WO2013062032A1 - Positive electrode material powder for lithium ion secondary batteries - Google Patents

Abstract

A positive electrode material powder for lithium ion secondary batteries, which contains a crystal represented by general formula: Li_xM_1-yM'_y(XO_z)_n (wherein x, y, z and n respectively satisfy 0 < x ≤ 2, 0 ≤ y < 1, z = 3 or 4, 1 ≤ n ≤ 1.5; M represents at least one transition metal element of the first row of the periodic table; M' represents at least one element selected from among Nb, Ta, Ge, Sn, Al, Ga, Zn, Mg and Cu; and X represents S, P, B or Si). The positive electrode material powder for lithium ion secondary batteries is characterized in that the primary particle diameter (D₁) is 1.8 μm or less and the ratio of the secondary particle diameter (D₂) to the primary particle diameter (D₁), namely D₂/D₁ is 5 or less.

Description

Lithium ion secondary battery positive electrode material powder

The present invention relates to a lithium ion secondary battery positive electrode material powder (hereinafter, also simply referred to as “positive electrode material powder”) used for portable electronic devices, electric vehicles and the like. In particular, the present invention relates to a lithium ion secondary battery positive electrode material powder suitable for a lithium ion secondary battery using a nonflammable electrolyte such as an inorganic solid electrolyte.

Lithium ion secondary batteries have established themselves as high-capacity and lightweight power supplies that are indispensable for portable electronic terminals and electric vehicles. Conventionally, inorganic metal oxides such as lithium cobaltate (LiCoO ₂ ) have been used for the positive electrode material powder of the lithium ion secondary battery. However, with the recent increase in power consumption due to higher performance of electronic devices, further increase in capacity of lithium ion secondary batteries is required. In addition, from the viewpoint of environmental conservation problems and energy problems, there is a demand for switching from materials with a large environmental load, such as cobalt, to more environmentally friendly materials. Furthermore, since the problem of depletion of cobalt resources has attracted attention and the price tends to rise, it is desired to switch to a cheaper cathode material powder.

In recent years, since it is advantageous in terms of cost and resources, among the lithium compounds containing transition metals, the general formula: Li _x M _1-y M ′ _y (XO _z ) _n (x, y, z, n is 0 <x ≦ 2, 0 ≦ y <1, z = 3 or 4, 1 ≦ n ≦ 1.5, M is a transition metal in the first row of the periodic table, and M ′ is Nb, Ta, Ge , Sn, Al, Ga, Zn, Mg, or Cu, and X is S, P, B, or Si) are attracting attention, and various researches and developments are underway ( For example, see Patent Document 1). Li _x M _1-y M ′ _y (XO _z ) _n is superior in stability to LiCoO ₂ and is expected to operate safely at high temperatures. Moreover, since it is a structure having a polyanion such as a phosphate ion as a skeleton, it has a feature of being excellent in resistance to structural deterioration due to a charge / discharge reaction.

By the way, a flammable organic solvent is used for the electrolyte of the lithium ion secondary battery, and there is a risk of ignition. In order to fundamentally solve this problem, incombustible electrolytes have been proposed in place of combustible organic solvent electrolytes in recent years.

A typical example of a nonflammable electrolyte is a lithium ion conductive solid electrolyte which is an inorganic substance. When an inorganic solid electrolyte is used, not only can safety be improved, but the battery can be thinned and integrated with an electronic circuit. Furthermore, since the inorganic solid electrolyte has ion selectivity, the cycle life and the storage life can be improved, and the reliability of the battery can be improved. Until now, it has been reported that good battery characteristics can be obtained in an all-solid-state lithium ion secondary battery using LiCoO ₂ as a positive electrode material powder (see, for example, Non-Patent Document 1).

Incidentally, the relationship between the ion selectivity of the electrolyte and the battery characteristics is explained as follows.

In lithium ion secondary batteries using liquid electrolytes, many of the causes of capacity reduction and self-discharge associated with charge / discharge cycles are due to side reactions occurring in the battery. Specifically, in the liquid electrolyte, in addition to the lithium ions that contribute to the electrode reaction of the lithium ion secondary battery, anions, solvent molecules, impurities, and the like also move. When these substances diffuse to the surface of the positive electrode having a high oxidizing power or the negative electrode having a high reducing power, they are oxidized or reduced. Such a side reaction may cause deterioration of battery characteristics.

