Production method of lithium-based polyanion particles for lithium ion secondary battery positive electrode active material

Abstract

To provide a production method of a lithium-based polyanion particle for a positive electrode active material of a lithium ion secondary battery, the method having high safety and enabling simplification of a step as a regeneration process of a used lithium ion battery.SOLUTION: A production method of a lithium-based polyanion particles for a positive electrode active material of a lithium-ion secondary battery is provided. The production method uses a powder (X) including degraded lithium-based polyanion particles (A') obtained from a used lithium-ion secondary battery constructed by a positive electrode containing lithium-based polyanion particles (A) carrying carbon, and the production method comprises: a step (I) in which the powder (X) and a lithium source (Y) are mixed, thereby obtaining slurry water I; a step (II) in which the pH of the obtained slurry water I is adjusted to 9 to 14, thereby obtaining slurry water II; and a step (III) in which the obtained slurry water II is heated at a temperature of 30°C or higher and lower than 200°C for 3 hours to 5 hours, in the steps (I) to (III), reductant is not used. The lithium-based polyanion particles (A) is represented by the formula (A): LiaMnbFecMxPO4, the deteriorated lithium-based polyanion particle (A') is represented by the formula (A) and a mol ratio (Li / P) of Li and P is 0.3 or more and less than 1.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are used in a wide range of applications, including mobile phones, digital cameras, laptop computers, hybrid vehicles, and electric vehicles. x Fe 1-x Lithium-based polyanion particles such as PO4 are highly useful as positive electrode materials for such lithium-ion secondary batteries due to their high safety and large capacity. In recent years, environmental awareness has increased worldwide, and there is a need to address resource depletion. This has led to a strong demand for the recycling of discarded used lithium-ion batteries, and various attempts have been made to regenerate the positive electrode material.

[0003] For example, Non-Patent Document 1 discloses a regeneration process for used LiFePO4 cathode material, in which lithium is replenished under hydrothermal conditions while N2H4·H2O is added as a reducing agent. Patent Document 1 also discloses a selective oxidation-reduction regeneration method for waste lithium iron phosphate, in which lithium and carbon are replenished and the composition is adjusted by primary and secondary sintering under specific conditions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2022-517160 [Non-patent literature]

[0005] [Non-Patent Document 1] 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 Summary of the Invention [Problem to be solved by the invention]

[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 remains unavoidably 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. [Means for solving the problem]

[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 a lithium-ion secondary battery using a 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), The following steps (I) to (III): (I) Mixing powder (X) and lithium source (Y) to obtain slurry water I (II) Adjusting the pH of the obtained slurry water I to 9 - 14 to obtain slurry water II (III) Subjecting the obtained slurry water II to heat treatment at a temperature of 30°C or higher and lower than 200°C for 3 to 5 hours A method for producing lithium - based polyanion particles for a positive electrode active material of a lithium - ion secondary battery, comprising the above steps and without using a reducing agent, The lithium - based polyanion particles (A) are represented by the following formula (A): Li a Mn b Fe c M x PO4···(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 satisfy 0 < a ≤ 1.2, 0 < b ≤ 1.2, 0 < c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and a + (valence of Mn)×b + (valence of Fe)×c + (valence of M)×x = 3. ) and are represented by A method for producing lithium - based polyanion particles for a positive electrode active material of a lithium - ion secondary battery, wherein the deteriorated lithium - based polyanion particles (A’) are represented by the above formula (A) and the molar ratio of Li to P (Li / P) is 0.3 or more and less than 1. It is provided for this purpose.

Effects of the Invention

[0010] According to the method for producing lithium - based polyanion particles for a positive electrode active material of a lithium - ion secondary battery of the present invention, it is a simple and highly safe method without using a reducing agent, and lithium - based polyanion particles having excellent battery physical properties can be obtained, which are highly useful as a positive electrode material for a lithium - ion secondary battery. Therefore, according to the present invention, it is possible to greatly contribute to the realization of recycling of used lithium - ion secondary batteries.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a pattern diagram showing the results of XRD pattern analysis. DETAILED DESCRIPTION OF THE INVENTION

[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 according to the present invention is a production method that uses a powder (X) containing deteriorated lithium-based polyanion particles (A'), which is 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 simply referred to as "lithium-based polyanion particles (A)"). That is, a used lithium ion secondary battery constructed with a positive electrode made using lithium-based polyanion particles (A) as one of its materials gradually loses lithium during use, resulting in a deteriorated state of the positive electrode, and therefore is simply discarded after use. However, the present invention provides a manufacturing method in which the positive electrode of such a used lithium ion secondary battery is subjected to a process such as pulverization to produce powder (X), and this powder (X) containing deteriorated lithium-based polyanion particles (A') is used as one of the raw materials. In other words, the manufacturing method of the present invention for lithium-based polyanion particles for a lithium ion secondary battery positive electrode active material is a manufacturing method for regenerating deteriorated lithium-based polyanion particles (A').

