode material for a lithium ion secondary battery according to (1) or (2) that the P.
(4) The lithium ion according to any one of (1) to (3), wherein the composite is a particle having a size of 1 μm or more and 20 μm or less, and voids exist inside the particle. It is a positive electrode material for secondary batteries.
(5) The positive electrode material for a lithium ion secondary battery according to (4), wherein voids having a size of 200 nm or more and less than the particle size exist inside the particles.
(6) The positive electrode material for a lithium ion secondary battery according to (5), wherein the abundance of the voids is 20% or more and 80% or less as an area ratio in the particle cross section.
(7) A lithium ion secondary battery positive electrode material according to any one of (1) to (6) and a metal foil having a positive electrode layer containing a binder, for a lithium ion secondary battery It is a positive electrode member.
(8) A lithium ion using the positive electrode material for a lithium ion secondary battery according to any one of (1) to (6) or the positive electrode member for a lithium ion secondary battery according to (7) It is a secondary battery.

  According to the present invention, a positive electrode material for a lithium ion secondary battery, a positive electrode member for a lithium ion secondary battery, and a lithium ion secondary battery that have high actual capacity, can reduce internal resistance, and have high stability against repeated charge and discharge. It can be.

It is the schematic diagram which showed the internal structure of the composite_body | complex of this invention, and the TEM image of a fracture | rupture part.

The positive electrode material for a lithium ion secondary battery of the present invention is Li ₂ (M _1-y Li _y ) (Si, M ^B ) O ₄ (where M is a group consisting of Fe, Mn, Co, and Ni). is one or more elements selected .M ^B, in order to compensate for the y component of the charge of Li ^+, and those containing oxides represented by an element which replaces the Si.), the oxide In the composition formula of the product, 0 <y ≦ 0.25. That is, the internal resistance can be reduced by using an oxide in which M in the general composition formula Li ₂ MSiO ₄ such as lithium iron silicate and lithium manganese silicate is partially substituted with Li.

The crystal structure of lithium iron silicate, lithium manganese silicate, etc. is between the MSiO ₄ sheet (layer) and the same sheet (layer) between the M oxygen tetrahedron and Si oxygen tetrahedron. The structure contains lithium ions.
The lithium ions between the layers move in a plane (two-dimensionally) between the layers by charging and discharging. One factor of internal resistance is the difficulty of moving lithium ions within the solid.
In the movement of lithium ions between the layers, the movement range is limited to two dimensions. If lithium ions can move through the MSiO ₄ sheet, lithium ions can move between adjacent layers, and the direction of movement can be expanded (three-dimensionalization) to reduce internal resistance. Therefore, lithium ions to penetrate the MSiO ₄ sheets, by replacing part of MSiO ₄ sheets of M lithium ions. When lithium ions to some MSiO ₄ sheet M is present, while lithium ions between the layers are replaced with lithium ions MSiO ₄ in the sheet (as billiard) it can easily be moved between the layers of the next.
Based on this technical idea, it has been found that the internal resistance can be reduced when the substitution amount y of M is 0 <y ≦ 0.25. Therefore, if y is zero or less, the internal resistance cannot be reduced. On the other hand, if y exceeds 0.25, the amount of M responsible for redox is reduced too much, so that a sufficient discharge capacity cannot be obtained.

  The value of y is more preferably a multiple of 0.03125 within the above range. If it is the multiple, a sublattice is formed and the structure is more stable. Therefore, even if charging / discharging is repeated, it is difficult for the structure to change, and it is difficult to reduce the discharge capacity and increase the internal resistance.

Charge compensation of lithium ions replace M is performed by replacing the Si with M ^B. The M ^B, greater pentavalent than the valence of Si, a 6-valent elements. For example, P, As, S, Se, V, Nb, Ta, Mo, W and the like can be mentioned. The charge compensation is more preferably performed with P. The internal resistance is effectively reduced.

  Further, the present invention is a composite of the oxide and carbon material, wherein the composite exhibits a sea-island structure in which the oxide is scattered in an island shape with respect to the carbon material, The average value of the circle equivalent diameter of the island is 3 nm or more and 15 nm or less.

The composite has a plurality of oxide regions, that is, the composite has a structure in which carbon is a matrix (continuous) and the oxide regions are dispersed (non-continuous). As a result, the movement of electrons from each region, which occurs when lithium ions are inserted / extracted from each region, can pass through the carbon material, so that all the regions act as active materials. Therefore, a higher actual capacity can be realized. Furthermore, if the size of the region is small, the distance in which lithium ions diffuse in the solid becomes small and the actual capacity tends to increase. Since the oxide has a very low electric conductivity, a crystal grain size equal to or less than the distance at which lithium ions can be diffused in the solid following the charge / discharge time in order to obtain a high actual capacity in a realistic charge / discharge time. There is a need.
More specifically, a higher actual capacity can be obtained when the projected area of the oxide region in the composite has a circle-equivalent diameter of 15 nm or less. When the diameter exceeds 15 nm, the diffusion distance of lithium ions in the solid becomes large, and lithium ions cannot be diffused within a realistic charge / discharge time, and as a result, a high actual capacity may not be obtained. On the other hand, the lower limit value of the diameter is a minimum size at which lithium ions can be easily held in the oxide structure. Therefore, when the diameter is less than 3 nm, it may be difficult to hold lithium ions in the oxide structure.