Since the liquid electrolyte has no ion selectivity, the above side reaction is likely to occur in a battery using the liquid electrolyte. On the other hand, the inorganic solid electrolyte has ion selectivity. That is, only lithium ions move through the lithium ion conductive inorganic solid electrolyte. Therefore, unlike the liquid electrolyte, a substance other than lithium ions hardly causes a side reaction on the electrode surface. Therefore, a lithium ion secondary battery (all solid lithium ion secondary battery) using an inorganic solid electrolyte has characteristics of long life and low self-discharge.

JP-A-9-134725

As described above, the all-solid-state lithium ion secondary battery using Li _x M _1-y M ′ _y (XO _z ) _n is the environmental and resource cost in response to future demand for lithium ion secondary batteries. Li _x M _1-y M ′ _y (XO _z ) _n is superior to the original performance (theoretical value) in terms of energy density and power density when combined with a solid electrolyte. There is a problem that it is extremely low. Therefore, at present, no all-solid-state lithium ion secondary battery using Li _x M _1-y M ′ _y (XO _z ) _n and having good output characteristics has been obtained so far.

In view of the above problems, the present invention is superior in terms of environmental aspects and resource costs, and is capable of achieving good output characteristics even in combination with a solid electrolyte. The purpose is to provide.

The present invention has the general formula: Li _x M _1-y M ′ _y (XO _z ) _n (x, y, z, n are 0 <x ≦ 2, 0 ≦ y <1, z = 3 or 4, 1 ≦ n ≦ 1.5, M is at least one transition metal in the first row of the periodic table, M ′ is at least one of Nb, Ta, Ge, Sn, Al, Ga, Zn, Mg, or Cu , X is S, a lithium ion secondary battery positive electrode material powder containing crystal represented by P, a B or Si), a primary particle diameter D ₁ is less than or equal to 1.8 .mu.m, and the primary particle The present invention relates to a positive electrode material powder for a lithium ion secondary battery, wherein the ratio D ₂ / D _{1 of the} diameter D ₁ and the secondary particle diameter D ₂ is 5 or less.

In general, it is known that the positive electrode material powder is more advantageous for battery reaction as its primary particle size is smaller. However, according to the investigation by the present inventors, in the Li _x M _1-y M ′ _y (XO _z ) _n- based positive electrode material powder, an aggregate of primary particles tends to be formed simply by making the primary particles fine. It became clear that the battery output characteristics deteriorated because the mixed state with the solid electrolyte became inhomogeneous. For this reason, in order to obtain an all solid state battery having excellent output characteristics using Li _x M _1-y M ′ _y (XO _z ) _n- based positive electrode material powder, not only the primary particle diameter D ₁ but also the primary particle diameter D ratio _D 2 / _{D 1} of ₁ relative to the secondary particle diameter _{D 2} can also be controlled is an important requirement.

Specifically, by the first _{Li x M 1-y M '} y (XO z) primary particle diameter _{D 1} of the positive electrode material powder containing _n crystals below 1.8 .mu.m, the specific surface area of the positive electrode material powder Since it becomes large, it is possible to increase the number of sites that release and occlude lithium ions. Furthermore, the ratio D _{2 /} D ₁ of the secondary particle diameter D ₂ to the primary particle diameter D ₁ by regulating the 5 below, in the case of preparing a positive electrode mix powder is mixed with the positive electrode material powder and solid electrolyte powder The solid electrolyte powder can be uniformly dispersed and adhered to the surface of the positive electrode material powder. Thereby, since the ion conductivity in the all-solid-state lithium ion secondary battery can be significantly improved (increase in internal resistance can be suppressed), it is possible to improve the discharge capacity.

When a liquid electrolyte is used, even if D ₂ / D ₁ is large to some extent, the liquid electrolyte penetrates into the voids of the secondary particles, and a sufficient contact area with the positive electrode material powder is ensured. Therefore, the ion conductivity is not significantly affected. Therefore, it can be said that the positive electrode material particles of the present invention are particularly effective when used in combination with a solid electrolyte.

