Method for producing lithium-based polyanion particles for positive electrode active material of lithium-ion secondary battery

Abstract

The present invention pertains to a method for manufacturing lithium-based polyanion particles for a positive electrode active material of a lithium-ion secondary battery. The method is highly safe and provides simplified steps as a process for regenerating used lithium-ion batteries. Specifically, the present invention is a method for producing lithium-based polyanion particles for a positive electrode active material of a lithium-ion secondary battery, the method using a powder (X) that contains degraded lithium-based polyanion particles (A') and that is obtained from a used lithium ion secondary battery constituted by a positive electrode containing lithium-based polyanion particles (A) that carry carbons. The method does not use a reducing agent and comprises: a step (I) for mixing the powder (X) and a lithium source (Y) to obtain slurry water I; a step (II) for adjusting the pH of the slurry water I that has been obtained to 9-14 to obtain slurry water II; and a step (III) for subjecting the slurry water II that has been obtained to a heating process at a temperature of at least 30°C but lower than 200°C for 3 to 5 hours. The lithium-based polyanion particles (A) are represented by formula (A): LiaMnbFecMxPO4, and the degraded lithium-based polyanion particles (A') are represented by formula (A), where the molar ratio of Li to P, which is Li / P, is at least 0.3 but less than 1.

Description

Method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium-ion secondary batteries

[0001] The present invention relates to a method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium ion secondary batteries, which allows for the effective utilization of used lithium ion secondary batteries.

[0002] Secondary batteries such as lithium-ion secondary batteries are used in a wide range of fields, including mobile phones, digital cameras, notebook PCs, hybrid vehicles, and electric vehicles. ｘ Fe １－ｘ P.O. ４ Due to their high safety and large capacity, lithium-based polyanion particles such as these are extremely useful as cathode materials for lithium-ion secondary batteries. Recently, environmental awareness has increased worldwide, and efforts to address resource depletion are being made. Therefore, there is a strong demand for recycling used lithium-ion batteries, and various attempts have been made to regenerate cathode materials.

[0003] For example, Non-Patent Document 1 describes the use of used LiFePO ４ A regeneration process for the cathode material is disclosed, which involves the use of N as a reducing agent under hydrothermal conditions while replenishing lithium. ２ H ４ ・H ２ Furthermore, Patent Document 1 discloses a method for selectively oxidizing and reducing waste lithium iron phosphate to regenerate it, in which lithium and carbon are added and the composition is adjusted by primary sintering and secondary sintering under specific conditions.

[0004] Special Publication No. 2022-517160

[0005] Qiankun Jing et al., "Direct Regeneration of Spent LiFePO4 Cathode Material by a Green and Efficient One-Step Hydrothermal Method", ACS Sustainable Chemical Engineering, 2020, Vol 8, No. 48, 17622-17628

[0006] However, the technology described in Non-Patent Document 1 requires harsh treatment conditions and consideration must be given to the toxicity of the reducing agent, so there is still room for improvement before it can be commercialized. Furthermore, even with the technology described in Patent Document 1, the treatment process is still inevitably complicated.

[0007] Therefore, the present invention relates to a method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium ion secondary batteries, which is highly safe and can simplify the process for recycling used lithium ion batteries.

[0008] Therefore, the present inventors conducted extensive research to solve the above problems, and as a result, they discovered a manufacturing method that can effectively regenerate deteriorated lithium-based polyanion particles by using powder obtained from the positive electrodes of used lithium-ion secondary batteries as a raw material and going through a simple process of subjecting the prepared slurry water to specific conditions without using a reducing agent.

[0009] That is, the present invention provides a method for producing lithium-based polyanion particles for a positive electrode active material of a lithium ion secondary battery, the method comprising the following steps (I) to (III): (I) mixing the powder (X) and a lithium source (Y) to obtain slurry water I; (II) adjusting the pH of the obtained slurry water I to 9 to 14 to obtain slurry water II; and (III) subjecting the obtained slurry water II to a heat treatment at a temperature of 30° C. or higher but lower than 200° C. for 3 to 5 hours, wherein the lithium-based polyanion particles (A) are represented by the following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ P.O. ４...(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd; a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0<b≦1.2, 0<c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3), wherein the deteriorated lithium-based polyanion particles (A') are represented by formula (A) and have a molar ratio of Li to P (Li / P) of 0.3 or more and less than 1.

[0010] According to the method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium-ion secondary batteries of the present invention, it is possible to obtain lithium-based polyanion particles that are highly useful as a positive electrode material for lithium-ion secondary batteries that exhibit excellent battery properties, while being a highly safe and simple method that does not use a reducing agent. Therefore, the present invention can greatly contribute to the realization of recycling used lithium-ion secondary batteries.

[0011] FIG. 1 is a pattern diagram showing the analysis results of an XRD pattern.