Here, the region which is the oxide of the composite can be observed using a transmission electron microscope. The circle-converted diameter of the projected area can be calculated by observing with a transmission electron microscope and image processing.
Specifically, the circle-converted diameter can be calculated from the average value of the diameters when the transmission electron microscope image is binarized and replaced as a circle area. The circle-converted diameter is a number average value of 20 or more of the diameters. Usually, the number average value of 50 is the diameter in terms of a circle.

In the positive electrode material for a lithium ion secondary battery of the present invention, the carbonaceous content is more preferably 2% by mass or more and 25% by mass or less.
When the carbonaceous content is less than 2% by mass, a sufficient electron conduction path to the current collector may not be ensured, and excellent battery characteristics may not be obtained. On the other hand, if the carbonaceous content exceeds 25% by mass, the ratio of the active material when the electrode is produced decreases, so that a high battery capacity may not be obtained depending on the battery design method and purpose. Therefore, if it is within the above range, excellent battery performance can be easily ensured, and the selection range of battery design can be widened.

  The carbon material in the present invention contains elemental carbon, and the content of graphite skeleton carbon contained in the carbon material in the composite particles is preferably 20 to 70%. When the content of graphite skeleton carbon is less than 20%, the electric conductivity of the carbon material becomes low, and it becomes difficult to obtain a high capacity. On the other hand, when the content of the graphite skeleton carbon exceeds 70%, the hydrophobicity becomes strong and the electrolyte solution does not easily permeate, so that it may be difficult to obtain a high capacity.

More preferably, the composite is a particle having a size of 1 μm or more and 20 μm or less, and voids are present inside the particle as shown in FIG.
By doing so, good coatability can be obtained without reducing the capacity, that is, with a high capacity. When the particle size is large, the positive electrode material is easily dispersed uniformly in the coating slurry, and the fluidity of the slurry is improved, so that coating spots are less likely to occur. Therefore, the shrinkage of the coating film that occurs during the coating process and the drying process is also small and uniform, and the occurrence of cracks is also suppressed. In particular, when the coating amount is increased, the above-described effect is remarkably exhibited. That is, when the particle size is less than 1 μm, the coatability may be deteriorated. On the other hand, if the size of the particles exceeds 20 μm, the surface of the coating film may not be uniform due to irregularities caused by the particles. The particle shape is particularly preferably spherical.

  Here, the size of the spherical particles is a circle-converted diameter of the projected area of the spherical particles that can be observed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Using the TEM image or SEM image, the circle-converted diameter is calculated by the average value of the diameters when the observed spherical particles are replaced as the area of the circle. The circle-converted diameter is a number average value of 20 or more of the diameters. Normally, the number average value of 50 is the diameter in terms of yen. If any one image of TEM or SEM is within the scope of the present invention, the above effect can be obtained.

More preferably, voids having a size of 200 nm or more and less than the particle diameter are present inside the particles.
Due to the presence of the voids inside the particles, a high capacity can be obtained even at a high discharge rate. This is because the electrolyte solution can permeate into the voids and can maintain a sufficient amount, so that Li ⁺ ions can be easily exchanged with the electrolyte solution inside the particles even at a high rate. On the other hand, in the absence of voids, the electrolyte solution cannot penetrate a sufficient amount into the interior of the particle, so Li ⁺ ions must diffuse through the solid to the surface of the particle, effectively inserting and removing Li ⁺ ions at high rates. It may become impossible to separate. That is, a high capacity may not be obtained at a high rate.
Here, the size of the void is a circle-equivalent diameter of the projected area of the void where the cross section of the particle can be observed using SEM.

  The abundance of the voids is more preferably 20% or more and 80% or less in terms of the area ratio in the particle cross section. When the area ratio is 20% or more and 80% or less, if it is less than 20%, a high capacity may not be obtained at a high discharge rate, whereas if it exceeds 80%, a high capacity may be obtained even at a high discharge rate. This is because it may be difficult to increase the content of the active material in the electrode.

  The positive electrode material for a lithium ion secondary battery of the present invention can be a positive electrode layer containing at least a binder, and the positive electrode layer is applied to the surface of a metal foil serving as a current collector to be a positive electrode member for a lithium ion secondary battery It can be made.

The binder (also called a binder or a binder) plays a role of binding an active material or a conductive aid.
The binder according to the present invention is usually used when producing a positive electrode of a lithium ion secondary battery.
Moreover, as a binder, what is chemically and electrochemically stable with respect to the electrolyte of a lithium ion secondary battery and its solvent is preferable. The binder may be either a thermoplastic resin or a thermosetting resin. For example, polyolefins such as polyethylene and polypropylene; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetra Fluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), poly Chlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene Fluorine resins such as a lene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer; styrene butadiene rubber (SBR); Ethylene-acrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer; Ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer; Ethylene-methyl acrylate copolymer or the copolymer Examples thereof include Na ⁺ ion cross-linked product of coalescence; ethylene-methyl methacrylate copolymer or Na ⁺ ion cross-linked product of the copolymer; carboxymethyl cellulose and the like. Moreover, these can also be used together. Among these materials, PVDF and PTFE are particularly preferable.
The binder is usually used at a ratio of about 1 to 20% by mass in the total amount of the positive electrode.

The positive electrode layer of the positive electrode member for a lithium ion secondary battery may further contain a conductive additive.
The conductive auxiliary agent is not particularly limited as long as it is substantially a chemically stable electron conductive material. For example, graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon fibers; Other conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; conductive metal oxides such as titanium oxide; organics such as polyphenylene derivatives These may be used alone, or two or more of them may be used simultaneously. Among these, carbon materials such as acetylene black, ketjen black, and carbon black are particularly preferable.
The conductive aid is usually used at a ratio of about 1 to 25% by mass in the total amount of the positive electrode.

