Method for reproducing negative electrode active material

Abstract

The present invention relates to a method for reproducing a negative electrode active material having improved rapid charge / discharge characteristics from a used lithium ion secondary battery. The technique disclosed herein is a method for reproducing a negative electrode active material from a used lithium ion secondary battery, the method including: a preparation step S10 for preparing a used lithium ion secondary battery 1 including a positive electrode 30, a negative electrode 40 provided with a negative electrode active material including a carbon material, and an electrolyte solution; a charging step (S20) in which the lithium ion secondary battery (1) is charged; a discharge step (S30) for discharging the lithium ion secondary battery (1) after the charge step (S20) at a discharge rate higher than the charge rate of the charge step (S20); and a recovery step (S40) in which, for the lithium ion secondary battery (1) after the discharge step (S30), the negative electrode active material containing the carbon material is recovered from the negative electrode (40).

Description

Technical Field

[0001] The present disclosure relates to a method for reproducing a negative electrode active material. Background Art

[0002] Secondary batteries are suitably used in various applications, including driving power sources mounted on hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), and the demand for them is rapidly expanding. In response to this demand, the demand for technologies related to the reproduction of negative electrode active materials from used lithium-ion secondary batteries is also rising. As a technology related to the reproduction of negative electrode active materials, for example, the following technology is disclosed in Japanese Patent Publication No. 2006-228509: the negative electrode is taken out of the lithium-ion secondary battery, the negative electrode is washed with a liquid containing water, and the negative electrode is separated into a negative electrode composite material containing a negative electrode active material and a binder and a current collector substrate, and then the negative electrode composite material is mixed in a solvent that can dissolve or disperse the binder to prepare a negative electrode paste, which is applied to the negative electrode collector.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Publication No. 2006-228509 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the negative electrode active material, not only the technology related to the reproduction of the negative electrode active material is required, but also the performance improvement of the reproduced negative electrode active material, such as the improvement of the rapid charge and discharge characteristics, is required. In the negative electrode active material recovered by the prior art disclosed in Patent Document 1, the rapid charge and discharge characteristics are not considered. Therefore, the above-mentioned requirements for rapid charge and discharge characteristics cannot be fully met.

[0008] The technology disclosed herein has been accomplished in view of the above-mentioned actual situation, and relates to a method for reproducing a negative electrode active material having improved rapid charge and discharge characteristics from a used lithium-ion secondary battery.

[0009] Means for solving problems

[0010] The technology disclosed herein is a method for reproducing negative electrode active materials from used lithium-ion secondary batteries, comprising: a preparation step, in which a used lithium-ion secondary battery including a positive electrode, a negative electrode having a negative electrode active material containing a carbon material, and an electrolyte is prepared; a charging step, in which the lithium-ion secondary battery is charged; a discharging step, which is a step of discharging the lithium-ion secondary battery after the charging step, wherein the discharge is performed at a discharge rate higher than the charging rate of the charging step; and a recovery step, in which, for the lithium-ion secondary battery after the discharging step, the negative electrode active material containing the carbon material is recovered from the negative electrode.

[0011] According to this configuration, by discharging the lithium ion secondary battery at a discharge rate higher than the charge rate, the surface layer of the negative electrode active material of the negative electrode is amorphized, and the rapid charge and discharge characteristics of the negative electrode active material are improved. Therefore, the negative electrode active material with improved rapid charge and discharge characteristics can be reproduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a longitudinal cross-sectional view schematically showing the internal structure of a lithium ion secondary battery according to one embodiment.

[0013] Figure 2 To illustrate Figure 1 A perspective view of an electrode body of a lithium-ion secondary battery shown.

[0014] Figure 3 A flowchart for explaining a reproduction method according to one embodiment.

[0015] Figure 4 This is a flow chart for explaining a sub-process of a recovery process according to one embodiment.

[0016] Figure 5 This is a partially enlarged view schematically showing the appearance of the surface layer of the negative electrode active material (carbon material) and lithium ions according to one embodiment.

[0017] Description of Reference Numerals

[0018] 1Lithium-ion secondary battery

[0019] 10 Shell

[0020] 12 Positive terminal

[0021] 14 Negative terminal

[0022] 16 injection holes

[0023] 18 Sealing member

[0024] 20 electrode body

[0025] 30 positive electrode

[0026] 32 positive electrode core

[0027] 34 Positive electrode active material layer

[0028] 40 negative electrode

[0029] 42 negative electrode core

[0030] 44 Negative electrode active material layer

[0031] 46 Negative electrode active material

[0032] 50 separators

[0033] 60 Lithium Ion

[0034] 62 solvent molecules DETAILED DESCRIPTION

[0035] The following is a description of the embodiments of the technology disclosed herein with reference to the accompanying drawings. It should be noted that matters other than those specifically mentioned in this specification, i.e., matters required for the implementation of the technology disclosed herein, can be understood as design matters for those skilled in the art based on the prior art in the field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the field.

[0036] It should be noted that in the following drawings, the same figure marks are marked for components and parts that play the same role, and repeated descriptions are sometimes omitted or simplified. In addition, the expression "A~B" indicating the range in this specification means above A and below B, and also includes the meanings of "preferably greater than A" and "preferably less than B". It should be noted that in this specification, "secondary battery" refers to a storage device that can be repeatedly charged and discharged, and is a term that includes storage elements such as so-called storage batteries and double-layer capacitors. In addition, the so-called "lithium ion secondary battery" in this specification refers to a secondary battery that uses lithium ions as charge carriers and realizes charging and discharging by the movement of charges accompanied by lithium ions between positive and negative electrodes.