[0013] According to the present invention, for the deteriorated lithium-based polyanion particles (A') contained in the powder (X) (hereinafter, also simply referred to as "lithium-based polyanion particles (A')"), the detached lithium can be effectively replenished, and it can be regenerated into the lithium-based polyanion particles (A) represented by the formula (A) originally contained in the positive electrode (hereinafter, also referred to as "original lithium-based polyanion particles (A)"). Therefore, the lithium-based polyanion particles obtained by the present invention (hereinafter, also referred to as "regenerated lithium-based polyanion particles") can be effectively utilized as a positive electrode material for constructing a lithium-ion secondary battery excellent in battery characteristics again. In addition, the regenerated lithium-based polyanion particles obtained by the present invention are particles regenerated into the lithium-based polyanion particles (A), and are lithium-based polyanion particles represented by the formula (A), similar to the original lithium-based polyanion particles (A). They may have the same composition as the original lithium-based polyanion particles (A), or may have a different composition as long as they are represented by the formula (A). Therefore, for example, for the regenerated lithium-based polyanion particles obtained by the present invention, b, c, etc. in the formula (A) may be appropriately adjusted to desired values.

[0014] Such lithium-based polyanion particles (A) are particles in which carbon is supported and are 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. Li a Mn b Fe c M x PO4···(A) (In the 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 satisfy 0 < a ≤ 1.2, 0 < b ≤ 1.2, 0 < c ≤ 1.2, 0 ≤ x ≤ 0.3, and b + c ≠ 0, and 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 capable of improving 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 PO4, LiMn 0.45 Fe 0.55 PO4, LiMn0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.6 Fe 0.4 PO4, Li 1.2 Mn 0.63 Fe 0.27 PO4 is preferred.

[0017] The crystallite size 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 is a value determined by applying the Scherrer equation to the total angle of the XRD pattern.

[0018] The carbon material forming the carbon supported on the lithium-based polyanion particles (A) is not particularly limited in type, but generally 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 supported on the lithium-based polyanion particles (A) as carbon derived from the cellulose nanofibers or carbon derived from the water-soluble carbon material. Examples of cellulose nanofibers include those with a fiber diameter of 1 nm to 1000 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 lithium-based polyanion particles (A) supported on carbon, and contains deteriorated lithium-based polyanion particles (A'). That is, since the positive electrode constituting the lithium ion secondary battery before use contained 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 lithium-based polyanion particles (A) in a degraded state as lithium-based polyanion particles (A').

[0020] However, in the production method of the present invention, in order to realize a highly useful and effective recycling process to obtain lithium-based polyanionic particles (A), the 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. The molar ratio of Li to P (Li / P) in the lithium-based polyanion 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, from the viewpoint of realizing effective regeneration treatment of lithium-based polyanion particles (A') having a stable crystal structure as the treatment target. The molar ratio of Li to P (Li / P) is calculated from the values ​​determined by performing ICP analysis using an ICP optical emission spectrometer to determine the molar amount of Li and the molar amount of P.

[0021] The crystallite size of the lithium-based polyanion 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. The crystallite diameter means a value determined by applying the Scherrer equation to the full angle of the XRD pattern, similarly to the lithium-based polyanion particles (A).

[0022] The method for obtaining the powder (X) from the recovered used lithium ion secondary batteries is not particularly limited, but for example, the used lithium ion secondary batteries may be disassembled, crushed, roasted, or the like to extract the positive electrodes, which may then be subjected to a process such as pulverization or gravity separation. The powder (X) may be obtained in the form of a slurry water by using water as a suitable 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 polyanion particles (A) as a positive electrode material, the molar ratio of Li to P (Li / P) in powder (X) can be considered to be the same as the molar ratio of Li to P (Li / P) in lithium-based polyanion particles (A'). Therefore, the molar ratio (Li / P) determined by carrying out the above-mentioned ICP analysis using the powder (X) may be used as the molar ratio (Li / P) in the lithium-based polyanion particles (A').