  The positive electrode layer includes at least a positive electrode active material and a binder, and has a structure having a gap through which an electrolyte solution can enter. The positive electrode layer may contain a conductive additive in addition to the positive electrode active material and the binder.

  The metal foil is a conductive metal foil, and for example, a foil made of aluminum or an aluminum alloy can be used. The thickness can be 5 μm to 50 μm.

  A lithium ion secondary battery can be obtained using the lithium ion secondary battery member. For example, in addition to the lithium ion secondary battery member, at least a negative electrode, a separator, and a nonaqueous electrolytic solution are used to form a lithium ion secondary battery.

The negative electrode includes a binder (also referred to as a binder or a binder) as necessary in the negative electrode active material.
The negative electrode active material related to the negative electrode may be any material that can be doped / undoped with metallic lithium or Li ions. Examples of materials that can be doped / undoped with Li ions include graphite, pyrolytic carbons, and cokes. And carbon materials such as glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, and activated carbon. In addition, alloys such as Si, Sn, and In, oxides such as Si, Sn, and Ti that can be charged and discharged at a low potential close to Li, and nitrides of Li and Co such as Li _2.6 Co _0.4 N, etc. A compound can also be used as a negative electrode active material. Furthermore, a part of graphite can be replaced with a metal or oxide that can be alloyed with Li.
When graphite is used as the negative electrode active material, the voltage at the time of full charge can be regarded as about 0.1 V on the basis of Li. Therefore, the potential of the positive electrode is calculated for convenience by adding 0.1 V to the battery voltage. Therefore, it is preferable that the charge potential of the positive electrode is easy to control.

The negative electrode may have a structure having a negative electrode layer containing a negative electrode active material and a binder on the surface of a metal foil serving as a current collector.
As said metal foil, copper, nickel, titanium single-piece | unit or these alloys, or stainless steel foil is mentioned, for example. One of the preferred negative electrode current collector materials used in the present invention is copper or an alloy thereof. Preferred metals that can be alloyed with copper include Zn, Ni, Sn, Al, etc. In addition, Fe, P, Pb, Mn, Ti, Cr, Si, As, and the like may be added in small amounts.

The separator has only to have a large ion permeability, a predetermined mechanical strength, and an insulating thin film. The material is olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon, glass fiber, alumina. Fibers are used, and the form is a non-woven fabric, a woven fabric, or a microporous film.
In particular, the material is preferably polypropylene, polyethylene, a mixture of polypropylene and polyethylene, a mixture of polypropylene and polytetrafluoroethylene (PTFE), or a mixture of polyethylene and polytetrafluoroethylene (PTFE), and the form is a microporous film. Are preferred.
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.

The non-aqueous electrolyte is generally composed of an electrolyte (supporting salt) and a non-aqueous solvent. Lithium salt is mainly used as the supporting salt in the lithium secondary battery.
The lithium salt can be used in the present invention, for example, fluoro represented by _{LiClO 4, LiBF 4, LiPF 6} , LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiOSO 2 C n F 2n + 1 Imide salts represented by sulfonic acid (n is a positive integer of 6 or less), LiN (SO ₂ C _n F _{2n + 1} ) (SO ₂ C _m F _{2m + 1} ) (m and n are each 6 or less positive) ), A metide salt represented by LiC (SO ₂ C _p F _{2p + 1} ) (SO ₂ C _q F _{2q + 1} ) (SO ₂ C _r F _{2r + 1} ) (p, q and r are each 6). The following positive integers), Li aliphatic salts such as lithium lithium carboxylate, LiAlCl ₄ , LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, etc. can be raised, and one or more of these can be mixed Can be used. Among these, a solution in which LiBF ₄ and / or LiPF ₆ is 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.

Non-aqueous solvents include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, trifluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, monofluoromethyl ethylene carbonate, hexafluoromethyl acetate, 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 monoglyme, lithium 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, tetrahydrofuran derivative And aprotic organic solvents such as ethyl ether and 1,3-propane sultone, and ionic liquids. 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. Moreover, an ionic liquid is preferable from the viewpoint of a high potential window and heat resistance.

The electrolyte solution contains LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ and / or LiPF ₆ in an electrolyte solution appropriately mixed with ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate or diethyl carbonate. An electrolyte solution is preferred.
In particular, an electrolysis containing at least one salt selected from LiCF ₃ SO ₃ , LiClO ₄ , and LiBF ₄ and LiPF ₆ in a mixed solvent of at least one of propylene carbonate or ethylene carbonate and at least one of dimethyl carbonate or diethyl carbonate. Liquid is preferred. 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.

In addition to the electrolyte solution, the following solid electrolyte can be used. The solid electrolyte is classified into an inorganic solid electrolyte and an organic solid electrolyte.
Inorganic solid electrolytes include Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, x Li 3 PO 4 - (1-x) Li 4 SiO 4 Li ₂ SiS ₃ , phosphorus sulfide compounds and the like are effective.

  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.

  Moreover, it can be set as a lithium ion secondary battery using the said material for lithium ion secondary batteries, without setting it as the said member for lithium ion secondary batteries. For example, a lithium ion secondary battery is formed by a configuration of a positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution in which a positive electrode layer containing a material for a lithium ion secondary battery, a conductive additive, and a binder is formed on a metal mesh.

