JP5245351B2 - Active material for lithium secondary battery and lithium secondary battery - Google Patents

Description

  The present invention relates to an active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery.

Conventionally, it is known to use olivine-type lithium iron phosphate (LiFePO ₄ ) as a positive electrode active material of a lithium secondary battery. When lithium iron phosphate is used as the positive electrode active material, the electron conductivity is lowered. However, by increasing the reaction surface area, the electron conductivity is increased and the reduction of the discharge capacity of the lithium secondary battery is prevented.

  For example, Patent Document 1 discloses a method of producing lithium iron phosphate using hot water treatment and a method of using it as an electrode material. When hot water treatment is used, the synthesis reaction proceeds by repeating dissolution and reprecipitation, so that it tends to be easy to obtain a composite having a small particle size, and the reaction surface area can be improved.

Patent Document 2 discloses a method for producing lithium iron phosphate by mixing iron powder, a lithium salt and a phosphate group compound and heating to 500 ° C. or higher. Since this method produces lithium iron phosphate using cheap iron powder, it can be produced at low cost. It was reported that the particle size of the lithium iron phosphate obtained at this time was 2 μm as observed by SEM photographs.
Special table 2007-511458 JP 2006-131485 A

  However, the manufacturing method described in Patent Document 1 has a problem in that the yield is low because the hot water treatment is performed. Further, when a lithium secondary battery is produced using lithium iron phosphate produced by the production method described in Patent Document 2 as a positive electrode active material, the discharge capacity at 0.1 C is 165 mAh / g, whereas at 2 C The discharge capacity was 123 mAh / g, and there was a problem that excellent discharge rate characteristics could not be obtained.

  The present invention has been made in view of the above-described problems, and provides a lithium secondary battery active material and a method for producing the same capable of obtaining excellent discharge rate characteristics, and also provides such a lithium secondary battery active material. The main object is to provide a lithium secondary battery as a positive electrode active material.

In order to achieve the above-described object, the present inventors have used lithium dihydrogen phosphate (LiH ₂ PO ₄ ) as the Li component and the PO ₄ component, and iron (II) oxalate dihydrate (FeC) as the Fe component. ₂ O ₄ .2H ₂ O) and lithium orthosilicate (Li ₄ SiO ₄ ) as the SiO ₄ component so that the molar ratio of Fe: PO ₄ : SiO ₄ is 1: 0.97: 0.03, respectively. The mixture was mixed, depressurized in a highly airtight tube furnace, purged with argon gas, fired at 600 ° C. for 12 hours, and cooled to room temperature and then crushed to produce an active material. When a secondary battery was produced, it was found that excellent discharge rate characteristics were obtained, and the present invention was completed.

That is, the first active material for a lithium secondary battery of the present invention includes an Li component, an M component (M is at least one metal element selected from the group consisting of Fe, Ni, Mn and Co), PO ₄ It is manufactured by firing a mixture containing a component and a grain growth inhibiting component that is at least one of an SiO ₄ component and an SO ₄ component, and crushing the resulting fired product.

In addition, the second active material for a lithium secondary battery of the present invention has a basic structure represented by LiMPO ₄ (M is at least one metal element selected from the group consisting of Fe, Ni, Mn, and Co). Includes at least one of SiO ₄ and SO ₄ .

  The lithium secondary battery of the present invention includes a positive electrode using the first or second active material for a lithium secondary battery of the present invention as a positive electrode active material, a negative electrode using a material that absorbs and releases lithium ions as a negative electrode active material, And an electrolyte containing lithium ions.

The method for producing an active material for a lithium secondary battery according to the present invention includes: (a) a Li component, an M component (M is at least one metal element selected from the group consisting of Fe, Ni, Mn, and Co); crushed ₄ and component, and the step of firing the mixture containing the grain growth inhibiting component is at least one of SiO ₄ components and SO ₄ component, the fired product obtained in (b) said step (a) And the step of performing.

  The first active material for a lithium secondary battery of the present invention has a particle size of about a few μm of comma, and excellent discharge rate characteristics are obtained when this is used as a positive electrode active material of a secondary battery. The reason why the active material for a lithium secondary battery has a particle size of about a few μm is not clear, but when the mixture is baked, the particle growth inhibiting component has the effect of suppressing the particle size growth. It is presumed that it was demonstrated.