[0012] The present invention will be described in detail below. The method for producing lithium-based polyanion particles for use as a positive electrode active material in a lithium-ion secondary battery of the present invention uses a powder (X) containing degraded lithium-based polyanion particles (A') obtained from the positive electrode of a used lithium-ion secondary battery constructed with a positive electrode containing carbon-supported lithium-based polyanion particles (A) represented by formula (A) (hereinafter also referred to simply as "lithium-based polyanion particles (A)"). That is, a used lithium-ion secondary battery constructed with a positive electrode produced using lithium-based polyanion particles (A) as a single material gradually loses lithium during use, resulting in a degraded state, and is therefore discarded after use. However, in the production method of the present invention, the positive electrode of such a used lithium-ion secondary battery is subjected to a process such as pulverization to produce powder (X), and the powder (X) containing the degraded lithium-based polyanion particles (A') is used as one of the raw materials. In other words, the method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium ion secondary batteries according to the present invention is a method for regenerating deteriorated lithium-based polyanion particles (A').

[0013] According to the present invention, the depleted lithium of the depleted lithium-based polyanion particles (A') (hereinafter also referred to as "lithium-based polyanion particles (A')") contained in the powder (X) can be effectively replenished and regenerated into the lithium-based polyanion particles (A) represented by formula (A) (hereinafter also referred to as "initial lithium-based polyanion particles (A)") originally contained in the positive electrode. Therefore, the lithium-based polyanion particles (hereinafter also referred to as "regenerated lithium-based polyanion particles") obtained by the present invention can be effectively utilized as a positive electrode material for constructing a lithium ion secondary battery with excellent battery characteristics. The regenerated lithium-based polyanion particles obtained by the present invention are particles regenerated into the lithium-based polyanion particles (A), and like the initial lithium-based polyanion particles (A), they are lithium-based polyanion particles represented by formula (A). However, they may have the same composition as the initial lithium-based polyanion particles (A), or they may have a different composition as long as they are represented by formula (A). Therefore, for example, the regenerated lithium-based polyanion particles obtained by the present invention may be adjusted so that b, c, etc. in formula (A) are appropriately adjusted to desired values.

[0014] The lithium-based polyanion particles (A) are particles supported on carbon and represented by the following formula (A), and are so-called olivine-type lithium transition metal phosphate compounds containing at least both manganese (Mn) and iron (Fe) as transition metals. ａ Mn ｂ Fe ｃ M ｘ P.O. ４ ... (A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0<b≦1.2, 0<c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.)

[0015] In the above formula (A), M may further be Mg, Al, Ti, Zn, Nb, Co, Zr, or Gd from the viewpoint of recycling as a highly useful material that can improve battery characteristics. Furthermore, a is preferably 0.6≦a≦1.2, more preferably 0.65≦a≦1.15, and even more preferably 0.7≦a≦1.1. b is preferably 0.4≦b≦0.8. c is preferably 0.2≦c≦0.6. x may be 0≦x≦0.2, or may be 0≦x≦0.15, or may be 0≦x≦0.1.

[0016] Specifically, for example, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.75 Fe 0.15 Mg 0.1 PO4, LiMn 0.75 Fe 0.19 Zr 0.03 PO4, LiMn 0.85 Fe 0.15 PO4, LiMn 0.5 Fe 0.5 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4, Li 0.6 Mn 0.84 Fe 0.36 PO4, Li 0.83 Mn 0.8 Fe 0.2 PO4, etc. Among them, Li 0.83 Mn 0.8 Fe 0.2 PO4, LiMn 0.4 Fe 0.6 P.O. ４ , LiMn 0.45 Fe 0.55 P.O.４ , LiMn 0.7 Fe 0.3 P.O. ４ , LiMn 0.8 Fe 0.2 P.O. ４ , LiMn 0.6 Fe 0.4 P.O. ４ , Li 1.2 Mn 0.63 Fe 0.27 P.O. ４ is preferred.

[0017] The crystallite diameter of the lithium-based polyanion particles (A) is usually 1000 nm or less, preferably 1 nm to 1000 nm, more preferably 25 nm to 1000 nm, even more preferably 27.5 nm to 700 nm, and still more preferably 30 nm to 500 nm. The crystallite diameter refers to the value determined by applying the Scherrer equation to the full angle of the XRD pattern.

[0018] The carbon material forming the carbon supported on the lithium-based polyanion particles (A) is not particularly limited, but typically includes one or more selected from cellulose nanofibers and water-soluble carbon materials. These cellulose nanofibers and water-soluble carbon materials are carbonized to form carbon, which is then supported on the lithium-based polyanion particles (A) as cellulose nanofiber-derived carbon or water-soluble carbon material-derived carbon. Examples of cellulose nanofibers include those with a fiber diameter of 1 nm to 1,000 nm. Examples of water-soluble carbon materials include monosaccharides such as glucose, fructose, galactose, and mannose; disaccharides such as maltose, sucrose, and cellobiose; polysaccharides such as starch and dextrin; polyols and polyethers such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, butanediol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid and tartaric acid. Other carbon materials include, for example, water-insoluble carbon materials such as carbon nanofiber, graphite, and carbon black such as ketjen black and acetylene black.