The positive electrode material for lithium ion secondary batteries of the present invention can be produced by the following method as an example.
The oxide according to the present invention may be produced by any method such as a dry method or a wet method as long as the oxide can be synthesized. For example, solid phase method (solid phase reaction method), hydrothermal method (hydrothermal synthesis method), coprecipitation method, sol-gel method, gas phase synthesis method (Physical Vapor Deposition: PVD method, Chemical Vapor Deposition: CVD method) , Spray pyrolysis method, flame method, roasting method and the like.

Examples of production by the solid phase method, spray pyrolysis method, and roasting method are shown below.
In addition, in the preparation example of the solid phase method shown below, an organic compound is not added, and a preparation example of a complex of a sea-island structure including an oxide and a carbon material is not described. A composite with a sea-island structure can also be produced.
As a raw material used in the solid phase method, a compound containing an element constituting the oxide, for example, an oxide, a carbonate, an organic acid salt such as acetate or oxalate, or the like is used. The compounds are weighed and mixed according to the composition ratio. For the mixing, a wet mixing method, a dry mixing method, or the like is used. The obtained mixture is fired to synthesize the oxide. The oxide powder obtained by firing is pulverized as necessary. When the unreacted material remains, it may be further baked after pulverization.

As a specific example, in the case of Li ₂ (Mn _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, manganese dioxide, lithium carbonate, silicon dioxide, and ammonium phosphate are weighed so as to have the above chemical composition. And the mixed powder can be produced by firing at a temperature of 700 to 900 ° C. for 5 to 20 hours in a reducing atmosphere.

In the case of Li ₂ (Fe _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, lithium carbonate, iron (II) oxalate dihydrate, silicon dioxide, and ammonium phosphate are added to the chemical composition. It can be produced by weighing and mixing so that the mixed powder is fired at a temperature of 700 to 900 ° C. for 5 to 20 hours in a reducing atmosphere.

  The raw material used in the spray pyrolysis method is a compound containing an element constituting a desired oxide, and a compound that dissolves in water or an organic solvent is used. The solution in which the compound is dissolved is made into droplets by ultrasonic waves, nozzles (one-fluid nozzle, two-fluid nozzle, four-fluid nozzle, etc.), and then the droplet is introduced into a heating furnace at a temperature of 400 to 1200 ° C. The oxide can be produced by thermal decomposition. If necessary, it is further heat-treated or pulverized. Moreover, the oxide containing a carbon material can be produced by including an organic compound in the raw material solution.

As a specific example, in the case of Li ₂ (Mn _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, lithium nitrate, manganese (II) nitrate hexahydrate, colloidal silica, and phosphoric acid are used as the above chemicals. Weigh to make composition and dissolve in water.
Here, if an organic compound is further added to the solution, a sea-island structure can be easily obtained. Examples of the organic compounds include ascorbic acid, monosaccharides (glucose, fructose, galactose, etc.), disaccharides (sucrose, maltose, lactose, etc.), polysaccharides (amylose, cellulose, dextrin, etc.), polyvinyl alcohol, polyethylene glycol, polypropylene glycol, Polyvinyl butyral, polyvinyl pyrrolidone, phenol, hydroquinone, catechol, maleic acid, citric acid, malonic acid, ethylene glycol, triethylene glycol, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, Examples include glycerin.
The addition amount of the organic compound is preferably 0.3 or more in terms of a carbon C / composition formula (for example, Li ₂ (Mn _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ )) contained in the organic compound. If the molar ratio is less than 0.3, the amount of carbon becomes insufficient and an effective sea-island structure may not be formed.
The solution in which the above compound is dissolved can be prepared by, for example, forming droplets with an ultrasonic sprayer, and introducing nitrogen as a carrier gas into a heating furnace at a temperature of 500 to 800 ° C. and thermally decomposing it.

In the case of Li ₂ (Fe _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, lithium nitrate, iron (III) nitrate nonahydrate, tetraethoxysilane, and phosphoric acid have the above chemical composition. Weigh and dissolve in water and add organic compound. Here, tetraethoxysilane is previously dissolved in methoxyethanol, and the solution is dissolved in water. The solution in which the above compound is dissolved can be prepared by, for example, forming droplets with an ultrasonic atomizer and introducing nitrogen as a carrier gas into a heating furnace at a temperature of 500 to 900 ° C. to thermally decompose the solution.

Next, an example of a manufacturing method using a roasting method is shown.
The raw material used in the roasting method is a compound containing an element constituting a desired oxide, and a compound that dissolves in water is used. In the case of an oxide containing an iron element, it is preferable to use a steel pickling waste solution or an aqueous solution prepared by dissolving a rolling scale in hydrochloric acid as the raw material. The oxide can be produced by introducing an aqueous solution in which the compound is dissolved into a Lusner type, Lurgie type, chemilite type or the like roasting furnace and thermally decomposing it. If necessary, it is further heat-treated or pulverized. Moreover, the oxide containing a carbon material can be produced by including an organic compound in the raw material solution.

As a specific example, in the case of Li ₂ (Mn _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, lithium acetate, manganese (II) nitrate hexahydrate, colloidal silica, and phosphoric acid are used as the above chemicals. Weigh to make composition and dissolve in water. It can be prepared by further dissolving glucose in an aqueous solution in which the compound is dissolved, and introducing the solution into, for example, a chemilite-type roasting furnace and thermally decomposing it at a temperature of 500 to 800 ° C. Furthermore, the pulverized particles obtained by wet pulverization with a bead mill may be heat-treated in an inert atmosphere.

