Subcritical mixture and its application in recycling metal elements in lithium batteries

Abstract

The present invention provides a subcritical mixture and its application in recovering metal elements in lithium batteries, belonging to the technical field of biomass resource utilization and waste lithium battery recycling. The present invention provides a subcritical mixture, whose components include water and biomass, the temperature is 150-300℃±3℃, and the pressure is 0.4-8.7MPa. The present invention also provides the application of this subcritical mixture in recovering metal elements in lithium batteries. The subcritical mixture described in the present invention is used to process waste lithium-ion batteries to obtain lithium carbonate and metal oxides, and the lithium element leaching rate is high; biomass, especially waste biomass such as sawdust, straw, and husks, is used as raw materials to achieve green processing and resource recycling, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass resource utilization and waste lithium battery recycling, and relates to a subcritical mixture and application thereof in recycling metal elements in lithium batteries. Background Art

[0002] Due to the rapid development of new energy vehicles and renewable energy, the demand for lithium-ion batteries (LIBs) has increased rapidly. Lithium-ion batteries have the advantages of high energy density, long cycle life, and fast charge and discharge speed. They are one of the most popular energy storage materials and are widely used in renewable grid energy storage systems, electric vehicles, portable electronic devices and other fields. Due to the limited service life of lithium-ion batteries (generally 3 years for portable electronic devices and 5-10 years for electric vehicles), a large amount of waste lithium-ion batteries are being generated. It is estimated that by 2030, the global production of waste lithium-ion batteries will reach 11 million tons. However, the current recycling rate of waste lithium-ion batteries is less than 6%, and most of them are landfilled or incinerated, causing serious ecological environmental pollution and waste of resources. Therefore, it is urgent to recycle waste lithium-ion batteries to avoid environmental pollution and waste of resources and implement the concept of circular economy.

[0003] In industry, the process of recovering valuable metals from waste lithium-ion batteries is mainly based on pyrometallurgy and hydrometallurgy. Traditional pyrometallurgy requires melting the entire waste lithium-ion battery at an extremely high reaction temperature (≥1400°C) to generate an alloy. Although this technology has reduced process steps and compatibility, it has high energy consumption and releases a large amount of toxic fumes. Compared with pyrometallurgy, hydrometallurgy is favored by many researchers due to its advantages such as high metal recovery rate, selective recovery, and high product purity. However, its complex process steps, high acid consumption, the need to use expensive reagents, and the generation of a large amount of toxic wastewater still hinder its application in industry. In the hydrometallurgical process, hydrogen peroxide (H2O2) is usually added as a reducing agent to improve the efficiency of acid leaching, but hydrogen peroxide has the disadvantages of being dangerous, explosive, and costly. Therefore, it is urgent to develop green, efficient, short-process, and low-cost alternatives to recover valuable metals from waste lithium-ion batteries. Existing technology

[0004] Chinese patent application 202211699472.1 discloses a method for recovering the positive electrode material of waste lithium cobalt oxide batteries by reducing biomass pyrolysis gas. The method immerses the recovered waste lithium battery in a salt solution for discharge, and obtains a positive electrode material sheet by disassembling and separating; vacuum pyrolysis of the positive electrode material sheet and scraping out to obtain lithium cobalt oxide powder; suspend the lithium cobalt oxide powder above the lignocellulosic biomass and ensure that the two are separated, and heat at 400-500°C in an oxygen-free atmosphere, and reduce the lithium cobalt oxide by biomass pyrolysis gas to obtain a reaction product; the reaction product is leached by water immersion and filtered to obtain a filtrate and a filter residue; the filtrate is evaporated to obtain lithium carbonate powder, and the filter residue is dried to obtain Co oxide. However, this method requires the generation of pyrolysis gas in an oxygen-free atmosphere at a temperature of 400-500°C, and the reaction conditions are difficult to control.

[0005] Chinese patent application 202010166395.8 discloses a method for recycling and regenerating waste lithium battery cathode materials with the assistance of biomass fertilizers, including six steps: reduction roasting, water leaching, preparation of lithium source, acid leaching, preparation of ternary precursor, and preparation of ternary cathode materials. Among them, reduction roasting needs to be carried out at 700-800°C under a protective atmosphere (argon), the reaction conditions are relatively harsh, and the use of argon greatly increases the process cost.