In the present invention, the primary particle diameter D ₁ refers to the value calculated from the electron microscopic observation image. Specifically, 20 positive electrode material powder particles are randomly selected from an electron microscope image and calculated from an average value of their particle diameters. In addition, about flat particle | grains, let the average value of a long diameter and a short diameter be a particle diameter. On the other hand, the secondary particle diameter D ₂ refers measured D ₅₀ value using a laser diffraction scattering method (average particle diameter on a volume basis).

Second, in the lithium ion secondary battery positive electrode material powder of the present invention, M is preferably Fe or Mn or a mixture thereof.

According to this configuration, the positive electrode material powder can be manufactured at low cost.

Third, in the lithium ion secondary battery positive electrode material powder of the present invention, X is preferably P.

According to this configuration, since the ion conductivity in the positive electrode material powder is high, the internal resistance of the all-solid-state lithium ion secondary battery is small, and it is possible to achieve a good discharge capacity.

Fourthly, the present invention relates to a lithium ion secondary battery positive electrode mixture powder comprising any one of the above lithium ion secondary battery positive electrode material powder particles and a solid electrolyte powder.

Fifth, in the lithium ion secondary battery positive electrode mixture powder of the present invention, the solid electrolyte powder is preferably composed of a sulfide-based solid electrolyte powder.

According to this configuration, since the electric conductivity of the solid electrolyte powder is increased, the internal resistance of the all-solid-state lithium ion secondary battery is reduced, and a better discharge capacity can be achieved.

Sixth, the present invention relates to a lithium ion secondary battery comprising: a positive electrode containing any one of the above lithium ion secondary battery positive electrode mixture powder; and an electrolyte layer containing a solid electrolyte powder.

According to the present invention, there is provided a positive electrode material powder for a lithium ion secondary battery that is excellent in terms of environmental aspects and resource costs, and can achieve good output characteristics even in combination with a solid electrolyte. It becomes possible.

It is a graph which shows the relationship between the discharge potential at the time of performing a charging / discharging test in Example 1, and discharge capacity. It is a graph which shows the relationship between the discharge potential at the time of performing a charging / discharging test in the comparative example 1, and discharge capacity. It is a graph which shows the relationship between the discharge potential at the time of performing a charging / discharging test in the comparative example 2, and discharge capacity.

The lithium ion secondary battery positive electrode material powder of the present invention is a lithium ion secondary battery positive electrode material powder containing crystals represented by the general formula: Li _x M _1-y M ′ _y (XO _z ) _n , The particle diameter D ₁ is 1.8 μm or less, and the ratio D ₂ / D ₁ between the primary particle diameter D ₁ and the secondary particle diameter D ₂ is 5 or less.

The primary particle diameter _{D 1} of the positive electrode material powder is 1.8μm or less, 1.6 [mu] m or less, more preferably 1.4μm or less. When the primary particle diameter D ₁ is too large, with a lithium ion it is hardly diffused smaller the specific surface area of the positive electrode material powder, the internal resistance increases, the discharge capacity tends to decrease. On the other hand, the lower limit is not particularly limited, but if it is too small, the cohesive force between the positive electrode material powder particles becomes strong, so that D ₂ / D ₁ tends to increase. As a result, the internal resistance of the electrode increases and the discharge capacity tends to decrease. Therefore, it is preferable primary particle diameter _{D 1} of the positive electrode material powder is 0.05μm or more, especially 0.1μm or more.

The ratio D _{2 /} D ₁ of the primary particle diameter D ₁ of the positive electrode material powder and the secondary particle diameter D ₂ is 5 or less, 4 or less, and particularly preferably 3 or less. If D ₂ / D ₁ is too large, the solid electrolyte powder is difficult to disperse and adhere to the gaps between the positive electrode material powders, and the lithium ion diffusion path is cut off, so the discharge capacity of the all-solid lithium ion secondary battery decreases. Tend to.

M in the Li _x M _1-y M ′ _y (XO _z ) _n crystal is a transition metal in the first row of the periodic table, and is preferably Fe or Mn, particularly Fe, from the viewpoint of raw material costs. It is preferable. M may be a mixture of two or more elements.

M ′ is Nb, Ta, Ge, Sn, Al, Ga, Zn, Mg, or Cu, and may be a mixture of these elements.