[0024] Specifically, the method for producing lithium-based polyanion particles for use as a positive electrode active material for a lithium ion secondary battery of the present invention includes the following steps (I) to (III): (I) A step of mixing the powder (X) and the lithium source (Y) to obtain slurry water I. (II) A step of adjusting the pH of the obtained slurry water I to 9 to 14 to obtain slurry water II. (III) A step of 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. In other words, since no reducing agent is used, there is no need to consider the toxicity of such a reducing agent, and the process can be effectively simplified while improving safety. Specific examples of such reducing agents include hydrazine, sodium sulfite, sodium thiosulfate, ascorbic acid, and 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 released from the lithium-based polyanion particles (A') contained in the powder (X). Examples of the lithium source (Y) that can be used include hydroxides (e.g., LiOH·H2O, LiOH), sulfates, carbonates, acetates, and nitrates. Among these, hydroxides are preferred. The amount of the lithium source (Y) to be added may vary depending on the composition and amount of the lithium-based polyanionic particles (A'). If necessary, the amount may be adjusted appropriately based on the composition of the lithium-based polyanionic particles represented by formula (A) to be obtained by the present invention, while performing ICP analysis using an ICP emission spectrometer.

[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 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 carbon (C) that can be used 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. 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, from the viewpoint of more effectively regenerating the lithium-based polyanion particles. The average particle size refers to the average value of the particle sizes (length of the major axis) of 100 particles randomly selected in SEM or TEM electron microscope observation. 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, relative to 100 parts by mass of 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 with 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 to 30 parts by mass, more preferably 5 to 25 parts by mass, and even more preferably 10 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, and can be cut to the desired length as needed. It is a carbon material that can be fixed to a reaction vessel or the like when used. 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 is not required during or after the treatment.

[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 shortage of phosphorus, a phosphate compound may also be appropriately added. Examples of manganese compounds that can be used include manganese acetate, manganese nitrate, and manganese sulfate. Examples of iron compounds that can be used include iron acetate, iron nitrate, and iron sulfate. Examples of phosphoric acid compounds that can be used include orthophosphoric acid (H3PO4, phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate.

[0036] In step (I), when the powder (X) and the lithium source (Y) are mixed, there are no particular limitations on the order in which they are added. However, from the viewpoint of more effectively replenishing the separated lithium, it is preferable to add the lithium source (Y) and then add the powder (X). Furthermore, in the case where carbon (C) is further mixed in step (I), the order of addition is not particularly limited, but it is preferable to add the carbon powder (C) after mixing the powder (X) and the lithium source (Y).

[0037] In order to obtain the slurry water I, the powder (X) and the lithium source (Y) are mixed together with water 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 any additional water. It is preferable to pre-stir the slurry water I before proceeding to the next step (II). This can effectively promote the replenishment of lithium. The stirring time is preferably 1 to 60 minutes, more preferably 5 to 30 minutes, and even more preferably 10 to 20 minutes.

[0038] Moreover, 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 the 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] When 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 is sufficient if it is an amount that does not leave any residue undissolved. 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 for 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 heat treatment temperature is in the low temperature range of 30°C or higher and 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 heat treatment is in such a low temperature range, there is no need to apply pressure.

[0047] On the other hand, when the temperature for the heat treatment is in the high temperature range of 90°C or higher but lower than 200°C, which is also known as a hydrothermal reaction treatment, the temperature may be 90°C to 180°C, 90°C to 170°C, 110°C to 150°C, or even 115°C to 145°C. Furthermore, when the temperature is to be in such a high temperature range, pressure may be applied using a pressure-resistant container, etc. The pressure is preferably 0.3 MPa to 0.9 MPa, and 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 step (III), the obtained 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 makes it possible to obtain 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] 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, and therefore 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 they are 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 allowing the carbon powder (c1) to remain present. This makes it possible to prepare a positive electrode slurry and coat it on 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 beforehand. 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 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 polyanion 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 polyanion particles (A). That is, the method for producing lithium-based polyanion 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 following steps (IX) to (IIIX): (IX) A step of obtaining slurry water IX by mixing metal compounds including lithium compounds, manganese compounds, and iron compounds, a phosphate compound, powder (X), a lithium source (Y), and, if necessary, cellulose nanofibers and / or a water-soluble carbon material. (IIX) A step of adjusting the pH of the obtained slurry water IX to 9 to 14 to obtain slurry water IIX. (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 a manufacturing method that does not use a reducing agent.