[0037] 1. Prepare the Object

[0038] In the method for reproducing the negative electrode active material according to the present embodiment, a predetermined lithium ion secondary battery is prepared to reproduce the negative electrode active material. As an example of the preparation object here, a used lithium ion secondary battery can be cited. The lithium ion secondary battery is specifically described below. Figure 1 It is a longitudinal cross-sectional view schematically showing the internal structure of a lithium-ion secondary battery. Figure 2 To illustrate Figure 1 A three-dimensional diagram of an electrode body of a lithium-ion secondary battery is shown. Figure 1As shown, the lithium ion secondary battery 1 includes a case 10 , an electrode body 20 , and an electrolyte (not shown).

[0039] (1) Housing

[0040] The shell 10 is a box-shaped container. The electrode body 20 and the electrolyte are accommodated inside the shell 10. For the shell 10, for example, a metal material (aluminum (Al) or the like) having a certain strength is used. An injection hole 16 may be provided in the shell 10. The injection hole 16 is a hole for injecting the electrolyte. After the electrolyte is injected, the injection hole 16 is sealed with a sealing member 18. In addition, a positive terminal 12 and a negative terminal 14 are installed in the shell 10. The positive terminal 12 and the negative terminal 14 are connected to the electrode body 20 inside the shell 10. Specifically, the positive terminal 12 and the positive electrode 30 of the electrode body 20 (see Figure 2 ) is connected. Aluminum (Al) or the like is used for the positive electrode terminal 12. On the other hand, the negative electrode terminal 14 is connected to the negative electrode 40 of the electrode body 20. Copper (Cu) or the like is used for the negative electrode terminal 14.

[0041] (2) Electrode body

[0042] The electrode body 20 is a power generation element of the lithium ion secondary battery 1. Figure 2 As shown, the electrode body 20 includes a positive electrode 30, a negative electrode 40 and a separator 50. Figure 2 The electrode body 20 shown is a wound electrode body. The wound electrode body is made by stacking a positive electrode 30, a negative electrode 40, and a separator 50 to form a long strip-shaped stack, and winding the stack. However, the structure of the electrode body 20 is not particularly limited, and may be other structures known in the art (stacked electrode body, etc.).

[0043] The positive electrode 30 includes: a positive electrode core 32 which is a conductive metal foil, and a positive electrode active material layer 34 applied on the surface of the positive electrode core 32. Aluminum (Al) or the like is used for the positive electrode core 32. In addition, the positive electrode active material layer 34 is a composite layer containing a positive electrode active material, a conductive material, a binder, and the like. The positive electrode active material is a particulate material that can reversibly absorb and release charge carriers. Examples of the positive electrode active material include lithium nickel composite oxides (such as LiNiO2, etc.), lithium cobalt composite oxides (such as LiCoO2, etc.), lithium nickel cobalt manganese composite oxides (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc.), lithium nickel cobalt aluminum composite oxides (such as LiNi 0.8 Co 0.15 Al 0.5 O2, etc.), lithium manganese composite oxides (such as LiMn2O4, etc.), lithium nickel manganese composite oxides (such as LiNi0.5 Mn 1.5 Lithium transition metal composite oxides such as LiO4, etc.; lithium transition metal phosphorus oxides (such as LiFePO4, etc.). In addition, as conductive materials, carbon materials such as acetylene black and graphite can be listed. In addition, as binders, resin materials such as polyvinylidene fluoride (PVDF) can be listed.

[0044] The negative electrode 40 includes: a negative electrode core 42 which is a conductive metal foil, and a negative electrode active material layer 44 provided on the surface of the negative electrode core 42. For the negative electrode core 42, copper (Cu) or the like is used. In addition, the negative electrode active material layer 44 is a composite layer containing a negative electrode active material, a binder, a thickener, etc. The negative electrode active material is a particulate material that can reversibly absorb and release charge carriers. The negative electrode active material to be prepared must contain a carbon material. As the carbon material, for example, graphite, hard carbon, soft carbon, etc. can be listed, among which graphite is preferably used. The graphite can be natural graphite or artificial graphite. In addition, as the negative electrode active material, as long as it does not significantly impair the effect of the present technology, in addition to the above-mentioned carbon materials, lithium titanate (LTO), silicon carbide, a composite containing carbon and silicon (Si-C composite), silicon oxide (SiO X ) etc. There is no particular limitation, but from the viewpoint of reproduction efficiency, the ratio of carbon material is preferably 50% by mass or more when the negative electrode active material as a whole is 100% by mass. As a binder, resin materials such as styrene butadiene rubber (SBR) can be cited. As a thickener, resin materials such as carboxymethyl cellulose (CMC) can be cited.

[0045] In several preferred schemes, the positive and negative electrode capacity ratio of the lithium ion secondary battery 1 is preferably greater than 1.0. As a result, it is possible to more preferably reproduce negative electrode active materials with excellent rapid charge and discharge performance. The positive and negative electrode capacity ratio is preferably greater than 1.5, more preferably greater than 1.2, more preferably greater than 1.05, and further preferably greater than 1.0. If the positive and negative electrode capacity ratio is closer to 1.0, the utilization rate of the negative electrode active material is improved, so that the surface of the negative electrode active material can be suitably amorphized to obtain a negative electrode active material with excellent rapid charge and discharge performance. In addition, if the positive and negative electrode capacity ratio is lower than 1.0 (less than 1.0), metallic lithium is precipitated on the negative electrode, and short circuit may occur, so the positive and negative electrode capacity ratio is preferably greater than 1.0. There is no particular limitation on the upper limit of the positive and negative electrode capacity ratio, preferably less than 2.2, more preferably less than 2.0, more preferably less than 1.9, and further preferably less than 1.7. Furthermore, in this specification, the so-called "positive and negative electrode capacity ratio" can be obtained by respectively calculating the positive electrode capacity and the negative electrode capacity, and can be obtained by the following formula: Positive and negative electrode capacity ratio = negative electrode capacity / positive electrode capacity. Among them, the positive and negative electrode capacity ratio can be easily adjusted by, for example, changing the unit area mass of the positive and negative electrodes, changing the type of positive and negative electrode active materials. It should be noted that the so-called "unit area mass" refers to the value obtained by dividing the mass of the electrode active material layer by the area of ​​the formation area (mass of the electrode active material layer / area of ​​the formation area). In addition, the positive electrode capacity can be obtained by making, for example, a half-cell unit with Li metal as the counter electrode, as the capacity when initially charged in a voltage range corresponding to the half-cell unit (for example, about 2 to 4.2V) (that is, the initial positive electrode charge capacity). Moreover, the negative electrode capacity can be obtained by, for example, adding up the initial negative electrode discharge capacity and the operating voltage range of the negative electrode.