X is S, P, B or Si, particularly preferably P. When X is P, the ionic conductivity in the positive electrode material powder is increased, the internal resistance of the all-solid lithium ion secondary battery is small, and a good discharge capacity can be achieved.

X, y, z, and n are 0 <x ≦ 2, 0 ≦ y <1, z = 3 or 4, and 1 ≦ n ≦ 1.5, respectively. Z is 3 when X is B, and 4 when X is S, P or Si.

The specific surface area of the positive electrode material powder of the lithium ion secondary battery of the present invention is preferably 5 m ² / g or more, 15 m ² / g or more, particularly preferably 25 m ² / g or more. When the specific surface area of the positive electrode material powder satisfies the above range, the contact area between the positive electrode material powder and the solid electrolyte powder is increased, lithium ion and electron can be easily transferred, and the discharge capacity can be improved. On the other hand, the upper limit is not particularly limited, but if it is too large, moisture tends to be adsorbed on the surface of the positive electrode material powder, which may cause a decrease in battery performance during charging and discharging. Therefore, the specific surface area of the positive electrode material powder is preferably 100 m ² / g or less, 80 m ² / g or less, and particularly preferably 60 m ² / g or less.

In the positive electrode material powder, the content of Li _x M _1-y M ′ _y (XO _z ) _n crystal is preferably 20% by mass or more, 50% by mass or more, and particularly preferably 70% by mass or more. When the content of _{Li x M 1-y M '} y (XO z) n crystals is too small, there tends to be inferior in discharge capacity. In addition, although it does not specifically limit about an upper limit, In reality, it is 99 mass% or less, Furthermore, it is 95 mass% or less.

As the crystallite size of the Li _x M _1-y M ′ _y (XO _z ) _n crystal is smaller, the particle diameter of the positive electrode material powder can be reduced, and the electrical conductivity can be improved. Specifically, the crystallite size is preferably 100 nm or less, particularly preferably 80 nm or less. The lower limit is not particularly limited, but is actually 1 nm or more, and further 10 nm or more. The crystallite size is determined according to Scherrer's formula from the analysis result of powder X-ray diffraction.

The lithium ion secondary battery positive electrode material powder of the present invention preferably has a tap density of 0.3 g / ml or more, particularly 0.5 g / ml or more. As a result, the contact area between the positive electrode material powder and the solid electrolyte powder is increased, and the fluidity of the positive electrode material powder particles is increased. Therefore, when the positive electrode material powder is mixed with the positive electrode material powder and the solid electrolyte powder, the porosity is reduced. Can be lowered. The upper limit is approximately a value corresponding to the true specific gravity, but in consideration of the agglomeration of the powder, it is practically 5 g / ml or less, particularly 4 g / ml or less.

In the present invention, the tap density is a value measured under tapping conditions of tapping stroke: 10 mm, tapping frequency: 250 times, tapping speed: 2 times / second.

The positive electrode material powder containing Li _x M _1-y M ′ _y (XO _z ) _n crystal is prepared by preparing a raw material powder, and using the obtained raw material powder, a solid phase reaction process, a hydrothermal synthesis process, a melting process, It can be obtained by a sol-gel process, a chemical vapor synthesis process such as spraying a solution mist into a flame, a mechanochemical process, or the like. In particular, a positive electrode material powder containing Li _x M _1-y M ′ _y (XO _z ) _n crystal obtained by a melting process is preferable because it has excellent high-speed charge / discharge performance.

Specifically, the positive electrode material powder is produced by a method including (1) a step of melting and vitrifying the raw material powder, and (2) a step of pulverizing the molten glass after molding. According to this method, it is possible to produce a homogeneous positive electrode material powder containing Li _x M _1-y M ′ _y (XO _z ) _n crystal at low cost.

In step (1), the melting temperature may be appropriately adjusted so that the raw material powder is uniformly melted. Specifically, it is preferably 900 ° C. or higher, particularly 1000 ° C. or higher. Although an upper limit is not specifically limited, Since it will lead to an energy loss when too high, it is preferable that it is 1500 degrees C or less, especially 1400 degrees C or less.

In the step (2), the method for forming molten glass is not particularly limited. For example, the molten glass may be poured between a pair of cooling rolls and formed into a film shape while rapidly cooling, or the molten glass may be poured out into a mold and formed into an ingot shape.