[0006] Chinese patent application 201911049842.5 discloses a method for recycling retired lithium-ion battery positive electrode materials using a hydrothermal method. Organic acid and sugar reducing agent are added to the mixed solution, the reactor is sealed, and heated at 100-300°C to obtain a black turbid liquid. The black turbid liquid is filtered to obtain a leachate containing valuable metal ions. However, the metal ion solution obtained by this method is a mixed metal ion solution. If a pure lithium salt is to be obtained, the substances in the ion solution must be separated, which is complicated and increases the processing cost.

[0007] Chinese patent application 202010167038.3 discloses a method for fully recovering valuable metal elements in the positive electrode plates of waste power lithium batteries. The specific steps are: pre-hydrothermally react the biomass under weak acid conditions to separate the biomass solution 1 and the filter residue, and then react the filter residue under alkaline solution to obtain biomass solution 2. Peel off the waste positive electrode plates in the biomass solution 2, separate the aluminum metal and the positive electrode slurry, and then reduce and leach the positive electrode slurry and biomass solution 1 under acid to obtain a leachate enriched with lithium, nickel, cobalt, and manganese. However, in this method, various metals are mixed in the same leachate, and it takes extra time and reagents to extract lithium salts from the leachate; and the reaction process involves acid and alkaline solutions, and the steps are relatively complicated.

[0008] In summary, it is difficult for the existing technology to provide a green, efficient, convenient and low-cost method to simultaneously recycle lithium elements and metal oxides in waste lithium-ion batteries. Summary of the invention

[0009] In view of this, in view of the problem that the prior art is difficult to provide a green, efficient, convenient and low-cost method to simultaneously recover lithium elements and metal oxides in waste lithium-ion batteries, the purpose of the present invention is to provide a subcritical mixture and its application in recovering metal elements in lithium batteries.

[0010] To achieve the above-mentioned purpose of the invention, on the one hand, the present invention provides a subcritical mixture, wherein the components of the subcritical mixture include water and biomass, the temperature is 150-300°C±3°C, and the pressure is 0.4-8.7MPa.

[0011] The water includes but is not limited to pure water, tap water, deionized water, purified water, etc.

[0012] The biomass includes but is not limited to lignocellulosic biomass.

[0013] Preferably, the temperature of the subcritical mixture is 150-300°C±3°C, and the pressure is 0.4-8.7 MPa.

[0014] More preferably, the temperature of the subcritical mixture is 160-280°C±3°C, and the pressure is 0.5-6.5 MPa.

[0015] More preferably, the temperature of the subcritical mixture is 200-280°C±3°C, and the pressure is 1.5-6.5MPa.

[0016] Preferably, the biomass comprises lignocellulosic biomass.

[0017] Preferably, the lignocellulosic biomass includes wood chips, straw, husks, leaves, cellulose and lignin.

[0018] More preferably, the lignocellulosic biomass includes at least one of wood chips, straw, peanut shells, rice husks, cellulose, lignin, and dried leaves.

[0019] More preferably, the lignocellulosic biomass is selected from at least one of sawdust, straw, peanut shells, rice husks, cellulose, lignin, and dried leaves.

[0020] Further preferably, and as an example of the present invention, the wood-based cellulosic biomass is selected from any one of bamboo sawdust, pine sawdust, corn straw, wheat straw, peanut shell, rice husk, cellulose, lignin, and dried bamboo leaves.

[0021] As a preferred embodiment of the present invention, the lignocellulosic biomass is bamboo sawdust.

[0022] Preferably, the mass volume ratio of the biomass to water is 0.1-10 g:50 mL.

[0023] More preferably, the mass volume ratio of the biomass to water is 0.6-5 g:50 mL.

[0024] More preferably, the mass volume ratio of the biomass to water is 0.6-2 g:50 mL.

[0025] Further preferably, the mass volume ratio of biomass to water is 0.8-1 g:50 mL.

[0026] On the other hand, the present invention provides a method for preparing a subcritical mixture, comprising the following steps: adding a formula of water and biomass into a sealed reactor, heating, and obtaining a subcritical mixture.

[0027] Preferably, the volume ratio of the water to the solvent in the sealed reactor is 50-120 mL:200 mL.

[0028] More preferably, the volume ratio of the water to the solvent in the sealed reactor is 50-100 mL:200 mL.