[0019] On the other hand, the powder (X) used in the production method of the present invention is a powder obtained from the positive electrode of a used lithium ion secondary battery constructed with a positive electrode containing carbon-supported lithium-based polyanion particles (A), and contains deteriorated lithium-based polyanion particles (A'). That is, since the positive electrode constituting the lithium ion secondary battery before use contained the lithium-based polyanion particles (A) represented by formula (A), the powder (X) obtained from the positive electrode of the used lithium ion secondary battery contains the lithium-based polyanion particles (A) in a deteriorated state as lithium-based polyanion particles (A').

[0020] However, in the manufacturing method of the present invention, from the viewpoint of realizing a highly useful and effective recycling process to obtain lithium-based polyanionic particles (A), a powder (X) containing specific lithium-based polyanionic particles (A') is treated. That is, the lithium-based polyanionic particles (A') are represented by the above formula (A) like the lithium-based polyanionic particles (A), and have a molar ratio of Li to P (Li / P) of 0.3 or more and less than 1. From the viewpoint of realizing an effective recycling process to obtain lithium-based polyanionic particles (A') having a stable crystal structure, the molar ratio of Li to P (Li / P) in the lithium-based polyanionic particles (A') is preferably 0.4 or more and less than 1, more preferably 0.45 or more and less than 1, even more preferably 0.5 or more and less than 1, still more preferably 0.55 or more and less than 1, and even more preferably 0.55 or more and less than 0.95. The molar ratio of Li to P (Li / P) is calculated from the values ​​of the molar amount of Li and the molar amount of P determined by performing ICP analysis using an ICP optical emission spectrometer.

[0021] The crystallite diameter of the lithium-based polyanionic particles (A') is usually 1000 nm or less, and may be 1 nm to 1000 nm, 20 nm to 1000 nm, 30 nm to 600 nm, 30 nm to 300 nm, or 50 nm to 200 nm. Note that, as with the lithium-based polyanionic particles (A), the crystallite diameter refers to the value determined by applying the Scherrer equation to the full angle of the XRD pattern.

[0022] The method for obtaining the powder (X) from the recovered used lithium ion secondary batteries is not particularly limited, and may be, for example, by disassembling, crushing, roasting, etc. the used lithium ion secondary batteries to extract the positive electrodes, which may then be subjected to processing such as pulverization, gravity separation, etc. The powder (X) may also be obtained in the form of a slurry water using water as an appropriate solvent.

[0023] In the present invention, if powder (X) is obtained by recovering a used lithium-ion secondary battery constructed with a positive electrode made of lithium-based polyanionic particles (A) as a positive electrode material, the molar ratio (Li / P) of Li to P in powder (X) can be considered to be the same as the molar ratio (Li / P) of Li to P in lithium-based polyanionic particles (A'). Therefore, the molar ratio (Li / P) value determined by performing the ICP analysis using powder (X) may be used as the molar ratio (Li / P) in lithium-based polyanionic particles (A').

[0024] The method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium-ion secondary batteries of the present invention specifically includes the following steps (I) to (III): (I) mixing powder (X) and a lithium source (Y) to obtain slurry water I; (II) adjusting the pH of the obtained slurry water I to 9 to 14 to obtain slurry water II; and (III) subjecting the obtained slurry water II to a heat treatment at a temperature of 30°C or higher but lower than 200°C for 3 to 5 hours. This method does not use a reducing agent. In other words, because no reducing agent is used, there is no need to consider the toxicity of such a reducing agent, effectively simplifying the process while improving safety. Specific examples of such reducing agents include hydrazine, sodium sulfite, sodium thiosulfate, ascorbic acid, or salts thereof.

[0025] Step (I) is a step of mixing powder (X) and a lithium source (Y) to obtain slurry water I. As described above, powder (X) is a powder obtained from the positive electrode of a used lithium ion secondary battery, and the powder itself may be used directly, or slurry water containing powder (X) may be used.

[0026] The lithium source (Y) is a lithium supply material for replenishing lithium that has been removed from the lithium-based polyanion particles (A') contained in the powder (X). Usable lithium sources (Y) include hydroxides (e.g., LiOH·HO, LiOH), sulfates, carbonates, acetates, and nitrates. Among these, hydroxides are preferred. The amount of lithium source (Y) added may vary depending on the composition and amount of the lithium-based polyanion particles (A'). However, it may be adjusted appropriately based on the composition of the lithium-based polyanion particles represented by formula (A) to be obtained by the present invention, while performing ICP analysis using an ICP emission spectrometer as needed.

[0027] In step (I), in order to facilitate effective regeneration of the lithium-based polyanion particles (A'), it is preferable to further mix carbon (C) in addition to the powder (X) and the lithium source (Y). In particular, when the heat treatment to be performed in step (III) described below is performed at a low temperature, mixing carbon (C) here provides an even more effective effect.