The second active material for a lithium secondary battery of the present invention has a particle size of about a few μm comma, and excellent discharge rate characteristics can be obtained when this is used as a positive electrode active material of a secondary battery. Here, the second lithium secondary battery active material of the invention has included the grain growth inhibiting component is at least one of SiO ₄ and SO ₄ in a part of the composition, which is fired This is because the grain growth inhibitory component was contained in the previous mixture, and when the mixture was baked, the grain growth inhibitory component exerts an action of suppressing the growth of the grain size and has a particle size of about several μm comma. It is estimated that

  According to the lithium secondary battery of the present invention, excellent discharge rate characteristics can be obtained. The reason why such an effect can be obtained is not clear, but it is presumed that by using an active material for a lithium secondary battery having a small particle size, the surface area is increased and good discharge rate characteristics are obtained.

  According to the method for producing an active material for a lithium secondary battery of the present invention, lithium having a particle size of about a few μm in a high yield compared to the case of producing an active material for a lithium secondary battery by a hydrothermal synthesis method. An active material for a secondary battery is obtained. When this lithium secondary battery active material is used as a positive electrode active material of a secondary battery, excellent discharge rate characteristics can be obtained. The reason why an active material for a lithium secondary battery having a particle diameter of about several μm in this way is not certain, but when the mixture is fired, the particle growth inhibiting component has an effect of suppressing the growth of the particle diameter. It is estimated that

The first active material for a lithium secondary battery of the present invention includes an Li component, an M component (M is at least one metal element selected from the group consisting of Fe, Ni, Mn, and Co), a PO ₄ component, , A mixture containing a grain growth inhibiting component that is at least one of the SiO ₄ component and the SO ₄ component is fired, and the obtained fired product is crushed. The first method for producing an active material for a lithium secondary battery according to the present invention includes (a) an Li component and an M component (M is at least one metal selected from the group consisting of Fe, Ni, Mn, and Co). Element), a PO ₄ component, and a step of firing a mixture containing a grain growth inhibiting component that is at least one of an SiO ₄ component and an SO ₄ component; and (b) obtained in step (a). Crushing the fired product.

Here, as the Li component, for example, it may be a known lithium compound such as lithium carbonate (Li ₂ CO ₃₎ or lithium hydroxide (LiOH). As the PO ₄ component, for example, known phosphates such as ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) can be used. Thus may be a compound of the Li component and PO ₄ components, each containing individually, it is a compound containing both Li component and PO ₄ components preferably possible to reduce the number of weighing. Examples of such a compound include lithium dihydrogen phosphate (LiH ₂ PO ₄ ). As the M component, when the M component contains Fe, for example, known iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), iron (II) chloride (FeCl ₂ ), etc. These divalent iron compounds can be used. At this time, iron (II) oxalate dihydrate is more preferable. This is because iron (II) oxalate dihydrate is less corrosive to the gas generated during firing than iron (II) chloride. When the M component contains Ni, for example, a known divalent nickel compound such as nickel oxide (NiO) or nickel hydroxide (Ni (OH) ₂ ) can be used. Further, when the M component containing Mn, for example, may be used manganese carbonate (MnCO ₃₎ and manganese chloride tetrahydrate (MnCl ₂ · 4H ₂ O) known divalent manganese compound, such as. When the M component contains Co, for example, a known divalent cobalt compound such as cobalt oxide (CoO) or cobalt chloride (CoCl ₂ ) can be used. As the grain growth inhibiting component, when the grain growth inhibiting component contains a SiO ₄ component, for example, a known silicate such as lithium orthosilicate (Li ₄ SiO ₄ ) can be used. When the grain growth inhibiting component contains an SO ₄ component, for example, known sulfates such as iron (II) sulfate heptahydrate (FeSO ₄ .7H ₂ O) and lithium sulfate (Li ₂ SO ₄ ). Can be used. As the grain growth inhibiting component, it is more preferable to use the SiO ₄ component than the SO ₄ component because the decrease in the discharge capacity is small. Moreover, each component is not limited to what was listed here.