Further, the method for pulverizing the molded body in the step (2) is not particularly limited, and a general pulverizing apparatus such as a ball mill or a bead mill can be used. In addition, you may perform simultaneously the process of grind | pulverizing a molded object, and the process of mixing carbon, surfactant, etc. which are mentioned later. In this way, the number of processes can be reduced and the cost can be reduced.

In a Li _x M _1-y M ′ _y (XO _z ) _n crystal, when M is composed of Fe element and X is composed of P element, the positive electrode material powder has a composition of mol%, Li ₂ O 20-50%, Fe ₂ O ₃ 5 _{~ 40%,} is preferably a crystalline or crystallized glass containing P 2 O 5 20 ~ 50% . The reason for limiting the composition in this way will be described below.

Li ₂ O is a main component of Li _x Fe _1-y M ′ _y PO ₄ crystal. The Li ₂ O content is preferably 20 to 50%, particularly preferably 25 to 45%. When the content of Li ₂ O is too small or too large, Li _x Fe _1-y M ′ _y PO ₄ crystals are difficult to precipitate.

Fe ₂ O _{3 is} also a main component of Li _x Fe _1-y M ′ _y PO ₄ crystal. The content of Fe ₂ O ₃ is preferably 5 to 40%, 15 to 35%, 25 to 35%, particularly 31.6 to 34%. If the content of Fe ₂ O ₃ is too small, Li _x Fe _1-y M ′ _y PO ₄ crystals are difficult to precipitate. On the other hand, if the content of Fe ₂ O ₃ is too large, Li _x Fe _1-y M ′ _y PO ₄ crystals are difficult to precipitate and undesired Fe ₂ O ₃ crystals are likely to precipitate.

P ₂ O _{5 is} also a main component of Li _x Fe _1-y M ′ _y PO ₄ crystal. The content of P ₂ O ₅ is preferably 20 to 50%, particularly preferably 25 to 45%. When the content of P ₂ O ₅ is too small or too large, Li _x Fe _1-y M ′ _y PO ₄ crystals are difficult to precipitate.

In addition to the above components, examples of components that improve glass forming ability include Nb ₂ O ₅ , V ₂ O ₅ , SiO ₂ , B ₂ O ₃ , GeO ₂ , Al ₂ O ₃ , Ga ₂ O ₃ , and Sb ₂ O. ₃ or Bi ₂ O ₃ may be added. The total amount of these components is preferably 0 to 25%, particularly preferably 0.1 to 25%. If the total amount of the above components is too small, it is difficult to obtain the above effect, and if it is too large, the amount of Li _x Fe _1-y M ′ _y PO ₄ crystals precipitated tends to decrease.

Among these, Nb ₂ O ₅ is an effective component for obtaining a homogeneous glass. The content of Nb ₂ O ₅ is preferably 0.05 to 10%, 0.1 to 5%, particularly preferably 0.2 to 3%. If the content of Nb ₂ O ₅ is too small, it is difficult to obtain a homogeneous glass. On the other hand, when the content of Nb ₂ O ₅ is too large, the heterogeneous crystals such niobate iron upon crystallization is deposited, charge-discharge characteristics tend to deteriorate.

The lithium ion secondary battery positive electrode material powder of the present invention is preferably coated on the surface with a coating layer containing carbon (hereinafter also referred to as “carbon-containing layer”). By covering with the carbon-containing layer, the electron conductivity can be increased and the discharge capacity can be improved.

In this case, the proportion of the carbon-containing layer in the positive electrode material powder is preferably 0.01 to 10% by mass, 0.1 to 8% by mass, and particularly preferably 0.5 to 5% by mass. If the proportion of the carbon-containing layer is too small, the formation of the carbon-containing layer tends to be insufficient. On the other hand, when the proportion of the carbon-containing layer is too large, the content of Li _x M _1-y M ′ _y (XO _z ) _n crystal functioning as the positive electrode active material becomes relatively small, and the amount per unit mass of the positive electrode material powder The discharge capacity tends to be small.

As a method of coating the surface of the positive electrode material powder with the carbon-containing layer, it is preferable to add carbon or an organic compound to the positive electrode material powder and perform heat treatment in an inert or reducing atmosphere. Carbon and an organic compound remain as a carbonaceous film on the surface of the positive electrode active material particles containing Li _x M _1-y M ′ _y (XO _z ) _n crystal even after heat treatment, and serve as a conductive active material for imparting conductivity. Also has a role.