Further, in the case of Li ₂ (Fe _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ , for example, lithium carbonate, colloidal silica, aluminum chloride (III) hexahydrate, and phosphoric acid are used in a steel pickling waste solution (for example, , 3.0 mol (Fe) / L concentration hydrochloric acid waste liquid), and the concentration is adjusted to the above chemical composition ratio. Here, an appropriate amount of 18% hydrochloric acid is added in advance to the steel pickling waste solution so as to dissolve all the lithium carbonate. It can be prepared by further dissolving glucose in an aqueous solution in which the compound is dissolved, and introducing the solution into, for example, a Lusner roasting furnace and thermally decomposing it at a temperature of 500 to 800 ° C. Furthermore, the pulverized particles obtained by wet pulverization with a bead mill may be heat-treated in an inert atmosphere.

Examples of the organic compound serving as the carbon source include ascorbic acid, monosaccharides (glucose, fructose, galactose, etc.), disaccharides (sucrose, maltose, lactose, etc.), polysaccharides (amylose, cellulose, dextrin, etc.), polyvinyl Alcohol, polyethylene glycol, polypropylene glycol, polyvinyl butyral, polyvinyl pyrrolidone, phenol, hydroquinone, catechol, maleic acid, citric acid, malonic acid, ethylene glycol, triethylene glycol, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene Examples include glycol dimethyl ether, tripropylene glycol dimethyl ether, and glycerin.
The amount of the organic compound added is preferably 0.3 or more in terms of a carbon C / composition formula (for example, Li ₂ (Fe _0.9375 Li _0.0625 ) (Si _0.9375 P _0.0625 ) O ₄ )) contained in the organic compound. If the molar ratio is less than 0.3, the amount of carbon becomes insufficient and an effective sea-island structure may not be formed.
As a compound containing the element which comprises the above-mentioned metal oxide, a metal, a hydroxide, nitrate, a chloride, an organic acid salt, an oxide, carbonate, a metal alkoxide etc. can be illustrated, for example.

Example 1
Starting materials include lithium nitrate (LiNO ₃ ), manganese (II) nitrate hexahydrate (Mn (NO ₃ ) ₂ · 6H ₂ O), colloidal silica, phosphoric acid (H ₃ PO ₄ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) was used. The raw materials were dissolved in water to prepare an aqueous solution so that the composition ratios in Table 1A were obtained. Furthermore, glucose was added to the aqueous solution as an organic compound to be a carbon material. Samples were prepared by spray pyrolysis of these aqueous solutions, respectively, in a heating furnace heated to 650 ° C. using a carrier gas composed of nitrogen gas. Sample No. 1-11 was sprayed into a 600 ° C. heating furnace. Sample No. 1-14 was sprayed into a heating furnace at 800 ° C.
As shown in Table 1B, Samples No. 1-1 to No. 1-10 were further wet pulverized, and then heat-treated in 1% H ₂ / Ar at 700 ° C. for 5 hours. Sample No. 1-14 was further wet pulverized, and then heat-treated in 1% H ₂ / Ar at 800 ° C. for 2 hours. Samples No. 1-11 to No. 1-12 were neither crushed nor heat-treated. Sample No. 1-13 is obtained by pulverizing Sample No. 1-12 and then granulating it.
The solution was prepared so that the concentration of metal ions in the solution was in the range of 0.33 mol / L in terms of oxide composition mole. The glucose was added in a glucose / oxide molar ratio range of 2.1 or 2.2. Moreover, the sample which is not grind | pulverized is a spherical particle, The size of a spherical particle can be controlled with the metal ion concentration and glucose content in a droplet.
The concentration of metal ions in the solution and the amount of glucose added for each sample are as shown in Table 1A and Table 1B.

<Analysis of each sample>
The following analysis was performed on each sample obtained as described above.
The phase was confirmed using a powder X-ray diffractometer (Ultima II manufactured by Rigaku). Samples No. 1-1 to No. 1-10 and No. 1-14 were heat-treated, and thus had diffraction patterns similar to those of the Li ₂ MnSiO ₄ crystal phase. However, a shift was observed in the diffraction peak in the sample with element substitution. Samples No. 1-11 to No. 1-13 are crystalline with no diffraction peak appearing at 2θ = 15-18 ° in CuKα rays but a broad diffraction peak appearing at 2θ = 33 ± 2 °. It was.
Sample No. 1-1 to Sample No. 1-14 were observed using a transmission electron microscope (H-9000UHR III manufactured by Hitachi). All of these samples were sea-island composites, and the circle-equivalent diameters of the islands (oxides) were calculated by the above-described method, and the circle-equivalent diameters of the obtained samples were also shown in Table 1C.
Using a scanning electron microscope (JSM-7000F, manufactured by JEOL Ltd.), observe the particles of sample No.1-11 to No.1-14, and calculate the circle equivalent diameter as the size of the spherical particles from the image did. The values were as shown in the “Particle Size” column of Table 1C. Since sample No. 1-13 is obtained by pulverizing and granulating sample No. 1-12, it is the size of particles granulated spherically. Although the particles can be observed with a transmission electron microscope, the same particle size was obtained with a transmission electron microscope.
Further, Samples Nos. 1-11 to No. 14 as particles were also observed with a scanning electron microscope. From the image, voids of 200 nm or more in the particles were selected, and the area ratio was determined as the abundance of the voids. Samples No. 1-11 to No. 12 had values as shown in the “area ratio” column of “voids in particles” in Table 1C. Since sample No. 1-13 was a particle obtained by pulverizing and granulating sample No. 1-12, the inside of the particle was dense, and there was no large void such as a 200 nm size.
The content of the carbon material contained in each sample was measured using a carbon / sulfur analyzer EMI-320V manufactured by Horiba, Ltd., and is also shown in Table 1B.