  In order to adjust the mixture containing these components, the proportion of Fe in the M component is preferably 80% or more. This is because Fe is abundant as a resource and is inexpensive. Moreover, it is preferable to adjust the quantity of the grain growth inhibitory component contained in the mixture so as to be an olivine type single phase lithium compound. Specifically, it is preferable that the grain growth inhibiting component is 0.01 to 0.2 mol with respect to 1 mol of the M component. When the grain growth inhibiting component is 0.2 mol or more, it is not preferable because it does not become an olivine type single phase, and when it is less than 0.01 mol, the grain growth inhibiting effect may not be obtained sufficiently, which is not preferred. The grain growth inhibiting component is more preferably 0.01 to 0.05 mol, for example 0.03 mol, relative to 1 mol of the M component. By doing so, since it becomes an olivine type single phase, it is excellent in safety, and a sufficient discharge capacity can be secured while obtaining the effect of suppressing grain growth. Any of these components can be used in a powder form, and mixing can be performed by a method used for mixing ordinary powders. Specific examples include, but are not limited to, a method of mixing using a ball mill, a mixer, a mortar, or the like.

  For firing the mixture containing these components, there is no particular limitation. For example, the firing temperature is preferably 400 ° C. or higher, more preferably 600 ° C. or higher and 800 ° C. or lower. A calcination temperature of less than 400 ° C. is not preferable because the reaction does not proceed sufficiently and the crystallinity deteriorates. Further, firing at 800 ° C. or higher is not preferable because grain growth is promoted and the particle diameter is increased. The firing time is not particularly limited as long as it is sufficient to complete the firing of the mixture. For example, it is preferably about 12 hours. Firing is preferably performed in an environment where oxygen is not present, such as in an inert atmosphere. If firing is performed in an environment where oxygen is present, part of iron becomes trivalent and discharge capacity decreases, which is not preferable. Specifically, it is not particularly limited, and examples thereof include a rare gas group element gas stream such as helium gas, neon gas, and argon gas, and an inert gas stream such as nitrogen gas. At this time, since argon gas is heavier than oxygen, it is more preferable to perform under argon gas flow.

  The fired product containing these components is considered to be obtained as an aggregate of primary particles having a particle size of about several μm comma, with the growth of the particle size being suppressed by the particle growth suppressing component. Therefore, it is preferable to increase the electronic conductivity by mixing with a conductive material. For this reason, it is preferable to crush the fired product. The method for pulverizing the fired product is not particularly limited as long as it can be pulverized to such an extent that it can be sufficiently mixed with a conductive material described later. For example, a ball mill, a mixer, a mortar, etc. The method to use is mentioned.

  The first active material for a lithium secondary battery of the present invention may be a result obtained by the production method described herein, or another production method as long as it is substantially the same as this result. It may be obtained by.

The second active material for a lithium secondary battery of the present invention has a basic structure represented by LiMPO ₄ (M is at least one metal element selected from the group consisting of Fe, Ni, Mn, and Co), and has one composition. The part contains at least one of SiO ₄ and SO ₄ . Such an active material for a lithium secondary battery includes, for example, a Li component, an M component (M is at least one metal element selected from the group consisting of Fe, Ni, Mn, and Co), a PO ₄ component, and SiO _4. It is presumed that it can be obtained by firing a mixture containing a grain growth inhibiting component that is at least one of the components and the SO ₄ component and crushing the obtained fired product.

  It is preferable that the 1st and 2nd active material for lithium secondary batteries of this invention is an olivine type single phase. The olivine type structure is based on the hexagonal close-packed packing of oxygen, in which phosphorus is located at the tetrahedral site and lithium and M are located at the octahedral site, and such a structure is highly stable. preferable. When this active material for lithium secondary batteries having an olivine type single phase structure is used as a positive electrode active material for a lithium secondary battery, it is difficult to release oxygen, so that a lithium secondary battery excellent in safety can be manufactured.

  In the first and second active materials for a lithium secondary battery of the present invention, M is preferably Fe. This is because Fe is abundant as a resource and is inexpensive.

  The lithium secondary battery of the present invention includes a positive electrode using the active material for a lithium secondary battery as described above as a positive electrode active material, a negative electrode using a material that absorbs and releases lithium ions as a negative electrode active material, and lithium ions. And an electrolyte containing.

  In the lithium secondary battery of the present invention, the positive electrode may contain a conductive material. The conductive material is not particularly limited as long as it is a conductive material. For example, carbon blacks such as ketjen black, acetylene black, channel black, furnace black, lamp black and thermal black may be used, and natural graphite such as flake graphite, graphite such as artificial graphite and expanded graphite may be used. Further, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper, silver, nickel, and aluminum, or organic conductive materials such as polyphenylene derivatives may be used. These may be used alone or in combination.