[0029] In another aspect, the present invention provides an application of a subcritical mixture in recovering metal elements in a lithium battery, characterized in that the method comprises the following steps:

[0030] S1. Mixing lithium-containing materials, water and biomass in lithium batteries, increasing temperature and pressure, reacting, filtering, and obtaining filtrate and filter residue;

[0031] S2, adding sodium carbonate to the filtrate in step S1, filtering, and obtaining lithium carbonate;

[0032] The temperature and pressure increase in step S1 specifically refers to the temperature being increased to 150-300°C±3°C and the pressure being increased to 0.4-8.7MPa.

[0033] In step S1, the water includes but is not limited to pure water, tap water, deionized water, purified water, etc.

[0034] In step S1, the lithium battery includes but is not limited to ternary NCM (LiNi x Co y Mn z O2) lithium battery, lithium cobalt oxide (LiCoO2) lithium battery, lithium manganese oxide (LiMn2O4) lithium battery, Co Al co-doped lithium nickel oxide NCA (LiNi x Co y Al zO2) lithium battery, etc.

[0035] Preferably, the biomass in step S1 includes lignocellulosic biomass.

[0036] Preferably, the lignocellulosic biomass includes wood chips, straw, husks, leaves, cellulose and lignin.

[0037] More preferably, the lignocellulosic biomass includes at least one of wood chips, straw, peanut shells, rice husks, cellulose, lignin, and dried leaves.

[0038] More preferably, the lignocellulosic biomass is selected from at least one of sawdust, straw, peanut shells, rice husks, cellulose, lignin, and dried leaves.

[0039] Further preferably, and as an example of the present invention, the wood-based cellulosic biomass is selected from any one of bamboo sawdust, pine sawdust, corn straw, wheat straw, peanut shell, rice husk, cellulose, lignin, and dried bamboo leaves.

[0040] As a preferred embodiment of the present invention, the lignocellulosic biomass is bamboo sawdust.

[0041] Preferably, in step S1, the mass volume ratio of the biomass to the water is 0.1-10 g:50 mL.

[0042] More preferably, the mass volume ratio of the biomass to water is 0.6-5 g:50 mL.

[0043] More preferably, the mass volume ratio of the biomass to water is 0.6-2 g:50 mL.

[0044] Further preferably, the mass volume ratio of biomass to water is 0.8-1 g:50 mL.

[0045] Preferably, the lithium battery in step S1 is selected from ternary NCM (LiNi x Co y Mn z O2) lithium battery, lithium cobalt oxide (LiCoO2) lithium battery, lithium manganese oxide (LiMn2O4) lithium battery, Co Al co-doped lithium nickel oxide NCA (LiNi x Co y Al z O2) At least one of the lithium-containing materials in the lithium battery.

[0046] More preferably, the lithium battery in step S1 is selected from at least one of a ternary NCM lithium battery, a lithium cobalt oxide lithium battery, and a lithium manganese oxide lithium battery.

[0047] More preferably, the lithium battery in step S1 is selected from one of a ternary NCM lithium battery, a lithium cobalt oxide lithium battery, and a lithium manganese oxide lithium battery.

[0048] The lithium-containing materials include but are not limited to lithium-containing electrode materials, lithium-containing dielectric materials, and the like.

[0049] Preferably, the lithium-containing material is selected from at least one of electrode materials and black powder.

[0050] More preferably, the electrode material is selected from at least one of a positive electrode material and a negative electrode material.

[0051] More preferably, the preparation method of the black powder is as follows:

[0052] The waste lithium batteries are pre-treated by drying, mechanical crushing and sorting to obtain black powder containing positive electrode materials and negative electrode materials.

[0053] Preferably, in step S1, the mass ratio of the lithium-containing material to the biomass is 0.1-1.2:1.

[0054] More preferably, in step S1, the mass ratio of the lithium-containing material to the biomass is 0.6-1.2:1.

[0055] More preferably, in step S1, the mass ratio of the lithium-containing material to the biomass is 0.8-1:1.

[0056] Preferably, the reaction in step S1 is specifically carried out as follows: maintaining a temperature of 150-300°C±3°C and a pressure of 0.4-8.7MPa.

[0057] More preferably, the reaction in step S1 is specifically carried out as follows: maintaining a temperature of 160-280°C ± 3°C and a pressure of 0.5-6.5 MPa.

[0058] More preferably, the reaction in step S1 is specifically carried out as follows: maintaining the temperature at 200-280°C±3°C and the pressure at 1.5-6.5MPa.