<Evaluation of battery characteristics>
The battery characteristics evaluation of each sample was performed as follows.
First, each sample was mixed with acetylene black powder and polytetrafluoroethylene powder in a mortar at a weight ratio of 70: 25: 5, and then pressed onto a titanium mesh to produce a positive electrode.
A metal lithium foil was used for the negative electrode, and a nickel foil with a thickness of 20 μm was used for the negative electrode current collector.
As the electrolyte, a non-aqueous electrolyte in which 1.0 mol / L LiPF ₆ was dissolved in a 1: 2 mixed solvent of ethyl carbonate and dimethyl carbonate was used, and the separator was porous with a thickness of 25 μm. A CR2032 coin cell was assembled in an argon glove box using polypropylene.
Five coin batteries were prepared for each sample, and a charge / discharge test was performed in a thermostat at 30 ° C. to measure an initial charge / discharge capacity. In the initial charge / discharge test, first, preliminary charge / discharge was repeated once under the CC-CV condition of voltage range 1.0 to 5.0V and 0.1C, then 250mAh / g was charged under the CC-CV condition at 0.1C, and the discharge capacity was determined. The measured result was defined as the initial charge / discharge capacity. In the “Initial charge / discharge capacity” column of Table 1D, the initial charge / discharge capacity of five coin batteries is measured for each sample, and the initial charge / discharge of three coin batteries excluding the maximum and minimum values is measured. The average value of capacity is indicated.
Regarding the effect of reducing the internal resistance, a voltage at 150 mAh / g was obtained from the discharge curve obtained from the initial discharge capacity, and it was determined that the internal resistance was reduced when the voltage increased. The voltage is also obtained from the discharge curve of five coin batteries for each sample, and the average value of the voltages of the three coin batteries excluding the maximum and minimum values is shown in Table 1C.
Furthermore, charge / discharge is repeated up to 10 cycles, and the slope of the voltage change at 150 mAh / g (voltage change per cycle) in the discharge curve between 5 and 10 cycles is obtained, and the stability of the internal resistance reduction effect is obtained. Table 1D lists the values for each sample.
Further, as a discharge capacity maintenance rate, a value of (100 V 2V discharge capacity / 2nd cycle 2V discharge capacity) × 100 is shown in Table 1D.
From the results of Table 1A and Table 1C, sample Nos. 1-2 to No. 1-5 whose y value exceeds zero compared to the voltage at 150 mAh / g of sample No. 1-1 whose y value is zero No. 1-7 to No. 1-8 and No. 1-11 to 1-14 showed an increase in the voltage and an effect of reducing internal resistance. Samples No. 1-6 and No. 1-9 had an y value exceeding 0.25, and thus the internal resistance reduction effect was not observed. Since sample No. 1-10 has a composition formula Li _1.9 Mn (Si _0.9 P _0.1 ) O ₄ different from the composition formula of the present invention, the effect of reducing the internal resistance was not observed. In addition, compared with the voltage at 150 mAh / g of sample No.1-1, No.1-6, No.1-9, No.1-10, the voltage is higher in sample No.1-14. However, the voltage was lower than other samples.
Further, from the results of Table 1A and Table 1D, when the y value is a multiple of 0.03125 and not a multiple of 0.03125, for example, when comparing sample No. 1-2 and No. 1-3, the y value is 0.03125. It is shown that the stability of the effect of reducing the internal resistance is excellent when it is a multiple of.
Moreover, the coating property was evaluated using Sample Nos. 1-11 to 1-13. Each sample is mixed with 90% by mass, 4% by mass of polyvinylidene fluoride (PolyVinylidene DiFluoride, PVDF), and 6% by mass of acetylene black in a dispersion medium (N-methylpyrrolidone, NMP) to prepare a slurry. The slurry was applied onto an aluminum foil having a thickness of 20 μm using a Baker type applicator having a clearance of 300 μm and dried with a dryer at 110 ° C. Visually observe the surface of the coating after drying. If the surface has significant irregularities or cracks occur, the coating properties are poor. If the surface is flat and cracks do not occur, apply the coating properties. It was evaluated as “good”.
Samples No. 1-11 to No. 1-13 had a result of “good coating properties”. Moreover, what has an appropriate space | gap in a spherical particle showed the outstanding discharge capacity even at a high rate.

(Example 2)
Starting materials include lithium nitrate (LiNO ₃ ), iron (III) nitrate nonahydrate (Fe (NO ₃ ) ₃ · 9H ₂ O), tetotraethoxysilane (hereinafter referred to as TEOS), phosphoric acid (H ₃ PO ₄ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) was used. The raw materials were dissolved in water to prepare an aqueous solution so that the composition ratios in Table 2A were obtained. Here, TEOS was dissolved in methoxyethanol in advance, and the solution was dissolved in water. Furthermore, glucose was added to the aqueous solution as an organic compound to be a carbon material.
Samples were prepared by spray pyrolysis of these aqueous solutions, respectively, in a heating furnace heated to 750 ° C. using a carrier gas composed of nitrogen gas. Sample No. 2-18 was sprayed into a heating furnace at 800 ° C.
As shown in Table 2B, Samples No. 2-1 to No. 2-10 were further wet pulverized and then heat-treated in 1% H ₂ / Ar at 550 ° C. for 10 hours. Sample No. 2-18 was further wet pulverized and then heat-treated in 1% H ₂ / Ar at 550 ° C. for 20 hours. Samples No. 2-11 to No. 2-16 were neither crushed nor heat-treated. Sample No. 2-17 is obtained by pulverizing Sample No. 2-12 and then granulating it.
The solution was prepared so that the concentration of metal ions in the solution was in the range of 0.1 to 0.35 mol / L in terms of oxide composition mole. The glucose was added in a glucose / oxide molar ratio range of 2 to 2.4. Moreover, the sample which was not grind | pulverized is a spherical particle, The size of the spherical particle was controlled by the metal ion concentration and glucose content in a droplet.
The concentration of metal ions in the solution and the amount of glucose added for each sample are as shown in Tables 2A and 2B.