  In the lithium secondary battery of the present invention, the positive electrode may contain a binder. Although it does not specifically limit as a binder, A thermoplastic resin, a thermosetting resin, etc. are mentioned. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer ( FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer ( ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene- Rollotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, etc. Is mentioned. These materials may be used alone or in combination.

  In the lithium secondary battery of the present invention, the negative electrode is not particularly limited as long as it contains a material that absorbs and releases lithium ions as a negative electrode active material. Here, examples of materials that occlude and release lithium ions include metal lithium and lithium alloys, metal oxides, metal sulfides, and carbonaceous substances that occlude and release lithium ions. Examples of the lithium alloy include alloys of lithium with aluminum, silicon, tin, magnesium, indium, calcium, and the like. Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. As the carbonaceous material that occludes and releases lithium ions, for example, hard carbon and soft carbon can be used, or natural or artificial graphite, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, gas phase, and the like. A mixture of carbon fiber, a fired organic compound such as phenol resin, coke, or the like can be used.

In the lithium secondary battery of the present invention, the electrolyte is not particularly limited, but an electrolytic solution containing a supporting salt, a gel electrolyte, a solid electrolyte, or the like can be used. Examples of the supporting salt include known supports such as LiPF ₆ , LiClO ₄ , LiBF ₄ , Li (CF ₃ SO ₃ ), LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ). A salt can be used. As a solvent for the electrolytic solution, for example, an aprotic organic solvent can be used. Examples of such an organic solvent include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers, and the like. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, and vinyl carbonate. Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate. Examples of the cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. These may be used alone or in combination. The gel electrolyte is not particularly limited. For example, a polymer such as polyvinylidene fluoride, polyethylene glycol, or polyacrylonitrile, or a saccharide such as an amino acid derivative or sorbitol derivative is added with an electrolyte containing a supporting salt. And a gel electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes. Well-known inorganic solid electrolytes include, for example, Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. These may be used alone or in combination. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination.

  The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the lithium secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a thin fine olefin resin such as polyethylene or polypropylene is used. A porous membrane is mentioned. These may be used alone or in combination.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. Regardless of which shape is used, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the electrode body is electrically connected between the positive electrode and the negative electrode to the positive electrode terminal and the negative electrode terminal. Can be sealed in a battery case together with an electrolyte to complete the battery.

  Hereinafter, specific examples of the present invention will be described using examples.

[Example 1]
Lithium dihydrogen phosphate (LiH ₂ PO ₄ ) as the Li component and PO ₄ component, iron (II) oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O) as the Fe component, and orthosilicate as the SiO ₄ component Lithium acid (Li ₄ SiO ₄ ) was precisely weighed so that the molar ratio of Fe: PO ₄ : SiO ₄ was 1: 0.97: 0.03, respectively. Next, after thoroughly mixing these together with ethanol using a ball mill, the powder obtained by volatilizing ethanol and pulverizing with a mortar was pelletized at a pressure of 1 t / cm ² to obtain a sample for firing. The sample for firing was decompressed in a highly airtight tubular furnace, and after being replaced with argon gas, was fired at 600 ° C. for 12 hours. Then, after lowering to room temperature, it was crushed in a mortar to obtain a powder sample. During firing, argon gas was allowed to flow at 30 ml / min in a highly airtight tubular furnace.

When the powder sample thus obtained was measured with an X-ray diffractometer (manufactured by Rigaku Corporation, RINT-2200), a result as shown in FIG. 1 was obtained. FIG. 1 shows the measurement results of the X-ray diffractometer, with the horizontal axis representing the diffraction angle and the vertical axis representing the intensity. As is clear from FIG. 1, since the peak pattern coincided with LiFePO _{4 of} Comparative Example 1 described later, which is known to be an olivine type single phase, this powder sample is an olivine type single phase. Was confirmed. Next, when this powder sample was observed using a scanning electron microscope (manufactured by Hitachi, Ltd., S-4300), an image as shown in FIG. 2A was obtained. FIG. 2 is a scanning electron micrograph. For all the particles in FIG. 2 (a), that is, for each particle included in a photograph taken in the range of 35 μm in length and 50 μm in width in a focused state, the longest diameter and the shortest diameter are visually measured. Then, when the average value of these two values was taken as the particle size of one particle and the average value of all the particle sizes contained in the photograph was determined, this value was about 0.1 μm.