[0028] Examples of usable carbon (C) include one or more types of carbon powder (c1) selected from Ketjen black, acetylene black, and graphite powder; carbon sheet (c2); lump graphite (c3); carbon rod (c4); and carbon felt (c5).

[0029] When carbon powder (c1) is used as carbon (C), one or two types selected from Ketjen black and acetylene black are preferred. Furthermore, from the viewpoint of more effectively regenerating the lithium-based polyanion particles, the average particle size of the carbon powder (c1) is preferably 25 nm to 20,000 nm, more preferably 30 nm to 11,000 nm. The average particle size refers to the average value of the particle sizes (major axis lengths) of 100 randomly selected particles observed under an SEM or TEM electron microscope. The amount of carbon powder (c1) added is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the powder (X) used in step (I).

[0030] The carbon sheet (c2) is a carbon material in the form of a sheet made of carbon fibers, which can be cut to a desired size (surface area) as needed. When the carbon sheet (c2) is used as the carbon (C), the amount of the carbon sheet (c2) added is preferably 1 to 20 parts by mass, more preferably 2 to 18 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the powder (X) used.

[0031] The massive graphite (c3) is a carbon material that is in the form of massive particles having a particle size of about 3 cm to 5 cm and can be used after being subjected to appropriate treatment such as pulverization as necessary. When the massive graphite (c3) is used as the carbon (C), the amount of the massive graphite (c3) added is preferably 5 parts by mass to 30 parts by mass, more preferably 5 parts by mass to 25 parts by mass, and even more preferably 10 parts by mass to 25 parts by mass, per 100 parts by mass of the powder (X) used.

[0032] The carbon rod (c4) has a rod shape with a diameter of about 5 mm to 50 mm, can be cut to the desired length as needed, and can be used by fixing it to a reaction vessel or the like when in use. When using a carbon rod (c4) as carbon (C), the amount of the carbon rod (c4) added is preferably 5 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 to 25 parts by mass, relative to 100 parts by mass of the powder (X) used.

[0033] The carbon felt (c5) is a carbon material in the form of felt having a thickness of about 1 mm to 5 mm, which is made by intertwining fibers at a high density. When the carbon felt (c5) is used as the carbon (C), the amount of the carbon felt (c5) added is preferably 1 to 20 parts by mass, more preferably 2 to 18 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the powder (X) used.

[0034] Among the carbons (C), it is preferable to use one or more selected from carbon powder (c1) and carbon sheet (c2), and it is more preferable to use carbon powder (c1) from the viewpoint that recovery during or after the treatment is not required.

[0035] In step (I), depending on the composition of the lithium-based polyanionic particles (A) to be obtained by the present invention and the composition of the lithium-based polyanionic particles (A') used, a manganese compound, an iron compound, or a compound of a metal other than a manganese compound and an iron compound (M: M has the same meaning as M in formula (A)) may be appropriately added. In this case, if there is a phosphorus deficiency, a phosphate compound may also be appropriately added. Examples of usable manganese compounds include manganese acetate, manganese nitrate, manganese sulfate, etc. Examples of usable iron compounds include iron acetate, iron nitrate, iron sulfate, etc. Examples of usable phosphate compounds include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, etc.

[0036] In step (I), when the powder (X) and the lithium source (Y) are mixed, there is no particular limitation on the order of addition, but from the viewpoint of more effectively replenishing the separated lithium, it is preferable to add the lithium source (Y) and then the powder (X). Also, when carbon (C) is further mixed in step (I), there is no particular limitation on the order of addition, but it is preferable to add the carbon powder (C) after mixing the powder (X) and the lithium source (Y).

[0037] To obtain the slurry water I, in addition to the powder (X) and the lithium source (Y), water may be used as a solvent. As described above, when the powder (X) is used in the form of slurry water, the slurry water I can be obtained without adding additional water. The slurry water I is preferably pre-stirred before proceeding to the next step (II). This effectively promotes lithium replenishment. The stirring time is preferably 1 to 60 minutes, more preferably 5 to 30 minutes, and even more preferably 10 to 20 minutes.

[0038] From the viewpoint of effectively suppressing unnecessary elution of lithium-based polyanion particles from the powder (X) and achieving efficient regeneration, the pH of the slurry water I is preferably 7 or higher, more preferably 8 to 14, and even more preferably 8.5 to 13. For adjusting the pH, a known pH adjuster such as sodium hydroxide or potassium hydroxide may be used as appropriate.

[0039] In step (I), for example, when powder (X) is used in the form of a slurry water, it is desirable to consistently adjust the pH of the slurry water to within the above range throughout step (I), thereby more effectively suppressing unnecessary elution of lithium-based polyanion particles from powder (X) and enabling efficient regeneration of lithium-based polyanion particles.