<Analysis of each sample>
The samples No. 2-1 to No. 2-18 obtained as described above were analyzed in the same manner as in Example 1.
Samples No. 2-1 to No. 2-18 were measured by X-ray diffraction. Samples No. 2-1 to No. 2-10 and No. 2-18 were heat-treated, so Li ₂ FeSiO The diffraction pattern was similar to that of the _four crystal phases. However, a shift was observed in the diffraction peak in the sample with element substitution. Samples No. 2-11 to No. 2-17 were crystalline with no diffraction peak appearing at 2θ = 15-18 ° with CuKα rays, but having a broad diffraction peak at 2θ = 33 ± 2 °. It was.
From TEM observation, Samples No.2-1 to No.2-18 are all sea-island composites, and the circle-converted diameter of the island (oxide) was calculated by the above-mentioned method, and each sample obtained The circle-converted diameter is also shown in Table 2C.
Using SEM, the spherical particles of Samples No. 2-11 to No. 2-17 were observed, and the circle-converted diameter was calculated as the particle size from the image. The values were as shown in the “Particle Size” column of Table 2C. Samples No. 2-1 to No. 2-9 were pulverized to a size of 0.15 μm, and Sample No. 2-18 were pulverized to a size of 0.18 μm. Of irregularly shaped particles of the size Sample No. 2-17 is the size of particles granulated in a spherical shape because Sample No. 2-12 was pulverized and granulated.
In addition, samples No. 2-11 to No. 2-17, which are spherical particles, were also observed by SEM. From the image, voids of 200 nm or more in the particles were selected, and the area ratio was determined as the abundance of the voids. Samples No. 2-11 to No. 2-16 had values as shown in the “area ratio” column of “voids in particles” in Table 2C. Since sample No. 2-17 was a particle obtained by pulverizing and granulating sample No. 2-12, the inside of the particle was dense and there was no large void such as a 200 nm size.

<Evaluation of battery characteristics>
Regarding the battery characteristic evaluation, only the following points are different from the first embodiment.
In the initial charge / discharge test, first, preliminary charge / discharge was repeated 4 times under the CC-CV condition of voltage range 1.5 to 5.0V and 0.1C, then 250mAh / g was charged under CC-CV condition at 0.1C, and the discharge capacity was The measured result was defined as the initial charge / discharge capacity.
Regarding the effect of reducing the internal resistance, a voltage at 100 mAh / g was obtained from the discharge curve obtained from the initial discharge capacity, and it was determined that the internal resistance was reduced when the voltage increased. Furthermore, charge / discharge is repeated up to 20 cycles, and the slope of voltage change at 100 mAh / g (voltage change per cycle) in the discharge curve between 20 and 25 cycles is obtained, and the stability of the internal resistance reduction effect is did.
Further, the discharge capacity retention rate was set to a value of (1.5 V discharge capacity at the 10th cycle / 1.5 V discharge capacity at the second cycle) × 100.
From the results of Table 2A and Table 2C, sample No. 2-2 to No. 2-5 whose y value exceeds zero compared to the voltage at 100 mAh / g of sample No. 2-1 whose y value is zero No.2-7 to No.2-8 and Nos.2-11 to 2-18 showed an increase in the voltage and an effect of reducing internal resistance. In samples No. 2-6 and No. 2-9, the y value exceeded 0.25, and thus the effect of reducing internal resistance was not observed. Since sample No. 2-10 has a composition formula Li _1.9 Fe (Si _0.9 P _0.1 ) O ₄ different from the composition formula of the present invention, the effect of reducing the internal resistance was not observed.
In addition, compared with the voltage at 100 mAh / g of sample No.2-1, No.2-6, No.2-9, No.2-10, the voltage is higher in sample No.2-18. However, the voltage was lower than other samples.
Further, from the results of Table 2A and Table 2D, when the y value is a multiple of 0.03125 and not a multiple of 0.03125, for example, when comparing sample No. 2-2 and No. 2-3, the y value is 0.03125. It is shown that the stability of the effect of reducing the internal resistance is excellent when it is a multiple of.
Samples No.2-11 to No.2-17 were evaluated for coatability, and No.2-11 to No.2-13 and No.2-15 to No.2-17 The result was “good workability”. Moreover, what the moderate space | gap has in the particle | grains showed the outstanding discharge capacity even at the high rate.