Examples of carbon include graphite, acetylene black, and amorphous carbon. As the amorphous carbon, those in which a CO bond peak and a CH bond peak causing a decrease in conductivity of the positive electrode material powder are not substantially detected in the FTIR analysis are preferable. Examples of the organic compound include surfactants, carboxylic acids such as aliphatic carboxylic acids and aromatic carboxylic acids, glucose, and organic binders.

As the surfactant, any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant and a nonionic surfactant may be used, and in particular, a nonionic having excellent adsorptivity to the surface of the inorganic powder. A surfactant is preferred.

Nonionic surfactants include polyoxyalkylene alkyl phenyl ether, polyoxyalkylene alkyl ether, alkyl glucoside, polyoxyalkylene alkyl glucoside, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyalkylene fatty acid ester, polyoxyalkylene fatty acid Ether, polyoxyalkylene allyl ether, polyoxyalkylene sorbitan fatty acid ester, polyoxyethylene polyoxypropylene ether, polyoxyethylene polyoxypropylene glycol, polyoxyalkylene block copolymer, fatty acid alkanolamide, glycerin fatty acid ester, propylene glycol fatty acid Examples thereof include esters and fatty alcohol ethoxylates. Among these, nonionics having a polyoxyalkylene chain, such as polyoxyalkylene alkyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyalkylene fatty acid ester, polyoxyalkylene sorbitan fatty acid ester, etc., which are particularly excellent in adsorptivity to the surface of inorganic powder. It is preferable that it is an ionic surfactant.

The mass average molecular weight of the surfactant is preferably 100 to 10,000, 200 to 5,000, particularly 300 to 3,000. If the mass average molecular weight of the surfactant is too small, the van der Waals force becomes small and the adsorption force of the surfactant to the surface of the positive electrode material powder becomes small, so that the thickness of the carbon-containing layer tends to be uneven. On the other hand, if the mass average molecular weight of the surfactant is too large, the steric hindrance of the molecules will increase, making it difficult to adsorb on the surface of the positive electrode material powder, making it difficult to form a carbon-containing layer.

The addition amount of the surfactant is preferably 0.01 to 50 parts by weight, 0.1 to 50 parts by weight, 1 to 30 parts by weight, particularly 5 to 20 parts by weight with respect to 100 parts by weight of the positive electrode material powder. . If the addition amount of the surfactant is too small, the formation of the carbon-containing layer tends to be insufficient. On the other hand, when the addition amount of the surfactant is too large, the thickness of the carbon-containing layer is increased, the movement of lithium ions is hindered, and the discharge capacity tends to decrease. In addition, in a lithium ion secondary battery, the potential difference between the positive electrode and the negative electrode is reduced, and a desired electromotive force may not be obtained.

The solid electrolyte powder is not particularly limited, and those known in this technical field can be used, but it is preferable to use a sulfide-based solid electrolyte powder. Thereby, since the electrical conductivity of the solid electrolyte powder is increased, the internal resistance of the all-solid-state lithium ion secondary battery is reduced, and it is possible to achieve a better discharge capacity.

Examples of the sulfide-based solid electrolyte powder include glass powder and crystallized glass powder composed of sulfur atoms (S), phosphorus atoms (P), and lithium atoms (Li). The glass powder or crystallized glass powder may contain other atoms such as Al, B, Si, and Ge.

As a raw material of the solid electrolyte powder, lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ); or lithium sulfide, simple phosphorus and simple sulfur; and further, lithium sulfide, diphosphorus pentasulfide, simple substance A combination of phosphorus and / or elemental sulfur may be used. In addition, P ₂ S ₃ , SiS ₂ , B ₂ S ₃ , GeS ₂ , Al ₂ S ₃ , P ₂ O ₅ , Li ₃ PO ₄ , Li ₄ SiO ₄ , LiI, etc. may be used as the raw material. . Moreover, you may use the material which consists of an organic compound and both organic and inorganic compounds.