[0040] Step (II) is a step of obtaining slurry water II by adjusting the pH of the slurry water I obtained in step (I) to 9 to 14. This effectively promotes the replenishment of lithium with respect to the lithium-based polyanion particles (A') contained in the powder (X) in the subsequent step (III).

[0041] The pH of the slurry water II is 9 to 14, preferably 10.5 to 13, and more preferably 11 to 12.5.

[0042] In adjusting the pH in step (II), it is preferable to use one or more pH adjusters selected from sodium hydroxide, potassium hydroxide, sulfuric acid, and hydrochloric acid, and it is more preferable to use one or two pH adjusters selected from sodium hydroxide and sulfuric acid.

[0043] The amount of pH adjuster added may vary depending on the pH of the slurry water I, but it may be any amount that does not leave any undissolved residue. The slurry water II may be stirred before proceeding to the subsequent step (III).

[0044] Step (III) is a step of subjecting the slurry water II obtained in step (II) to a heat treatment for 3 to 5 hours at a temperature of 30° C. or higher but lower than 200° C. Although this is a simple step, it is possible to effectively replenish the lithium that has been released from the lithium-based polyanion particles (A') contained in the powder (X), thereby enabling the regeneration into the desired lithium-based polyanion particles (A).

[0045] The temperature of the heat treatment is 30° C. or higher and lower than 200° C., preferably 30° C. to 180° C., more preferably 50° C. to 180° C., even more preferably 90° C. to 170° C., still more preferably 110° C. to 150° C., and even more preferably 115° C. to 145° C. Furthermore, within this temperature range of 30° C. or higher and lower than 200° C., either a low temperature range of 30° C. or higher and lower than 90° C. or a high temperature range of 90° C. or higher and lower than 200° C. can be selected as appropriate depending on various conditions.

[0046] Specifically, when the temperature of the heat treatment is in the low temperature range of 30°C or higher but lower than 90°C, it may be 30°C to 90°C, or 35°C to 90°C, or even 40°C to 85°C. As described above, when the temperature of the heat treatment in step (III) is in the low temperature range, it is preferable to add the carbon (C) in addition to the powder (X) and the lithium source (Y) in step (I) in order to facilitate effective regeneration of the lithium-based polyanion particles (A'). Furthermore, when the temperature is in such a low temperature range, there is no need to apply pressure.

[0047] On the other hand, when the temperature of the heat treatment is set to a high temperature range of 90°C or higher but lower than 200°C, this high temperature range is also known as a temperature range for hydrothermal reaction treatment, but it may further be 90°C to 180°C, 90°C to 170°C, 110°C to 150°C, or even 115°C to 145°C. When set to such a high temperature range, pressure may be applied using a pressure-resistant container or the like. The pressure is preferably 0.3 MPa to 0.9 MPa, or may be 0.3 MPa to 0.6 MPa.

[0048] The time for the heat treatment is 3 to 5 hours, preferably 3.5 to 4.5 hours, from the viewpoint of facilitating effective regeneration of the lithium-based polyanion particles (A').

[0049] The method of subjecting the material to heat treatment is not particularly limited, and either continuous or batch-type equipment may be used. Heat treatment furnaces such as rotary kiln-type firing furnaces and fixed-bed firing furnaces may also be used, and heat treatment by microwave irradiation may also be performed. Among these, heat treatment by microwave irradiation is preferred from the viewpoint of energy efficiency.

[0050] After the above step (III), the resulting slurry is filtered, washed with water, and then dried to obtain lithium-based polyanion particles that can be used as a positive electrode active material for lithium-ion secondary batteries. Examples of drying methods include freeze-drying and vacuum drying. This process allows for the production of lithium-based polyanion particles (A) that have been regenerated into the lithium-based polyanion particles (A) represented by formula (A) that were originally contained in the positive electrode.

[0051] Since the lithium-based polyanion particles (A) contained in the powder (X) used as one of the raw materials of the present invention are originally supported with carbon, the lithium-based polyanion particles obtained by the present invention also contain supported carbon. Therefore, the lithium-based polyanion particles obtained by the present invention can be used as is as a useful positive electrode material for constructing lithium-ion secondary batteries. Furthermore, when carbon powder (c1) is further mixed as carbon (C) in step (I), the obtained lithium-based polyanion particles can be used as is without recovering the carbon powder (c1), thereby retaining the carbon powder (c1). This makes it possible to prepare a positive electrode slurry and apply it to a current collector without adding a new carbon source when constructing a lithium-ion secondary battery using such lithium-based polyanion particles as a positive electrode material.

[0052] When using the lithium-based polyanionic particles obtained by the present invention as a positive electrode material for a lithium-ion secondary battery, the lithium-based polyanionic particles may be loaded with additional carbon in advance. To load additional carbon onto the obtained lithium-based polyanionic particles, one or more carbon sources selected from cellulose nanofiber-derived carbon and water-soluble carbon material-derived carbon may be added to the slurry water obtained by filtering the slurry obtained after the above step (III). After adding these, the mixture may be spray-dried and calcined to obtain lithium-based polyanionic particles for use as a positive electrode material.