[0059] Preferably, the reaction time of the reaction is 1-30h.

[0060] More preferably, the reaction time of the reaction is 4-24h.

[0061] More preferably, the reaction time of the reaction is 20-24h.

[0062] Preferably, in step S2, before adding sodium carbonate to the filtrate, the temperature of the filtrate is adjusted to 10-50°C, the pH is adjusted to 6-8, and the filtrate is dried after filtering.

[0063] Preferably, the application further comprises step S3, which is as follows:

[0064] S3, washing the filter residue described in step S1 to obtain metal oxide.

[0065] Preferably, the metal oxide in step S3 is specifically: black powder containing metal oxide.

[0066] Preferably, in step S3, the washing is washing with water, and drying is performed after the washing.

[0067] More preferably, the washing with water is washing with deionized water.

[0068] More preferably, the washing with deionized water is washing with deionized water 2-3 times.

[0069] More preferably, the drying is oven drying.

[0070] More preferably, the drying is carried out at 40-80°C.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) The present invention provides a novel subcritical mixture and its application in recovering metal elements in lithium batteries, achieving a high lithium leaching rate and obtaining metal oxides after de-lithiation.

[0073] (2) The subcritical mixture provided by the present invention is used to recycle lithium battery related materials, overcoming the harsh reaction conditions of about 800°C and the complex processing flow in the traditional "roasting reduction-water leaching of lithium" process, and achieving efficient recovery of lithium carbonate.

[0074] (3) The subcritical mixture provided by the present invention utilizes biomass, especially biomass waste such as sawdust, straw, and husk, thereby achieving effective integrated utilization of ecological resources while reducing costs. In addition, the process steps of the method are simple, and the mixture formula is green and pollution-free, which has great industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is a technical flow chart of the application of a subcritical mixture in recovering metal elements in lithium batteries provided in Example 1 of the present invention.

[0076] Figure 2 It is the X-ray diffraction (XRD) diagram of the filter residue after the reaction of the present invention, wherein the 6 X-ray diffraction diagrams from top to bottom correspond to Example 1, Example 2, Example 13, Example 14, Comparative Example 6, and Comparative Example 5, respectively.

[0077] Figure 3This is the X-ray diffraction (XRD) diagram of the filter residue after NCM811 reaction without adding biomass in the present invention, wherein the 6 X-ray diffraction diagrams from top to bottom correspond to Comparative Example 1.1, Comparative Example 1.2, Comparative Example 1.3, Comparative Example 1.4, Comparative Example 1.5, and Comparative Example 1.6, respectively.

[0078] Figure 4 This is the X-ray diffraction (XRD) diagram of the filter residue after the NCM black powder reaction without adding biomass in the present invention, wherein the 6 X-ray diffraction diagrams from top to bottom correspond to Comparative Example 2.1, Comparative Example 2.2, Comparative Example 2.3, Comparative Example 2.4, Comparative Example 2.5, and Comparative Example 2.6, respectively. DETAILED DESCRIPTION

[0079] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of the present invention.

[0080] The present invention is further described below by way of specific examples. The various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified. Unless otherwise specified, the contents described below are all weight contents. Unless otherwise specified, it is understood that the process is carried out at room temperature.

[0081] Example 1

[0082] A subcritical mixture is used to recover metal elements in lithium batteries, and the steps are as follows:

[0083] S1. Dry, mechanically crush and sort the recycled waste lithium batteries to obtain black powder (NCM black powder) containing positive electrode materials and negative electrode materials of nickel, cobalt and manganese. Add 1g NCM black powder, 1g bamboo sawdust and 50mL deionized water to a reactor with a volume of 200mL and stir well. The closed reactor is placed in an oven and heated to a temperature of 280±3℃ and a pressure of 6.5MPa for 24h to react. After the reaction is completed, cool naturally to room temperature, filter, and obtain filter residue and filtrate. The efficiency of lithium ion leaching is measured by inductively coupled plasma atomic emission spectrometer (ICP-OES) to be 94.48%.

[0084] S2. The filtrate obtained in step S1 is adjusted to a temperature of 10-50° C. and a pH of 6-8, and an excess of saturated sodium carbonate solution is added, and the mixture is stirred and mixed to form a white precipitate. The white precipitate is filtered and dried to obtain white lithium carbonate powder.

[0085] S3. Wash the filter residue obtained in step S1 with deionized water for 2-3 times and dry at 40-80° C. to obtain a black powder containing metal oxides.