[0046] In addition, the separator 50 is an insulating sheet between the positive electrode 30 and the negative electrode 40. For the separator 50, for example, a resin material such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. is used. In addition, a heat-resistant layer containing an inorganic filler can be formed on the surface of the separator 50. Examples of the inorganic filler include inorganic oxides such as aluminum oxide, magnesium oxide, silicon oxide, and titanium oxide, nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, mica, talc, boehmite, zeolite, apatite, and clay minerals such as kaolin.

[0047] (3) Electrolyte

[0048] The electrolyte is present between the positive electrode 30 and the negative electrode 40. Thus, the charge carrier can be moved between the positive electrode 30 and the negative electrode 40. As an example of the electrolyte, non-aqueous electrolytes, gel electrolytes, etc. can be listed. Furthermore, the electrolyte can use the electrolyte that can be used in the previous lithium ion secondary battery without particular restrictions. The electrolyte typically contains a solvent and a supporting salt. As a solvent, various non-aqueous solvents used in such lithium ion secondary batteries are used, such as carbonate-based non-aqueous solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). As a supporting salt, for example, lithium salts such as LiPF6, LiBF4, and bis(fluorosulfonyl)imide lithium (LiFSI) can be preferably used. The concentration of the supporting salt is not particularly limited, preferably 0.7 mol / L or more and 1.3 mol / L or less. Furthermore, the electrolyte may contain components other than the above-mentioned solvent and supporting salt, for example, various additives such as a gas generator, a film forming agent, a dispersant, and a thickener, as long as the effect of the present technology is not significantly impaired. As additives for the non-aqueous electrolyte 80, for example, positive and negative electrode film forming agents such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sultone (PS); overcharge prevention agents such as biphenyl (BP), cyclohexylbenzene (CHB), tert-butylbenzene, and tert-amylbenzene can be listed.

[0049] As an example of the preparation object in the reproduction method involved in this embodiment, the lithium ion secondary battery 1 is described above. However, the reproduction method disclosed herein is not limited to the method with the lithium ion secondary battery 1 as the preparation object of the above-mentioned structure. That is, the lithium ion secondary battery of the preparation object of the reproduction method disclosed herein only needs to include a positive electrode, a negative electrode and an electrolyte, and is not particularly limited to a specific structure.

[0050] 2. Reproduction method of negative electrode active material

[0051] Hereinafter, the method for reproducing the negative electrode active material according to the present embodiment will be described. Figure 3 A flowchart for explaining a reproduction method according to one embodiment. Figure 4 This is a flowchart for explaining the sub-processes of the recovery process S40 according to one embodiment.

[0052] like Figure 3 As shown, the negative electrode active material reproduction method according to the first embodiment includes: a preparation step S10, a charging step S20, a discharging step S30, and a recovery step S40. In addition, the reproduction method disclosed herein may further include other steps at any stage, and the other processes may be the same as before. Each step is described below.

[0053] (1) Preparation step S10

[0054] In the preparation step S10, a lithium ion secondary battery for reproducing the negative electrode active material is prepared. The lithium ion secondary battery prepared here includes: a positive electrode, a negative electrode including a negative electrode active material including a carbon material, and an electrolyte. In addition, the details of the lithium ion secondary battery have been described, so repeated description is omitted.

[0055] (2) Charging step S20

[0056] In the charging step S20, the lithium ion secondary battery prepared in the preparation step S10 is charged. The characteristic is that in the charging step S20, the lithium ion secondary battery is charged at a charging rate relatively lower than the discharge rate in the discharge step S30.

[0057] In several preferred schemes, the charging step S20 is preferably performed at a charging rate of 0.5C or less. In this way, a negative electrode active material with excellent rapid charge and discharge performance can be reproduced. The charging rate of the charging step S20 is preferably 0.5C or less, more preferably 0.3C or less, and further preferably 0.2C or less. There is no particular limitation on the charging rate of the charging step S20, for example, it is 0.01C or more, preferably 0.1C or more.

[0058] In several preferred schemes, in the charging process S20, it is preferred to charge until the state of charge (SOC; State of Charge) of the lithium ion secondary battery 1 becomes 50% or more. Thereby, a negative electrode active material with excellent rapid charge and discharge performance can be reproduced. In addition, it is more preferred to charge until the SOC of the lithium ion secondary battery 1 becomes 80% or more, and it is further preferred to charge until it becomes 100% (rated voltage). The higher the SOC in the charging process S20, the wider the lithium ions diffuse in the layer of the negative electrode active material, so the surface of the negative electrode active material can be more suitably amorphized. That is, a negative electrode active material with excellent rapid charge and discharge performance can be suitably reproduced. In addition, charging can be once, for example, it can also be repeated more than twice with discharge.

[0059] The temperature during the charging step S20 is not particularly limited, and is, for example, 100° C. or less, preferably 80° C. or less. The temperature during the charging step S20 is not particularly limited, and is, for example, 0° C. or more, preferably 40° C. or more, and more preferably 50° C. or more.

[0060] (3) Discharging step S30

[0061] In the discharge step S30, the lithium ion secondary battery that has passed through the charging step S20 is discharged. The discharge step S30 is characterized in that the lithium ion secondary battery is discharged at a discharge rate higher than the charge rate in the charging step S20.