[0053] Furthermore, the method for producing lithium-based polyanionic particles for use as a positive electrode active material in lithium ion secondary batteries of the present invention can be incorporated into a conventional method for producing new lithium-based polyanionic particles (A). That is, the method for producing lithium-based polyanionic particles (A) can be carried out by using the powder (X) as one of the raw materials and going through the steps of the production method of the present invention.

[0054] Specifically, for example, the production method may include the following steps (IX) to (IIIX): (IX) a step of mixing a metal compound including a lithium compound, a manganese compound, and an iron compound, a phosphate compound, a powder (X), a lithium source (Y), and, if necessary, cellulose nanofibers and / or a water-soluble carbon material to obtain slurry water IX; (IIX) a step of adjusting the pH of the obtained slurry water IX to 9 to 14 to obtain slurry water IIX; and (IIIX) a step of subjecting the obtained slurry water IIX to a heat treatment at a temperature of 30°C or higher but lower than 200°C for 3 to 5 hours, and no reducing agent is used.

[0055] The powder (X) and the lithium source (Y) may be the same as those described above, and the lithium compound may be the same as the lithium source (Y). The manganese compound and the iron compound may also be the same as those described above. Furthermore, among the metal compounds, compounds of metals other than the manganese compound and the iron compound (M: M has the same meaning as M in formula (A)) may also be the same as those described above. Steps (IX), (IIX), and (IIIX) may be carried out in accordance with steps (I), (II), and (III), respectively. However, in step (IIIX), it is preferable to subject the raw materials to a heat treatment at a high temperature in order to ensure that the reaction between the raw materials proceeds smoothly.

[0056] This allows for the effective utilization of used lithium ion batteries when producing new lithium-based polyanion particles (A), which will greatly contribute to environmental considerations and as an effective measure against resource depletion.

[0057] The lithium-ion secondary battery can be constructed using the lithium-based polyanion particles obtained by the present invention as a positive electrode material according to a conventional method. Specifically, for example, the obtained lithium-based polyanion particles are kneaded with acetylene black, ketjen black, polyvinylidene fluoride, N-methyl-2-pyrrolidone, or the like to prepare a positive electrode slurry, which is then applied to a current collector and press-molded to form a positive electrode. When carbon powder (c1) is mixed in the above step (I), the obtained lithium-based polyanion particles can be used as is without recovering it, thereby eliminating the need to add acetylene black or ketjen black during the preparation of the positive electrode slurry and simplifying the process.

[0058] The lithium ion secondary battery to which such a positive electrode can be applied is not particularly limited as long as it essentially comprises a positive electrode, a negative electrode, an electrolyte solution, and a separator, or a positive electrode, a negative electrode, and a solid electrolyte.

[0059] The negative electrode is not particularly limited in terms of material composition, and any known material composition can be used as long as it can absorb lithium ions during charging and release them during discharging. For example, lithium metal, graphite, silicon-based materials (Si, SiOx), lithium titanate, or carbon materials such as amorphous carbon can be used. It is preferable to use an electrode formed of an intercalating material capable of electrochemically absorbing and releasing lithium ions, particularly a carbon material. Furthermore, two or more of the above negative electrode materials may be used in combination, such as a combination of graphite and silicon-based materials.

[0060] The electrolyte solution is prepared by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent typically used in electrolyte solutions for lithium ion secondary batteries, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, and oxolane compounds.

[0061] The type of supporting salt is not particularly limited, but LiPF ６ , LiBF ４ , LiClO ４ and LiAsF ６ an inorganic salt selected from the group consisting of: ３ CF ３ , LiC(SO ３ CF ３ ) ２ and LiN(SO ３ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ and LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ) and at least one of the derivatives of said organic salts.

[0062] The separator serves to electrically insulate the positive and negative electrodes and retain the electrolyte, and may be, for example, a porous synthetic resin film, particularly a porous film made of a polyolefin polymer (polyethylene, polypropylene).

[0063] The solid electrolyte electrically insulates the positive and negative electrodes and exhibits high lithium ion conductivity. ０．５１ Li ０．３４ TiO ２．９４ , Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ , Li ７ La ３ Zr ２ O １２ , 50Li ４ SiO ４ ・50Li ３ BO ３ , Li ２．９ P.O. ３．３ N ０．４６ , Li ３．６ Si ０．６ P ０．４ O ４ , Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ , Li １０ GeP ２ S １２ , Li ３．２５ Ge ０．２５ P ０．７５ S ４ , 30Li ２ S・26B ２ S ３ ・44LiI, 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 70Li ２S・30P ２ S ５ , 50Li ２ S・50GeS ２ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Just use

[0064] The shape of the lithium ion secondary battery having the above-described configuration is not particularly limited, and may be various shapes such as a coin shape, a cylindrical shape, a square shape, or an irregular shape enclosed in a laminate outer casing.