The powder sample thus obtained, carbon black (manufactured by Tokai Carbon Co., Ltd., # TB-5500) and polytetrafluoroethylene were mixed so that the weight percentage was 70: 25: 5, and 14 mg of the mixed powder was mixed. It formed into a φ10 mm pellet. And the coin-type cell 20 was assembled using this pellet. FIG. 3 is a cross-sectional view schematically showing the configuration of the coin cell 20. The coin-type cell 20 was assembled in the following procedure. That is, a battery case 21 made of SUS304 is prepared, a positive electrode 22 is arranged at the lower part of the battery case 21, and a lithium metal having a diameter of 14 mm and a thickness of 0.4 mm as a negative electrode 23 at a position facing through a polypropylene separator 24. Arranged. On the other hand, a solution prepared by adding 1 M of LiPF ₆ to a mixture of ethylene carbonate and diethyl carbonate so that the volume ratio was 3: 7 was prepared, and this was used as an electrolytic solution. Then, a PTFE gasket 25 was placed in the battery case 21, and 0.2 ml of electrolyte was injected and impregnated. Finally, a sealing plate 26 made of SUS304 was placed in the opening of the battery case 21, and the end of the battery case 21 was crimped to seal the battery case 21, thereby producing a coin-type cell 20.

Evaluation was performed using the coin-type cell 20 produced in this manner. First, constant current charging was performed at a current density of 0.2 mA / cm ² until reaching 4.2 V, and then constant current discharging was performed while changing the current density until the final voltage reached 2.0 V. In addition, the current density of the constant current discharge was adjusted so as to be four stages of 0.1C, 1C, 2C, and 5C. Moreover, evaluation was performed at 20 degreeC. The evaluation results at this time are shown in Table 1. As is clear from Table 1, the discharge capacity at 0.1 C was 169 mAh / g, which was almost theoretical capacity, the discharge capacity at 2 C was 162 mAh / g, and the discharge capacity at 5 C was 158 mAh / g. From this, it can be seen that the discharge capacity hardly decreases even when the output during discharge is increased. For this reason, it can be said that it has the outstanding discharge rate characteristic.

[Example 2]
Powder sample in the same manner as in Example 1, except that lithium orthosilicate used as the SiO ₄ component in Example 1 was replaced with iron (II) sulfate heptahydrate (FeSO ₄ .7H ₂ O) as the SO ₄ component Adjusted. When this powder sample was measured for X-ray diffraction under the same conditions as in Example 1, the results shown in FIG. 1 were obtained. From this result, it was found that it was an olivine type single phase as in Example 1. Next, observation with a scanning electron microscope was performed under the same conditions as in Example 1. As a result, an image as shown in FIG. 2B was obtained. With respect to this result, when the average value of the particle diameters was determined in the same manner as in Example 1, this value was about 0.1 μm.

Using this powder sample, a coin-type cell was produced in the same manner as in Example 1, and this coin-type cell was evaluated under the same conditions as in Example 1. The evaluation results at this time are shown in Table 1. As is apparent from Table 1, the discharge capacity at 0.1 C was almost theoretical capacity of 168 mAh / g, the discharge capacity at 2 C was 160 mAh / g, and the discharge capacity at 5 C was 153 mAh / g. From this, it can be said that even if the SiO ₄ component is changed to the SO ₄ component, it has excellent discharge rate characteristics.

[Comparative Example 1]
A powder sample was prepared in the same manner as in Example 1 except that lithium orthosilicate used as the SiO ₄ component in Example 1 was not added and the Fe: PO ₄ molar ratio was precisely adjusted to 1: 1. did.

Although it is well known that this powder sample is an olivine type single phase, when X-ray diffraction was measured under the same conditions as in Example 1, the results shown in FIG. 1 were obtained. That is, the peak pattern of Comparative Example 1 in FIG. 1 is an olivine type single phase. Next, observation with a scanning electron microscope was performed under the same conditions as in Example 1. As a result, an image as shown in FIG. 2C was obtained. With respect to this result, the average value of the particle diameter was determined in the same manner as in Example 1, and this value was about 1.0 μm. From this, it can be said that the SiO ₄ component or the SO ₄ component used in Examples 1 and 2 helps to reduce the particle size.