[0062] Figure 5 This is a partially enlarged view schematically showing the surface layer of the negative electrode active material 46 and the appearance of lithium ions 60 according to one embodiment. Figure 5 (A) is the state before the charging step S20 is performed. Figure 5 (B) and Figure 5 (C) is the state in the charging step S20. Figure 5 (D) is a state in the discharge step S30. Figure 5 In (B) to (D), for convenience of explanation, the behavior of lithium ions 60 is indicated by white arrows.

[0063] exist Figure 5 In the embodiment, the negative electrode active material 46 is a carbon material. Before the charging step S20 is performed, the lithium ions 60 are typically stabilized in a coordinated state (solvation) of the solvent molecules 62 constituting the electrolyte (see Figure 5 (A)). Among them, Figure 5 As shown in (B), for the lithium ion secondary battery 1, the charging step S20 is performed, so that the lithium ions 60 in the electrolyte are inserted into the interlayer of the surface layer of the negative electrode active material 46. The inserted lithium ions 60 are as follows Figure 5 As shown in (C), as the charging step S20 is performed, the solvent molecules 62 are removed (desolvated) and diffused in the layer of the negative electrode active material 46. As a result, the interlayer of the negative electrode active material 46 is expanded. In addition, by making the discharge rate relatively higher than the charge rate of the charging step S20, the discharge step S30 is performed, so that the lithium ions 60 inserted into the interlayer of the negative electrode active material 46 are as follows. Figure 5 (D) shows that the lithium ions 60 are again released to the outside of the negative electrode active material 46. By the charging step S20 and the discharging step S30, the surface layer of the negative electrode active material 46 in which the lithium ions 60 are inserted and released is amorphous (refer to Figure 5 (D)). The surface layer of the negative electrode active material 46 is amorphized, thereby improving the rapid charge and discharge performance of the negative electrode active material 46. Then, the negative electrode active material 46 with improved rapid charge and discharge performance can be recovered by the recovery step S40 described later.

[0064] In several preferred schemes, the discharge step S30 is preferably performed at a discharge rate of 0.5C or more. The discharge rate of the discharge step S30 is preferably 0.5C or more, more preferably 0.8C or more, and further preferably 1.0C or more. Thus, a negative electrode active material with excellent rapid charge and discharge performance can be reproduced. The discharge rate of the discharge step S30 is not particularly limited, and is 20C or less, preferably 10C or less.

[0065] In some preferred embodiments, in the discharge step S30, it is preferred to discharge until the state of charge (SOC: State of Charge) of the lithium ion secondary battery 1 becomes 30% or less. In addition, it is more preferred to discharge until the SOC of the lithium ion secondary battery 1 becomes 20% or less, more preferably 10% or less, more preferably 5% or less, and further preferably to discharge until it becomes 0%. In addition, the discharge may be performed once, or it may be repeated twice or more, for example, with charging in between.

[0066] The difference between the discharge rate and the charge rate (discharge rate - charge rate) is preferably 0.4C or more, more preferably 0.7C or more, preferably 0.8C or more, preferably 0.9C or more, and more preferably 3.9C or more. The greater the difference between the discharge rate and the charge rate, the more suitable it is to amorphize the surface of the negative electrode active material. Therefore, it is possible to reproduce a negative electrode active material with excellent rapid charge and discharge performance. There is no particular limitation on the upper limit of the difference between the discharge rate and the charge rate (discharge rate - charge rate), for example, it may be less than 10C.

[0067] (4) Recovery process S40

[0068] In the recycling step S40, the negative electrode active material is recycled from the lithium ion secondary battery that has undergone the charging step S20 and the discharging step S30. The recycling method of the negative electrode active material involved in the recycling step S40 can use a conventionally known technique and is not particularly limited. The recycling step S40 is, for example, Figure 4 As shown, as sub-steps, a calcination step S41, a screening step S43, an acid treatment step S45, and a magnetic screening step S47 may be provided. These steps will be described in detail below.

[0069] (4-1) Calcination Step S41

[0070] In the roasting process S41, the lithium-ion secondary battery is roasted at a predetermined temperature. Thus, the liquid component (electrolyte, etc.) in the recycling object can be removed, and the resin component (adhesive, separator, etc.) can be carbonized. In addition, by implementing the roasting process S41, the function as a battery can be stopped. For the method of the roasting process S41, the technology used in the previous recycling technology can be used without particular restrictions, and since it is not a feature of the technology disclosed herein, a detailed description is omitted.

[0071] (4-2) Screening step S43

[0072] In the screening step S43, each component included in the lithium ion secondary battery 1 is screened. The screening step S43 may be performed by a conventionally known method, such as screening using a sieve or visual inspection.

[0073] Furthermore, in the screening step S43, the lithium-ion secondary battery 1 may be crushed as needed. Thus, the crushed lithium-ion secondary battery 1 can be obtained, and the efficiency of screening each component can be improved. For example, when the lithium-ion secondary battery 1 is a recycling object, it is preferable to crush the shell 10 and the electrode body 20. Thus, it is easy to remove the shell 10, the negative electrode core 42 and the positive electrode 30 from the lithium-ion secondary battery 1.

[0074] Although not limited to this, the crushed lithium ion secondary battery 1 obtained by the above crushing process is screened using a sieve. In this case, typically, on the sieve, metal components (Al, Cu, etc.) mainly from the shell 10, the positive electrode core 32, and the negative electrode core 42 remain as coarse particles, and under the sieve, black lumps are obtained as fine particles from which the metal components (Al, Cu, etc.) are substantially removed. The black lumps typically contain negative electrode active materials and positive electrode active materials (such as Ni, Co, etc.).

[0075] In addition, in the screening step S43, the screened black agglomerates can be further screened using a flotation separation method. In this way, components other than the negative electrode active material (such as Ni, Co, etc.) in the black agglomerates can be substantially removed. As for the flotation separation method, well-known techniques such as multi-oil flotation, water surface flotation, and foam flotation can be used without particular limitation.