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The physical properties of each particle were determined by the following methods and are shown in Table 1.

[0066] <<Crystallite Diameter>> Measurement was performed using an XRD (D8-ADVANCE A-25 model, manufactured by Bruker AXS) with a CuKα target, a tube voltage of 40 kV, a tube current of 40 mA, a scanning range of 10 to 80° (2θ), a step width of 0.0234°, and a scan speed of 0.13° / step. The crystallite diameter (nm) was determined by applying the Scherrer equation to the total angle of the obtained XRD pattern.

[0067] Molar Ratio (Li / P) Using an ICP optical emission spectrometer (ICP-AES PS3520UVDD2, manufactured by Hitachi High-Tech Science Corporation), the molar amounts of Li, Mn, Fe, and P were determined from their respective concentrations by a calibration curve method, and the molar ratio (Li / P) was calculated from the obtained values.

[0068] [Example 1] Particles A-1 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-1 and 20 g of Na ２ S ２ O ８was added to 1 L of water. Then, the mixture was stirred at room temperature for 24 hours, filtered, dried, and then collected to obtain particles A'-1 as lithium-based polyanion particles (A') to be used as powder (X). Next, the Li ＋ The amount of LiOH·H is 1 mol. ２ Particles A'-1 were added to the mixture O and mixed with water to obtain slurry water Ia. Next, the pH of the slurry water Ia was adjusted to 12.5 using NaOH, and the mixture was then placed in an autoclave and subjected to heat treatment at 150°C for 3.5 hours. The pressure inside the autoclave was 0.8 MPa. After the heat treatment, the generated crystals were filtered, dried, and then recovered to obtain particles Z-1 as regenerated lithium-based polyanion particles.

[0069] [Example 2] As the lithium-based polyanion particles (A), particles A-2 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-2 and 15 g of Na ２ S ２ O ８ Particles A'-2 were obtained as lithium-based polyanion particles (A') to be used as powder (X) in the same manner as in Example 1, except that the pH of the slurry water Ia was set to 9, the heat treatment temperature was set to 130°C, and the heat treatment time was set to 4.2 hours. Particles Z-2 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that the pH of the slurry water Ia was set to 9, the heat treatment temperature was set to 130°C, and the heat treatment time was set to 4.2 hours.

[0070] [Example 3] As the lithium-based polyanion particles (A), particles A-3 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-3 and 46 g of Na ２ S ２ O ８ Particles A'-3 were obtained as lithium-based polyanion particles (A') to be used as powder (X) in the same manner as in Example 1, except that LiOH.H ２ Li instead of O２ SO ４ ・H ２ Slurry water Ib was obtained in the same manner as in Example 1, except that O was used. Next, particles Z-3 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that the pH of the obtained slurry water Ib was set to 11.5 and the heat treatment time was set to 4 hours.

[0071] [Example 4] Particles A-4 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-4 and 50 g of Na ２ S ２ O ８ was added to 1 L of water. The mixture was then stirred at room temperature for 24 hours, filtered, dried, and then collected to obtain particles A'-4 as lithium-based polyanion particles (A') to be used as powder (X). ＋ The amount of LiOH·H is 1 mol. ２ Particles A'-4 were added to the mixture O and mixed with water to obtain slurry water Ic. Next, the pH of the slurry water Ic was adjusted to 10.0 using NaOH, and the mixture was then placed in an open container (glass beaker) and subjected to heat treatment at 50°C for 4.5 hours. After the heat treatment, the generated crystals were filtered, dried, and then recovered to obtain particles Z-4 as regenerated lithium-based polyanion particles.

[0072] [Example 5] Particles A-5 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-5 and 50 g of Na ２ S ２ O ８ was added to 1 L of water. Then, the mixture was stirred at room temperature for 24 hours, filtered, dried, and then collected to obtain particles A'-5 as lithium-based polyanion particles (A') to be used as powder (X). Next, the Li ＋ The amount of LiOH·H is 1 mol. ２Particles A'-1 were added to the mixture O and mixed with water to obtain slurry water Id. Next, the pH of the slurry water Id was adjusted to 10.0 using NaOH, and then 15 parts by mass of carbon sheet was added to 100 parts by mass of particles A'-5 to obtain slurry water Id'. The obtained slurry water Id' was placed in an open container (glass beaker) and subjected to heat treatment at 80°C for 4.5 hours. After the heat treatment, the generated crystals were filtered, dried, and the carbon sheet was removed, and then recovered to obtain particles Z-5 as regenerated lithium-based polyanion particles.

[0073] Comparative Example 1 As the lithium-based polyanion particles (A), particles A-6 (LiMn ０．８ Fe ０．２ P.O. ４ , carbon content: 1.2 mass%, crystallite size: 85 nm) and 100 g of particles A-6 and 82 g of Na ２ S ２ O ８ Particles Z-6 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that the above was added to 1 L of water.