(Comparative example)
Starting materials include lithium carbonate (Li ₂ CO ₃ ), iron (II) oxalate dihydrate (FeC ₂ O ₄ · 2H ₂ O), manganese carbonate (MnCO ₃ ), cobalt oxide (CoO), silicon dioxide ( SiO ₂ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), each oxide listed in the composition column of Table 3A by a solid phase reaction method A powder was prepared.
First, the above raw materials were combined and weighed so that the composition ratio described in the composition column of Table 3A was obtained, and wet-mixed with a ball mill using methanol for 12 hours. Each of the obtained mixtures was baked at 850 ° C. for 24 hours in a nitrogen atmosphere, and then pulverized by a planetary ball mill. Furthermore, the pulverized powder was fired at 950 ° C. for 10 hours in a nitrogen atmosphere to prepare an oxide powder.
Each prepared oxide powder was previously mixed with 10% by mass of acetylene black. As a method for mixing acetylene black, each oxide powder and acetylene black were wet-mixed for 12 hours in a ball mill using ethanol. The resulting mixture was calcined at 400 ° C. for 5 hours under a nitrogen atmosphere.

<Analysis of each sample>
The samples No. 3-1 to No. 3-14 obtained as described above were analyzed in the same manner as in Example 1.
Samples No.3-1 to No.3-10 were X-ray diffracted. Sample Nos.3-1 to No.3-10 had a diffraction pattern similar to the Li ₂ CoSiO ₄ crystal phase as the main phase. Met. Samples Nos. 3-11 to 3-12 had a diffraction pattern similar to that of the Li ₂ FeSiO ₄ crystal phase as the main phase. Samples No. 3-13 to No. 3-14 had a diffraction pattern similar to the Li ₂ MnSiO ₄ crystal phase as the main phase. However, a shift was observed in the diffraction peak in the sample with element substitution.

<Evaluation of battery characteristics>
Regarding the battery characteristic evaluation of Samples No. 3-1 to No. 3-10, only the following points are different from Example 1.
In the initial charge / discharge test, first, preliminary charge / discharge was repeated 4 times under the CC-CV condition of voltage range 1.0-5.0V and 0.1C, then 200mAh / g was charged under CC-CV condition at 0.1C, and the discharge capacity was The measured result was defined as the initial charge / discharge capacity.
Regarding the effect of reducing the internal resistance, a voltage at 100 mAh / g was obtained from the discharge curve obtained from the initial discharge capacity, and it was determined that the internal resistance was reduced when the voltage increased. Furthermore, charge / discharge is repeated up to 20 cycles, the slope of voltage change at 100 mAh / g (voltage change per cycle) in the discharge curve between 15 and 20 cycles is obtained, and the stability of the internal resistance reduction effect is did.
From the results of Table 3A, sample No. 3-2 to No. 3-5, No. 3 with a y value exceeding zero compared to the voltage at 100 mAh / g of sample No. 3-1 with a y value of zero. In 3-7 to No. 3-8, the voltage was increased, and the effect of reducing internal resistance was observed. In samples No. 3-6 and No. 3-9, the y value exceeded 0.25, and thus the effect of reducing internal resistance was not observed. Since Sample No. 3-10 has a composition formula Li _1.9 Co (Si _0.9 P _0.1 ) O ₄ different from the composition formula of the present invention, the effect of reducing the internal resistance was not observed.
Further, from the results of Table 3A and Table 3B, when the y value is a multiple of 0.03125 and when it is not a multiple of 0.03125, for example, when sample No. 3-2 and No. 3-3 are compared, the y value is 0.03125. It is shown that the stability of the effect of reducing the internal resistance is excellent when it is a multiple of.
The battery characteristics evaluation of samples No. 3-11 to No. 3-12 is the same as in Example 2. The battery characteristics evaluation of Samples No. 3-13 to No. 3-14 is the same as in Example 1.
From the results of Table 1C, Table 1D, Table 3A, and Table 3B, Sample No.1-, which is a complex of sea-island structure, compared to Samples No.3-13 to No.3-14, which are not complex of sea-island structure. 4, No.1-7 is excellent in reducing the internal resistance and stability of the internal resistance.
Further, from the results of Table 2C, Table 2D, Table 3A and Table 3B, sample No. 3 which is a complex of sea-island structure is compared with Samples No. 3-11 to No. 3-12 which are not complex of sea-island structure. Nos. 2-4 and No.2-7 are excellent in reducing the internal resistance and stability in reducing the internal resistance.

  The present invention can be used in the field of lithium ion secondary batteries.

Claims (8)

Composition formula Li ₂ (M _1-y Li _y ) (Si, M ^B ) O ₄ (where M is one or more elements selected from the group consisting of Fe, Mn, Co, and Ni). ^B is an element that substitutes Si in order to compensate the charge of Li ⁺ y component)) and a composite of an oxide represented by carbon material,
In the composition formula of the oxide, 0 <y ≦ 0.25,
The composite has a sea-island structure in which the oxide is scattered in an island shape with respect to the carbon material, and an average value of a circle-converted diameter of the island of the sea-island structure is 3 nm or more and 15 nm or less. Positive electrode material for lithium ion secondary battery.   2. The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the value of y is a multiple of 0.03125. Wherein M ^B is a positive electrode material for a lithium ion secondary battery according to claim 1 or 2, characterized in that a P. The composite is a particle having a size of 1 μm or more and 20 μm or less,
The positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein voids are present inside the particles.   5. The positive electrode material for a lithium ion secondary battery according to claim 4, wherein voids having a size of 200 nm or more and less than the particle size exist inside the particles.   6. The positive electrode material for a lithium ion secondary battery according to claim 5, wherein the abundance of the voids is 20% or more and 80% or less as an area ratio in the particle cross section.   A positive electrode member for a lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 6 and a metal foil having a positive electrode layer containing a binder.   A lithium ion secondary battery using the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 6 or the positive electrode member for a lithium ion secondary battery according to claim 7. .

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