[0076] (4-3) Acid Treatment Step S45

[0077] In the acid treatment step S45, the black agglomerates obtained in the screening step S43 are mixed with an acidic solution. As a result, the metal elements (Al, Cu, Ni, Co, etc.) in the black agglomerates are dissolved in the acidic solution, while the negative electrode active material is not dissolved in the acidic solution and remains as a residue. In addition, depending on the composition of the recovery object, the composition of the acidic solution, etc., some of the metal elements (Fe, etc.) in the black agglomerates are sometimes not dissolved in the acidic solution and remain as a residue. That is, the residue obtained in the acid treatment step S45 may contain, for example, Fe, etc. in addition to the negative electrode active material. In this case, for the metal elements in the residue, for example, the magnetic screening step S47 described later can be used to remove. As for the steps of the acid treatment step S45, the steps known in the past can be used without particular restrictions. As an example, the pH of the acidic solution used in the acid treatment step S45 is preferably -1.5 to 1.5 (more preferably -0.5 to 0.5). As a result, the metal components in the black agglomerates can be appropriately dissolved. In addition, specific examples of the acidic solution include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid, and organic acids such as citric acid, ascorbic acid, oxalic acid, and acetic acid. In addition, the present invention is not limited thereto, and in the acid treatment step S45, a reducing agent such as hydrogen peroxide can be added in addition to the acidic solution. Thus, the metal elements in the black mass are suitably dissolved in the acidic solution, and the treatment time of the acid treatment step S45 can be shortened.

[0078] The acidic solution and the residue after the acid treatment step S45 are subjected to solid-liquid separation by filtering or the like, thereby obtaining the residue containing the negative electrode active material. As for the method of solid-liquid separation, conventionally known means can be adopted without particular limitation. Furthermore, the acidic solution after solid-liquid separation is not limited thereto, and for example, the metal elements (Ni, Co, etc.) in the acidic solution can be recovered by conventionally known treatment methods.

[0079] (4-4) Magnetic screening step S47

[0080] In the magnetic screening step S47, the residue obtained in the acid treatment step S45 is screened by magnetic force. Thus, the negative electrode active material and the magnetized material (metal component) as non-magnetized materials in the residue can be screened. That is, the negative electrode active material involved in the present embodiment can be obtained by using the magnetic screening step S47. The magnetic screening step S47 can adopt the conventionally known steps without particular limitation.

[0081] The above is a description of the reproduction method of the negative electrode active material involved in the present embodiment. According to the reproduction method involved in the present embodiment including the preparation step S10, the charging step S20, the discharging step S30 and the recovery step S40 as described above, a negative electrode active material that amorphizes the surface of the negative electrode active material (hereinafter referred to as the "active material substrate") as the preparation object can be obtained. Therefore, according to the reproduction method of the negative electrode active material involved in the present embodiment, a negative electrode active material with excellent rapid charge and discharge characteristics can be obtained.

[0082] 3. Recovery of negative electrode active material (negative electrode active material obtained in recovery step S40)

[0083] The negative electrode active material obtained by the negative electrode active material reproduction method according to the present embodiment (hereinafter also referred to as "recovered negative electrode active material") is a negative electrode active material prepared as described above, and its surface is amorphized by the charging step S20 and the discharging step S30. That is, it has characteristics different from those of the negative electrode active material contained in the lithium ion secondary battery 1 prepared in the preparation step S10. The characteristics of the recovered negative electrode active material are described below.

[0084] The recovered negative electrode active material is equivalent to the carbon material in the negative electrode active material to be prepared. In other words, the surface of the carbon material of the recovered negative electrode active material is amorphized by the charging step S20 and the discharging step S30. The recovered negative electrode active material is a particulate material that can reversibly occlude and release charge carriers. As for the active material substrate, carbon materials such as graphite, hard carbon, and soft carbon are typically used. The graphite can be natural graphite or artificial graphite.

[0085] As an example of an index related to the surface properties of the recovered negative electrode active material according to the present embodiment, the D band intensity (I D ) and G band intensity (I G ) ratio (I D / I G ). TheI D / I G The ratio is the average information of the crystallinity at a depth of nanometers from the surface of the negative electrode active material. It should be noted that the "D band intensity (I D ) and G band intensity (I G ) ratio (I D / I G )" can be measured using a known Raman spectrometer as described below. Specifically, a laser with a wavelength of 532nm is used to measure the Raman spectrum of the negative electrode active material. Using this Raman spectrum, the 1350cm -1The peak intensity near the D band is taken as the D band intensity (I D ), find 1590cm -1 The peak intensity near the G band is taken as the G band intensity (I G ), calculate I D / I G The value of can be obtained.

[0086] In several preferred embodiments, it is preferred to use the D band intensity (I D ) and G band intensity (I G ) ratio (I D / I G ) is 0.38 or more. G band intensity (I G ) is an index that typically indicates a regular graphite structure, and the D band intensity (I D ) is an index that typically indicates an irregular graphite structure. That is, it can be said that the I of the recovered negative electrode active material D / I G The larger the ratio, the more suitable the surface of the recovered negative electrode active material is for amorphization. D / I G The larger the ratio, the higher the lithium ion acceptance capacity. In other words, the discharge capacity of the recovered negative electrode active material is improved, and the rapid charge and discharge performance is good. D / I G The ratio is preferably 0.38 or more, more preferably 0.40 or more, further preferably 0.42 or more, and further preferably 0.47 or more. D / I G The upper limit of the ratio is not particularly limited, and may be, for example, 1.0 or less.

[0087] In addition, as another example of an index related to the surface properties of the recovered negative electrode active material involved in the present embodiment, the interlayer distance d(002) of the recovered negative electrode active material based on X-ray diffraction (XRD) can be cited. The interlayer distance d(002) of the negative electrode active material is the average information representing the crystallinity at a depth of micrometers from the surface of the negative electrode active material. It should be noted that the "interlayer distance d(002) of the negative electrode active material" in this specification can be measured by a commercially available X-ray diffraction device using a CuKα ray source according to a known method.