Regarding the blending of the raw materials, for example, when lithium sulfide and diphosphorus pentasulfide are mixed, the molar ratio is usually Li ₂ S: P ₂ S ₅ = 50: 50 to 87.5: 12.5, preferably Li ₂ S. : P ₂ S ₅ = 60: 40 to 80:20, particularly preferably Li ₂ S: P ₂ S ₅ = 70: 30 to 80:20.

A glassy solid electrolyte is obtained by a method in which the raw material is melt-reacted and then rapidly cooled, a method in which the raw material is processed by a mechanical milling method (MM method), or the like. Further, a crystallized solid electrolyte is obtained by heat treatment. From the viewpoint of ion conductivity, a crystallized solid electrolyte is preferable.

The average particle diameter (D ₅₀ ) of the solid electrolyte powder is preferably 0.01 to 50 μm, 0.1 to 10 μm, particularly preferably 0.1 to 7 μm. If the average particle size of the solid electrolyte powder is too small, secondary aggregation is likely to occur, and ion conductivity may be reduced. Moreover, it becomes difficult to mix with positive electrode material powder uniformly. On the other hand, if the average particle size of the solid electrolyte powder is too large, the ion conductivity may be reduced.

In the positive electrode mixture powder of the present invention, the mixing ratio of the positive electrode active material particles and the solid electrolyte powder is appropriately adjusted in consideration of charge / discharge capacity and ion conductivity. Specifically, the mixing ratio (mass ratio) of the positive electrode active material particles and the solid electrolyte powder is preferably 95: 5 to 30:70, particularly 90:10 to 40:60.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to these examples.

Example 1
(1) Preparation of inorganic powder Using lithium metaphosphate (LiPO ₃ ), lithium carbonate (Li ₂ CO ₃ ), ferric oxide (Fe ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ) as raw materials, , Li ₂ O 35.1%, Fe ₂ O ₃ 32.2%, P ₂ O ₅ 32.2%, Nb ₂ O ₅ 0.5% composition of raw material powder, For 1 hour in the air atmosphere. Thereafter, molten glass was poured into a pair of rolls and formed into a film shape while rapidly cooling to produce crystalline glass. Here, “crystalline glass” refers to glass having the property of precipitating crystals by heat treatment.

The obtained crystalline glass was crystallized by heat treatment at 800 ° C. for 30 minutes, followed by ball milling using Al ₂ O ₃ cobblestone of φ20 mm for 5 hours, and then in alcohol using ZrO ₂ boulder of φ5 mm. Was milled for 40 hours, and bead milling for 8 hours in alcohol using ZrO ₂ beads having a diameter of 0.3 mm to obtain a crystallized glass powder having an average particle size (D ₅₀ ) of 0.5 μm.

(2) Preparation of lithium ion secondary battery positive electrode material powder Polyethylene oxide nonylphenyl ether (HLB value: 13.3 mass average molecular weight) which is a nonionic surfactant as a carbon source with respect to 100 mass parts of crystallized glass powder. : 660) 11.8 parts by mass (corresponding to 7 parts by mass in terms of graphite) and 60 parts by mass of pure water were sufficiently mixed and then dried at 100 ° C. for about 1 hour. Thereafter, a heat treatment was performed at 800 ° C. for 30 minutes to obtain a positive electrode material powder having a carbon-containing layer formed on the surface of the crystallized glass powder. When the positive electrode material powder obtained was confirmed by a powder X-ray diffraction pattern, the diffraction line from LiFePO ₄ was confirmed. The primary particle diameter D ₁ of the positive electrode material powder is 0.2 μm, the secondary particle diameter D ₂ is 0.5 μm, and the ratio D ₂ / D ₁ between the primary particle diameter D ₁ and the secondary particle diameter D ₂ is 2.5. Met.

(3) Evaluation of positive electrode material powder of lithium ion secondary battery The obtained positive electrode material powder and a solid electrolyte powder composed of Li ₂ S—P ₂ S ₅ (Molar ratio of Li ₂ S and P ₂ S ₅ 80:20 ) And acetylene black were mixed at a mass ratio of 40: 60: 6. 10 mg of the obtained mixture was pressed at a pressure of 360 MPa to obtain pellets (positive electrode) having a diameter of 10 mm and a thickness of about 50 μm.

Further, 80 mg of the solid electrolyte powder was pressed at a pressure of 360 MPa to obtain pellets (electrolyte layer) having a diameter of 10 mm and a thickness of 0.5 mm.