[0055] The powder (X) and the lithium source (Y) may be the same as those described above, the lithium compound may be the same as the lithium source (Y), and the manganese compound and the iron compound may 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 be the same as those described above. Steps (IX), (IIX), and (IIIX) may be carried out in accordance with the above-mentioned steps (I), (II), and (III), respectively, except that step (IIIX) is preferably a step of subjecting the raw materials to a heat treatment in a high temperature range in order to ensure that the reaction of the raw materials proceeds smoothly.

[0056] This allows for the effective use 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 mixed 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, thereby 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 supporting salt is not particularly limited in type, but is preferably at least one of inorganic salts selected from LiPF6, LiBF4, LiClO4, and LiAsF6, derivatives of these inorganic salts, organic salts selected from LiSO3CF3, LiC(SO3CF3)2, LiN(SO3CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9), and derivatives of these organic salts.

[0062] The separator serves to electrically insulate the positive and negative electrodes and retain the electrolyte solution, and may be, for example, a porous synthetic resin film, particularly a porous film 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 (PO4)3, Li7La3Zr2O 12 , 50Li4SiO4·50Li3BO3, Li 2.9 PO 3.3 N 0.46 , Li 3.6 Si 0.6 P 0.4 O4, Li 1.07 Al 0.69 Ti 1.46 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75S4, 30Li2S 26B2S3 44LiI, 63Li2S 36SiS2 1Li3PO4, 57Li2S 38SiS2 5Li4SiO4, 70Li2S 30P2S5, 50Li2S 50GeS2, Li7P3S 11 , Li 3.25 P 0.95 Just use S4.

[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. [Example]

[0065] The present invention will be specifically described below based on 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> Measurements were 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 calculated by applying the Scherrer equation to the total angle of the obtained XRD pattern.

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

[0068] [Example 1] As the lithium-based polyanion particles (A), particles A-1 (LiMn 0.8 Fe 0.2PO4, carbon content: 1.2 mass%, crystallite diameter: 121.1 nm) was used, and 100 g of particles A-1 and 20 g of Na2S2O8 were added to 1 L of water. Next, after stirring at room temperature for 24 hours, the mixture was filtered, dried, and then collected to obtain particles A'-1 as lithium-based polyanion particles (A') to be used as powder (X). Next, Li of particle A'-1 + Particles A'-1 were added to LiOH·HO in an amount sufficient to give 1 mole of Particle A'-1, and mixed with water to obtain slurry water Ia. The pH of the slurry water Ia was then adjusted to 12.5 using NaOH, after which it was placed in an autoclave and heated at 150°C for 3.5 hours. The pressure inside the autoclave was 0.8 MPa. After the heat treatment, the produced crystals were filtered, dried, and then collected 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 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 100 g of particles A-2 and 15 g of Na2S2O8 were added to 1 L of water using a polyanion powder (X) containing 1.2% Na2SO4, carbon content: 1.2 mass%, crystallite diameter: 180.4 nm. Next, 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 9, the heat treatment temperature was 130°C, and the heat treatment time was 4.2 hours.

[0070] [Example 3] As the lithium-based polyanion particles (A), particles A-3 (LiMn 0.8 Fe 0.2 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 100 g of particles A-3 and 46 g of Na2S2O8 were added to 1 L of water using a polyanion powder (X) containing 1.2% Na2SO4, carbon content: 1.2 mass%, crystallite diameter: 106.8 nm. Next, slurry water Ib was obtained in the same manner as in Example 1, except that LiSO·H0 was used instead of LiOH·H0. 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] As the lithium-based polyanion particles (A), particles A-4 (LiMn 0.8 Fe 0.2 PO4, carbon content: 1.2 mass%, crystallite diameter: 89 nm) was used, and 100 g of particles A-4 and 50 g of Na2S2O8 were added to 1 L of water. Next, after stirring at room temperature for 24 hours, the mixture was filtered, dried, and then collected to obtain particles A'-4 as lithium-based polyanion particles (A') to be used as powder (X). Next, Li of particle A'-4 + Particles A'-4 were added to LiOH·H2O in an amount sufficient to give 1 mol of the granules, and the mixture was mixed with water to obtain slurry water Ic. The pH of the slurry water Ic was then adjusted to 10.0 using NaOH, and the slurry water Ic was then placed in an open container (glass beaker) and heated at 50°C for 4.5 hours. After the heat treatment, the produced crystals were filtered, dried, and then collected to obtain particles Z-4 as regenerated lithium-based polyanion particles.