[0088] In several preferred embodiments, the interlayer distance d(002) of the recovered negative electrode active material based on X-ray diffraction (XRD) is preferably Above and The following. The recovered negative electrode active material in this embodiment undergoes the above-mentioned charging step S20 and discharging step S30, thereby making the surface of the negative electrode active material amorphous. Therefore, when it is recovered as a recovered negative electrode active material, the interlayer distance d(002) becomes smaller. The smaller the interlayer distance d(002) of the recovered negative electrode active material is, the more suitably the surface of the recovered negative electrode active material is amorphous, and the insertion or removal of lithium ions of the negative electrode active material becomes easier, so the rapid charge and discharge performance is good. The interlayer distance d(002) of the recovered negative electrode active material is preferably The following are more preferably The following is further preferred The interlayer distance d(002) of the recovered negative electrode active material is preferably above.

[0089] The average particle size (median diameter: D50) of the recovered negative electrode active material is not particularly limited, and is, for example, 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less. It should be noted that the average particle size (D50) of the recovered negative electrode active material can be obtained, for example, by laser diffraction scattering.

[0090] An embodiment of the technology disclosed herein has been described above. The technology disclosed herein is not limited to the above-described embodiment, and includes other embodiments in which various configurations are modified.

[0091] <Application of negative electrode active material>

[0092] The negative electrode active material (recovered negative electrode active material) obtained by the reproduction method involved in the present embodiment is not limited thereto, and can be used as a negative electrode active material of a secondary battery, for example. The secondary battery including the negative electrode active material obtained by the reproduction method involved in the present embodiment can be used in various applications, for example, it can be preferably used as a power source (driving power source) for a motor mounted on a vehicle such as a car or a truck. There is no particular limitation on the type of vehicle, for example, plug-in hybrid electric vehicles (PHEV; Plug-in Hybrid Electric Vehicle), hybrid electric vehicles (HEV; Hybrid Electric Vehicle), electric vehicles (BEV; Bat tery Electric Vehicle), etc. can be listed. The secondary battery can also be preferably used as a battery pack in which a plurality of secondary batteries are arranged in a predetermined arrangement direction and a load is applied from the arrangement direction by a restraining mechanism. The shape of the secondary battery is not limited to a square, and can be a coin type, a button type, a cylindrical type, etc. In addition, it can also be constituted as a secondary battery including a stacked shell.

[0093] Hereinafter, examples related to the technology disclosed herein will be described, but the technology disclosed herein is not intended to be limited to the implementation modes shown in these examples.

[0094] <Study Example 1: Study of charging and discharging conditions>

[0095] [Preparation of lithium-ion secondary battery]

[0096] (Example 1)

[0097] First, a used lithium ion secondary battery is prepared in which an electrode body including a positive electrode, a negative electrode, and a separator, and an electrolyte solution are housed in a case.

[0098] As the positive electrode, a positive electrode core made of aluminum is provided with a LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The positive electrode has a positive electrode active material layer with O2 (lithium nickel cobalt manganese composite oxide) as the positive electrode active material.

[0099] As the negative electrode, a negative electrode having a negative electrode core made of copper and a negative electrode active material layer containing natural graphite as a negative electrode active material provided on the surface of the negative electrode core was prepared.

[0100] As the above-mentioned electrolyte, an electrolyte solution prepared by dissolving LiPF6 as a supporting salt in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC=30:30:40 in a concentration of 1 mol / L is prepared.

[0101] [Charging process]

[0102] The lithium ion secondary battery prepared as described above was charged by constant current constant voltage (CCCV) at a charge rate of 0.1 C in a temperature environment of 25° C. until the SOC at the end of charging reached 100%.

[0103] [Discharge process]

[0104] The lithium ion secondary battery subjected to the charging step was subjected to constant current constant voltage (CCCV) discharge at a discharge rate of 1 C in a temperature environment of 25° C. until the SOC at the end of discharge reached 10%.

[0105] [Recovery of negative electrode active materials]

[0106] The lithium-ion secondary battery that has been subjected to the discharge process is disassembled, and the negative electrode is taken out. The negative electrode active material layer is peeled off from the negative electrode by washing with water. The negative electrode active material is recovered from the negative electrode active material layer and dried at 100° C. to remove moisture. In this way, the powdered negative electrode active material is recovered.

[0107] (Example 2~Example 4)

[0108] In Examples 2 to 4, lithium ion secondary batteries having the same configuration as in Example 1 were prepared and charged at the charge rates shown in Table 1. Otherwise, the charging and discharging steps were carried out under the same conditions as in Example 1, and the negative electrode active materials involved in Examples 2 to 4 were recovered.

[0109] (Example 5~Example 6)

[0110] In Examples 5 and 6, lithium ion secondary batteries having the same configuration as in Example 1 were prepared, and the charging process was performed until the SOC at the end of charging reached the values ​​shown in Table 1. Otherwise, the charging process and the discharging process were performed under the same conditions as in Example 1, and the negative electrode active materials involved in Examples 5 and 6 were recovered.

[0111] (Example 7~Example 10)

[0112] In Examples 7 to 10, lithium ion secondary batteries having the same configuration as in Example 1 were prepared and charged at the discharge rates shown in Table 1. Otherwise, the charging and discharging steps were carried out under the same conditions as in Example 1, and the negative electrode active materials of Examples 7 to 10 were recovered.

[0113] (Example 11~Example 14)

[0114] In Examples 11 to 14, lithium ion secondary batteries having the same configuration as in Example 1 were prepared, and the discharge process was performed until the SOC at the end of discharge reached the value described in Table 1. Otherwise, the charging process and the discharging process were performed under the same conditions as in Example 1, and the negative electrode active materials involved in Examples 11 to 14 were recovered.

[0115] (Example 15)

[0116] In Example 15, a lithium ion secondary battery having the same structure as in Example 1 was prepared. In Example 15, the negative electrode active material was directly recovered without performing the charging step and the discharging step. The other procedures were the same as in Example 1.