An all-solid lithium secondary battery was obtained by laminating an indium sheet having a thickness of 0.1 mm as the positive electrode and the electrolyte layer, and further pressing the electrode at a pressure of 240 MPa.

When charging / discharging was carried out at a current density of 13 μA / cm ² using the obtained secondary battery, the discharge capacity was 110 mAh / g, which was 65% of the theoretical capacity. The relationship between the discharge potential and the discharge capacity at this time is shown in FIG.

(Comparative Example 1)
Example 1 except that commercially available LiFePO ₄ (manufactured by Tianjin STL, D ₁ = 0.5 μm, D ₂ = 2.7 μm, D ₂ / D ₁ = 5.4) was used as the positive electrode material powder. Thus, an all solid lithium secondary battery was obtained.

When the obtained secondary battery was charged and discharged at a current density of 6.4 μA / cm ² , the discharge capacity was 40 mAh / g, which was 24% of the theoretical capacity. The relationship between the discharge potential and the discharge capacity at this time is shown in FIG.

(Comparative Example 2)
The crystallized glass was subjected to ball milling using Al ₂ O ₃ boulders with a diameter of ₂₀ mm for 5 hours, followed by ball milling in ethanol using ZrO ₂ boulders with a diameter of 5 mm for 15 hours to obtain crystals having an average particle diameter of 2 μm. A positive electrode material powder was obtained in the same manner as in Example 1 except that a vitrified glass powder was obtained. The primary particle diameter D ₁ of the obtained positive electrode material powder is 2 μm, the secondary particle diameter D ₁ is 2.6 μm, and the ratio D ₂ / D ₁ between the primary particle diameter D ₁ and the secondary particle diameter D ₂ is 1.3. there were.

Furthermore, using the obtained positive electrode material powder, an all solid lithium secondary battery was obtained in the same manner as in Example 1.

When the obtained secondary battery was charged and discharged at a current density of 13 μA / cm ² , the discharge capacity was 38 mAh / g, which was 22% of the theoretical capacity. The relationship between the discharge potential and the discharge capacity at this time is shown in FIG.

As is clear from Table 1 and FIGS. 1 to 3, the battery of Example 1 was excellent in discharge capacity of 110 mAh / g, whereas the batteries of Comparative Examples 1 and 2 were inferior in discharge capacity of 40 mAh / g or less. It was.

The positive electrode material powder for a lithium ion secondary battery and the positive electrode mixture powder for a lithium ion secondary battery of the present invention are electrodes of a lithium ion secondary battery used for portable electronic devices such as notebook computers and mobile phones, and electric vehicles. Suitable as a material.

Claims (6)

1. General formula: Li _x M _1-y M ′ _y (XO _z ) _n (x, y, z, n are 0 <x ≦ 2, 0 ≦ y <1, z = 3 or 4, 1 ≦ n ≦ 1 respectively. M is at least one transition metal in the first row of the periodic table, M ′ is at least one of Nb, Ta, Ge, Sn, Al, Ga, Zn, Mg or Cu, and X is S , P, B, or Si), and a lithium ion secondary battery positive electrode material powder containing a crystal represented by:
   The primary particle diameter D ₁ is less than or equal to 1.8 .mu.m, and a lithium ion secondary battery positive electrode, characterized in that the ratio D _{2 /} D ₁ of the primary particle diameter D ₁ and the secondary particle diameter D ₂ is 5 or less Material powder.
2. The lithium ion secondary battery positive electrode material powder according to claim 1, wherein M is Fe or Mn or a mixture thereof.
3. X is P, The lithium ion secondary battery positive electrode material powder of Claim 1 or 2 characterized by the above-mentioned.
4. A lithium ion secondary battery positive electrode mixture powder comprising the lithium ion secondary battery positive electrode material powder according to any one of claims 1 to 3 and a solid electrolyte powder.
5. The lithium ion secondary battery positive electrode mixture powder according to claim 4, wherein the solid electrolyte powder is a sulfide-based solid electrolyte powder.
6. A lithium ion secondary battery comprising a positive electrode containing the lithium ion secondary battery positive electrode mixture powder according to claim 4 and an electrolyte layer containing a solid electrolyte powder.
   

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