  Using this powder sample, a coin-type cell was produced in the same manner as in Example 1, and this coin-type cell was evaluated under the same conditions as in Example 1. The evaluation results at this time are shown in Table 1. As is clear from Table 1, the discharge capacity at 0.1 C was 170 mAh / g, which was almost theoretical, but the discharge capacity at 2 C was 125 mAh / g, and the discharge capacity at 5 C was 80 mAh / g. From this, it can be seen that the discharge capacity greatly decreases when the output during discharge is increased. For this reason, it can be said that excellent discharge rate characteristics cannot be obtained in Comparative Example 1.

[Example 3]
A powder sample was prepared in the same manner as in Example 1, except that the molar ratio of Fe: PO ₄ : SiO ₄ in Example 1 was precisely adjusted to 1: 0.80: 0.20. When this powder sample was measured for X-ray diffraction under the same conditions as in Example 1, the results shown in FIG. 1 were obtained. From this result, it can be seen that there are many peaks that cannot be assigned to the olivine-type single-phase peak, so that some by-product is generated instead of the olivine-type single phase. Next, observation with a scanning electron microscope was performed under the same conditions as in Example 1. As a result, an image as shown in FIG. 2D was obtained. With respect to this result, when the average value of the particle diameters was determined in the same manner as in Example 1, this value was about 0.1 μm. From this, it can be said that the particle size is reduced by mixing and baking the SiO ₄ component.

  Using this powder sample, a coin-type cell was produced in the same manner as in Example 1, and this coin-type cell was evaluated under the same conditions as in Example 1. The evaluation results at this time are shown in Table 1. As is apparent from Table 1, the discharge capacity at 0.1 C was 108 mAh / g, which was lower than the theoretical charge capacity, but the discharge capacity at 2 C was 92 mAh / g, and the discharge capacity at 5 C was 72 mAh / g. From this, it can be said that it has excellent discharge rate characteristics as compared with Comparative Example 1.

[Example 4]
A powder sample was prepared in the same manner as in Example 1, except that the molar ratio of Fe: PO ₄ : SO ₄ in Example 2 was precisely weighed so as to be 1: 0.80: 0.20. When this powder sample was measured for X-ray diffraction under the same conditions as in Example 1, the results shown in FIG. 1 were obtained. From this result, it is understood that some by-product is generated instead of the olivine type single phase as in Example 3. Next, observation with a scanning electron microscope was performed under the same conditions as in Example 1. As a result, an image as shown in FIG. With respect to this result, when the average value of the particle diameters was determined in the same manner as in Example 1, this value was about 0.1 μm. From this, it can be said that the particle size is reduced by mixing and firing SO ₄ .

  Using this powder sample, a coin-type cell was produced in the same manner as in Example 1, and this coin-type cell was evaluated under the same conditions as in Example 1. The evaluation results at this time are shown in Table 1. As is apparent from Table 1, the discharge capacity at 0.1 C was 103 mAh / g, which was lower than the theoretical charge capacity, but the discharge capacity at 2 C was 88 mAh / g, and the discharge capacity at 5 C was 70 mAh / g. From this, it can be said that it has excellent discharge rate characteristics as compared with Comparative Example 1.

  In each of the above-described embodiments, the case where the metal element M is Fe has been described. However, even though Ni, Co, and Mn have the same ionic radius as Fe, the metal element M is Fe. In addition to Ni, Co, or Mn, or even if the metal element M is not Fe but Ni, Co, or Mn, It is easy to analogize that the effect is obtained.

It is a graph showing the spectrum of a X-ray-diffraction measurement. It is a scanning electron micrograph. 2 is a cross-sectional view illustrating an outline of the configuration of a coin-type cell 20. FIG.

Explanation of symbols

  20 coin cell, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate.

Claims (2)

It is manufactured by firing a mixture containing a Li component, an Fe component, a PO ₄ component, and a grain growth inhibiting component that is a SiO ₄ component, and crushing the obtained fired product,
The mixture includes 0.01 to 0.05 mol of the grain growth inhibiting component with respect to 1 mol of Fe component,
The firing is performed in an inert gas atmosphere,
Olivine single phase der is, the basic structure is represented by LiFePO _4,
Active material for lithium secondary battery. A positive electrode using the active material for a lithium secondary battery according to claim 1 as a positive electrode active material;
A negative electrode using a material that absorbs and releases lithium ions as a negative electrode active material;
An electrolyte containing lithium ions;
Rechargeable lithium battery.

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