[0117] [Evaluation of interlayer distance d(002) of recovered negative electrode active material]

[0118] For the recovered negative electrode active materials involved in Examples 1 to 15 (hereinafter also referred to as "recovered negative electrode active materials"), the recovered negative electrode active materials were evaluated. First, the interlayer distance d(002) of the recovered negative electrode active materials using X-ray diffraction (XRD) was evaluated. Specifically, for the recovered negative electrode active material particles, XRD measurement was performed under the following conditions. The results are shown in Table 1.

[0119] Measuring device: Smart Lab (manufactured by Rigaku Co., Ltd.)

[0120] Measurement method: wide angle method

[0121] Radiation source: CuKα radiation

[0122] Measuring range: 5~90°

[0123] Voltage: 45kV

[0124] Current: 200mA

[0125] [Raman peak intensity ratio of recovered negative electrode active material (I D / I G )'s review]

[0126] Next, the Raman peak intensity ratio (I D / I G Specifically, a commercially available microscopic laser Raman analyzer (manufactured by Thermo Fisher Scientific) was used to obtain a Raman spectrum under the following conditions. The 1470 cm -1 The peak intensity is set as I D , 1570cm -1 The peak intensity is set as I G , calculate the Raman peak intensity ratio (I D / I G ). The above Raman spectrum measurement was performed 10 times (n=10), and the average value was calculated. The results are shown in Table 1.

[0127] Objective lens: 50x

[0128] Laser wavelength: 532nm

[0129] Laser output: 1mV

[0130] [Preparation of coin battery cell for evaluation]

[0131] In order to evaluate the performance of the recovered negative electrode active material, a coin cell as a monopolar battery cell in which a negative electrode as a working electrode and metallic lithium as a counter electrode are opposite each other is prepared. First, a negative electrode is prepared using the recovered negative electrode active material. Specifically, the recovered negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are mixed with ion exchange water as a solvent in a solid content mass ratio of recovered negative electrode active material: SBR: CMC = 98:1:1 to prepare a negative electrode paste. The negative electrode paste is applied to one side of a long sheet of copper foil (10 μm thick) as a negative electrode core (negative electrode collector), and after drying, it is pressed using a roller press to prepare a sheet-like negative electrode. The sheet-like negative electrode is punched out to the size of a coin cell, and the weight (g) of the punched negative electrode is measured. The weight of the negative electrode core was subtracted from the weight of the negative electrode, and the resultant value was multiplied by 0.98 (ratio of the recovered negative electrode active material to the entire negative electrode active material layer) and was defined as the weight (g) of the negative electrode active material.

[0132] As the separator, a 24 μm thick porous polyolefin sheet having a three-layer structure of PP / PE / PP was used. In addition, a separator having a ceramic layer (4 μm thick) of alumina (Al2O3), boehmite, etc. coated on one side was used.

[0133] As an electrolyte solution, an electrolyte solution prepared by dissolving LiPF6 as a supporting salt in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:30:40 to a concentration of 1.0 mol / L was prepared.

[0134] The negative electrode, separator, and metal lithium are stacked in this order and impregnated with an electrolyte to produce a coin cell. At this time, the ceramic layer of the separator is stacked so that it faces the negative electrode.

[0135] [Evaluation of discharge specific capacity]

[0136] Using the evaluation coin battery cells obtained above, the discharge specific capacity of the recovered negative electrode active materials involved in Examples 1 to 15 was evaluated. Specifically, each evaluation coin battery cell was placed in an environment of 25°C, and the lithium electrode was charged with a constant current at a current rate of 0.2C until 3mV, and then, constant voltage charging was performed with a constant voltage of 3mV until the current rate became 1 / 10C. Then, for each evaluation coin battery cell, the lithium electrode was discharged with a constant current value of 0.2C until 1.6V, and then, constant voltage discharge was performed with a constant voltage of 1.6V until the current rate became 1 / 10C. In this way, the discharge capacity (mAh) at 0.2C discharge was calculated. The discharge specific capacity (mAh / g) of the negative electrode active material is calculated from the discharge capacity and the weight (g) of the negative electrode active material. The results are shown in Table 1.

[0137] [Evaluation of rate performance]

[0138] Next, the above-mentioned evaluation coin battery cells are used as indicators of the rapid charge and discharge performance of the recovered negative electrode active materials involved in Examples 1 to 15 to evaluate the rate performance. Specifically, each evaluation coin battery cell after the above-mentioned discharge specific capacity measurement is placed in an environment of 25°C, and the lithium electrode is charged with a constant current at a current rate of 1C until 3mV, and then, a constant voltage charge is performed with a constant voltage of 3mV until the current rate becomes 1 / 10C. Then, for each evaluation coin battery cell, a constant current discharge is performed with a current value of 1C to the lithium electrode until 1.6V, and then a constant voltage discharge is performed with a constant voltage of 1.6V until the current rate becomes 1 / 10C. In this way, the discharge capacity (mAh) at 1C discharge is calculated. Using the discharge capacity (mAh) at 1C discharge and the discharge capacity (mAh) at 0.2C discharge measured during the above-mentioned evaluation of the discharge specific capacity, the rate performance (%) is calculated according to the following formula (1). The higher the value of the rate performance (%) is, the better the charge-discharge performance of the recovered negative electrode active material is.

[0139] Rate performance (%) = (discharge capacity at 1C discharge (mAh) / discharge capacity at 0.2C discharge (mAh)) × 100 ···Formula (1)

[0140] [Table 1]

[0141]

[0142] As shown in the results of Table 1, in Example 1, compared with Example 15 in which the negative electrode active material was recovered without performing the charging and discharging steps, the D / I Gand interlayer distance d(002), good results were obtained. In addition, good results were obtained for the discharge specific capacity and rate performance. In addition, from the results of Examples 2 to 4 and Examples 7 to 10, it can be seen that if the discharge rate is relatively higher than the charge rate, when the charge rate and discharge rate are different from those in Example 1, the same as in Example 1 for I D / I G and interlayer distance d(002), good results were obtained. In addition, good results were obtained for discharge specific capacity and rate performance. In addition, for Example 1 and Examples 5 and 6 with different charge termination SOCs, and Examples 11 to 14 with different discharge termination SOCs, the results of I D / I G Good results were also obtained for the interlayer distance d(002), and good results were also obtained for the discharge specific capacity and rate performance.