[0074] Comparative Example 2 As the lithium-based polyanion particles (A), particles A-7 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-7 and 52 g of Na ２ S ２ O ８ Particles Z-7 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that the above was added to 1 L of water, the pH of the slurry water Ia was adjusted to 11, and the heat treatment time was set to 1 hour.

[0075] Comparative Example 3 As the lithium-based polyanion particles (A), particles A-8 (LiMn ０．８ Fe ０．２ P.O. ４ 100 g of particles A-8 and 80 g of Na ２ S ２ O ８was added to 1 L of water. Then, the mixture was stirred at room temperature for 24 hours, filtered, dried, and then collected to obtain particles A'-8 as lithium-based polyanion particles (A') to be used as powder (X). Next, the Li ＋ The amount of LiOH·H is 1 mol. ２ Particles A'-8 were added to the mixture O and mixed with water to obtain slurry water Ie. Next, the pH of the slurry water Ie was adjusted to 10.0 using NaOH, and then 1.3 parts by mass of Ketjen black was added to 100 parts by mass of particles A'-8 to obtain slurry water Ie'. The obtained slurry water Ie' was placed in an open container (glass beaker) and subjected to heat treatment at 50°C for 4.5 hours. After the heat treatment, the generated crystals were filtered, dried, and then recovered to obtain particles Z-8 as regenerated lithium-based polyanion particles.

[0076] <<Evaluation of Regeneration of Lithium-Based Polyanionic Particles (A') into Lithium-Based Polyanionic Particles (A)>> Using the crystallite diameter values ​​of each regenerated lithium-based polyanionic particle obtained above and the crystallite diameter value of the lithium-based polyanionic particles (A), the crystallite diameter recovery rate (%) was calculated using the following formula (x) and used as an evaluation index. The results are shown in Table 1. The closer this value is to 100%, the better the regeneration performance was. Crystallite diameter recovery rate (%) = {crystallite diameter (nm) of regenerated lithium-based polyanionic particles / crystallite diameter (nm) of lithium-based polyanionic particles (A)} × 100 (x)

[0077]

[0078] <<XRD Pattern Analysis>> Each of the regenerated lithium-based polyanion particles obtained above was measured using an XRD (D8-ADVANCE A-25 model, manufactured by Bruker AXS) with a CuKα target, a tube voltage of 40 kV, a tube current of 40 mA, a scanning range of 10 to 80° (2θ), a step width of 0.0234°, and a scan speed of 0.13° / step to obtain an XRD pattern. The obtained XRD pattern is shown in FIG. 1.

Claims

1. A method for producing lithium-based polyanion particles for use as a positive electrode active material in a lithium ion secondary battery, without using a reducing agent, comprising the following steps (I) to (III): (I) mixing powder (X) containing deteriorated lithium-based polyanion particles (A') obtained from a used lithium ion secondary battery constructed with a positive electrode containing carbon-supported lithium-based polyanion particles (A), and (II) adjusting the pH of the obtained slurry water I to 9 to 14 to obtain slurry water II, and (III) subjecting the obtained slurry water II to a heat treatment at a temperature of 30°C or higher but lower than 200°C for 3 to 5 hours, wherein the lithium-based polyanion particles (A) are represented by the following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ P.O. ４ ...(A) (In formula (A), M represents Mg, Al, Ti, Cu, Zn, Nb, Co, Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd; a, b, c, and x represent numbers that satisfy 0<a≦1.2, 0<b≦1.2, 0<c≦1.2, 0≦x≦0.3, and b+c≠0, and that satisfy a+(valence of Mn)×b+(valence of Fe)×c+(valence of M)×x=3.) 2. A method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium ion secondary batteries, as described in claim 1, wherein the reducing agent is one or more selected from the group consisting of hydrazine, sodium sulfite, sodium thiosulfate, ascorbic acid, and salts thereof.

3. A method for producing lithium-based polyanion particles for use as a positive electrode active material for lithium ion secondary batteries, as described in claim 1 or 2, wherein the molar ratio of Li to P (Li / P) in the deteriorated lithium-based polyanion particles (A') is 0.4 or more and less than 1.

4. A method for producing lithium-based polyanion particles for use as a positive electrode active material for lithium ion secondary batteries according to any one of claims 1 to 3, wherein the temperature of the heat treatment in step (III) is 30°C or higher and 180°C or lower.

5. A method for producing lithium-based polyanion particles for use as a positive electrode active material in lithium ion secondary batteries according to any one of claims 1 to 4, wherein step (I) is a step of obtaining slurry water I by mixing powder (X), lithium source (Y), and carbon (C), and step (III) is a step of subjecting the mixture to a heat treatment at a temperature of 30°C or higher but lower than 90°C.

6. The method for producing lithium-based polyanion particles for use as a positive electrode active material for a lithium ion secondary battery according to claim 5, wherein in step (I), the carbon (C) is carbon powder (c1), and the amount of carbon powder (c1) added is 0.1 to 5 parts by mass per 100 parts by mass of powder (X).

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