[0072] [Example 5] As the lithium-based polyanion particles (A), particles A-5 (LiMn 0.8 Fe 0.2 PO4, carbon content: 1.2 mass%, crystallite diameter: 87.3 nm) was used, and 100 g of particles A-5 and 50 g of Na2S2O8 were added to 1 L of water. Next, after stirring at room temperature for 24 hours, the mixture was filtered, dried, and then collected to obtain particles A'-5 as lithium-based polyanion particles (A') to be used as powder (X). Next, Li of particle A'-5 +Particles A'-1 were added to LiOH·HO in an amount sufficient to give 1 mole of Particle A'-1, and the mixture was mixed with water to obtain slurry water Id. The pH of the slurry water Id was then adjusted to 10.0 using NaOH, and 15 parts by mass of carbon sheet was added to 100 parts by mass of particles A'-5 to obtain slurry water Id'. The resulting slurry water Id' was placed in an open container (glass beaker) and heated at 80°C for 4.5 hours. After the heat treatment, the generated crystals were filtered, dried to remove the carbon sheet, and then collected 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 Particles Z-6 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that 100 g of particles A-6 and 82 g of Na2S2O8 were 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 Particles Z-7 were obtained as regenerated lithium-based polyanion particles in the same manner as in Example 1, except that 100 g of particles A-7 and 52 g of Na2S2O8 were 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 0.2PO4, carbon content: 1.2 mass%, crystallite diameter: 155.1 nm) was used, and 100 g of particles A-8 and 80 g of Na2S2O8 were added to 1 L of water. Next, after stirring at room temperature for 24 hours, the mixture was filtered, dried, and then collected to obtain particles A'-8 as lithium-based polyanion particles (A') to be used as powder (X). Next, Li of particle A'-8 + Particles A'-8 were added to LiOH·HO in an amount sufficient to give 1 mole of LiOH, and the mixture was mixed with water to obtain slurry water Ie. The pH of the slurry water Ie was then adjusted to 10.0 using NaOH, and 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 resulting slurry water Ie' was placed in an open container (glass beaker) and heated at 50°C for 4.5 hours. After the heat treatment, the resulting crystals were filtered, dried, and then collected to obtain particles Z-8 as regenerated lithium-based polyanion particles.

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

[0077] [Table 1]

[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 resulting XRD pattern is shown in FIG.

Claims

1. A 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), The following steps (I) to (III): (I) A step of mixing the powder (X) and the lithium source (Y) to obtain slurry water I. (II) A step of adjusting the pH of the obtained slurry water I to 9 to 14 to obtain slurry water II. (III) A step of 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. A method for producing lithium-based polyanion particles for a positive electrode active material of a lithium ion secondary battery, which comprises the steps of: The lithium-based polyanion particles (A) are represented by the following formula (A): Li ａ Mn ｂ Fe ｃ M ｘ 2O 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.) is expressed as A method for producing lithium-based polyanion particles for use as a positive electrode active material for a lithium ion secondary battery, wherein the deteriorated lithium-based polyanion particles (A') are represented by the above formula (A) and have a molar ratio of Li to P (Li / P) of 0.3 or more and less than 1.

2. 2. 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 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. 3. A method for producing lithium-based polyanion particles for use as a positive electrode active material for a lithium ion secondary battery according to 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. 3. 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 1, wherein the temperature of the heat treatment in step (III) is 30°C or higher and 180°C or lower.

5. The step (I) is a step of obtaining slurry water I by mixing powder (X), a lithium source (Y), and carbon (C), and 3. 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 1, wherein step (III) is a step of subjecting the particles to a heat treatment at a temperature of 30°C or higher but lower than 90°C.

6. 6. The method for producing lithium-based polyanion particles for a positive electrode active material of 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 parts by mass to 5 parts by mass per 100 parts by mass of the powder (X).

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