[0143] <Study Example 2: Study on the Positive and Negative Electrode Capacity Ratio in the Lithium-ion Secondary Battery to be Prepared>

[0144] (Example 16~Example 21)

[0145] Among them, the positive and negative electrode capacity ratios in the lithium-ion secondary batteries to be prepared are studied. Specifically, in Examples 16 to 21, lithium-ion secondary batteries having the same structure as in Example 1 are prepared except that the positive and negative electrode capacity ratios are as shown in Table 2. Then, for the lithium-ion secondary batteries involved in Examples 16 to 21, the charging process and the discharging process are carried out under the same conditions as in Example 1, and the negative electrode active materials involved in Examples 16 to 21 are recovered (hereinafter referred to as "recovered negative electrode active materials"). For the recovered negative electrode active materials involved in Examples 16 to 21, the same evaluation as in Study Example 1 is performed. The results are shown in Table 2. Then, evaluation coin battery cells involved in Examples 16 to 21 are prepared, and the same evaluation as in Study Example 1 is performed. The results are shown in Table 2.

[0146] [Table 2]

[0147] Table 2

[0148]

[0149] As shown in the results of Table 2, for all examples 16 to 21 in which the positive-negative electrode capacity ratio was greater than 1.0, compared with Example 15 in which the negative electrode active material was recovered without performing the charging and discharging steps, good results were obtained in both discharge specific capacity and rate performance.

[0150] As described above, specific aspects of the technology disclosed herein include aspects described in the following items.

[0151] Item 1: A method for reproducing negative electrode active materials, which is a method for reproducing negative electrode active materials from used lithium-ion secondary batteries, comprising: a preparation step, wherein a used lithium-ion secondary battery including a positive electrode, a negative electrode having a negative electrode active material containing a carbon material, and an electrolyte is prepared; a charging step, wherein the lithium-ion secondary battery is charged; a discharging step, which is a step of discharging the lithium-ion secondary battery after the charging step, wherein the discharge is performed at a discharge rate higher than the charging rate of the charging step; and a recovery step, wherein, for the lithium-ion secondary battery after the discharging step, the negative electrode active material containing the carbon material is recovered from the negative electrode.

[0152] Item 2: The method for reproducing a negative electrode active material according to Item 1, wherein the positive-negative electrode capacity ratio (negative electrode capacity / positive electrode capacity) of the lithium ion secondary battery prepared in the preparation step is 1.0 or more.

[0153] Item 3: The method for reproducing a negative electrode active material according to Item 1 or 2, wherein the charging step is performed at a charging rate of 0.5 C or less.

[0154] Item 4: The method for reproducing a negative electrode active material according to any one of Items 1 to 3, wherein the charging step is performed until the state of charge (SOC) of the lithium ion secondary battery reaches 50% or more.

[0155] Item 5: The method for reproducing a negative electrode active material according to any one of Items 1 to 4, wherein the discharge step is performed at a discharge rate of 0.5 C or more.

[0156] Item 6: The method for reproducing a negative electrode active material according to any one of Items 1 to 5, wherein the discharge step is performed until the SOC of the lithium ion secondary battery becomes 30% or less.

[0157] Item 7: The method for reproducing a negative electrode active material according to any one of Items 1 to 6, wherein the D band intensity (I D ) and G band intensity (I G ) ratio (I D / I G ) is greater than 0.38.

[0158] Item 8: The method for reproducing the negative electrode active material according to Item 7, wherein the interlayer distance d(002) of the negative electrode active material recovered in the recovery step based on X-ray diffraction is Above and the following.

Claims

1. A method for reproducing negative electrode active materials is a method for reproducing negative electrode active materials from used lithium-ion secondary batteries, comprising: Preparation process, including preparing a used lithium ion secondary battery including a positive electrode, a negative electrode having a negative electrode active material including a carbon material, and an electrolyte; A charging process, wherein the lithium-ion secondary battery is charged; a discharging step of discharging the lithium ion secondary battery after the charging step, wherein the discharging is performed at a discharge rate higher than the charge rate in the charging step; and A recovery step of recovering the negative electrode active material including a carbon material from the negative electrode of the lithium ion secondary battery after the discharge step.

2. The method for reproducing the negative electrode active material according to claim 1, wherein: The lithium ion secondary battery prepared in the preparation step has a positive electrode to negative electrode capacity ratio (negative electrode capacity / positive electrode capacity) of 1.0 or more.

3. The method for reproducing the negative electrode active material according to claim 1 or 2, wherein: The charging step is performed at a charging rate of 0.5C or less.

4. The method for reproducing a negative electrode active material according to claim 1 or 2, wherein: The charging step is performed until the state of charge (SOC) of the lithium ion secondary battery reaches 50% or more.

5. The method for reproducing the negative electrode active material according to claim 1 or 2, wherein: The discharge step is performed at a discharge rate of 0.5 C or more.

6. The method for reproducing the negative electrode active material according to claim 1 or 2, wherein: The discharge step is performed until the SOC of the lithium ion secondary battery becomes 30% or less.

7. The method for reproducing a negative electrode active material according to claim 1 or 2, wherein: The D band intensity (I D ) and G band intensity (I G ) ratio (I D / I G ) is greater than 0.

38.

8. The method for reproducing the negative electrode active material according to claim 7, wherein: The interlayer distance d(002) of the negative electrode active material recovered in the recovery step based on the X-ray diffraction method is Above and the following.

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