[0086] The flow chart of the above reaction process is as follows Figure 1 shown.

[0087] The metal oxide obtained in step S3 was characterized by X-ray diffraction, and the results are as follows: Figure 2 As shown. Among them, the transition metal phase is composed of LiNi x Co y Mn z O2 is reduced to NiO, CoO, and MnO2.

[0088] Example 2

[0089] Compared with Example 1, in step S1, the heating in the oven is changed to a temperature of 240±3° C. and a pressure of 3.3 MPa, and the rest are the same.

[0090] Example 3

[0091] Compared with Example 1, in step S1, the holding time is changed to 20 hours, and the rest are the same.

[0092] Example 4

[0093] Compared with Example 1, in step S1, the amount of bamboo sawdust is changed to 0.8 g, and the rest is the same.

[0094] Example 5

[0095] Compared with Example 2, in step S1, the black powder is replaced with waste lithium manganese oxide positive electrode material of equal mass, and the rest is the same.

[0096] Example 6

[0097] Compared with Example 2, in step S1, the black powder is replaced with waste lithium cobalt oxide positive electrode material of equal mass, and the rest is the same.

[0098] Example 7

[0099] Compared with Example 1, in step S1, the bamboo sawdust is replaced with pine sawdust powder of equal mass, and the rest are the same.

[0100] Example 8

[0101] Compared with Example 1, in step S1, the bamboo sawdust is replaced with corn stalks of equal mass, and the rest are the same.

[0102] Example 9

[0103] Compared with Example 1, in step S1, the bamboo sawdust is replaced with wheat straw of equal mass, and the rest is the same.

[0104] Example 10

[0105] Compared with Example 1, in step S1, the bamboo sawdust is replaced with rice straw of equal mass, and the rest are the same.

[0106] Embodiment 11

[0107] Compared with Example 1, in step S1, the bamboo sawdust is replaced with peanut shells of equal mass, and the rest are the same.

[0108] Example 12

[0109] Compared with Example 1, in step S1, the bamboo sawdust is replaced with rice husks of equal mass, and the rest are the same.

[0110] Embodiment 13

[0111] Compared with Example 1, in step S1, the heating in the oven is changed to a temperature of 200±3° C. and a pressure of 1.5 MPa, and the rest are the same.

[0112] Embodiment 14

[0113] Compared with Example 1, in step S1, the heating in the oven is changed to a temperature of 160±3° C. and a pressure of 0.5 MPa, and the rest are the same.

[0114] Embodiment 15

[0115] Compared with Example 1, in step S1, the amount of bamboo sawdust is changed to 1.2 g, and the rest is the same.

[0116] Example 16

[0117] Compared with Example 1, in step S1, the amount of bamboo sawdust is changed to 0.6 g, and the rest are the same.

[0118] Embodiment 17

[0119] Compared with Example 2, in step S1, the bamboo sawdust is replaced with cellulose of equal mass, and the rest are the same.

[0120] Embodiment 18

[0121] Compared with Example 2, in step S1, the bamboo sawdust is replaced with lignin of equal mass, and the rest are the same.

[0122] Comparative Example 1.1

[0123] Compared with Example 1, in step S1, NCM black powder is replaced by NCM811 positive electrode material, and bamboo sawdust is not added. At this time, the system pressure is 8.7 MPa, and the rest are the same.

[0124] Comparative Example 1.2

[0125] Compared with Comparative Example 1.1, in step S1, the heating in the oven is changed to a temperature of 240±0.1° C. and a pressure of 3.3 MPa, and the rest are the same.

[0126] Comparative Example 1.3

[0127] Compared with comparative example 1.1, in step S1, the heating in the oven is changed to a temperature of 200±0.1°C and a pressure of 1.5 MPa, and the rest are the same.

[0128] Comparative Example 1.4

[0129] Compared with comparative example 1.1, in step S1, the heating in the oven is changed to a temperature of 260±0.1° C. and a pressure of 0.5 MPa, and the rest are the same.

[0130] Comparative Example 1.5

[0131] Compared with Comparative Example 1.1, in step S1, the heating in the oven is changed to a temperature of 120±0.1° C. and a pressure of 0.1 MPa, and the rest are the same.

[0132] Comparative Example 1.6

[0133] Compared with Comparative Example 1.1, in step S1, the heating in the oven is changed to a temperature of 80±0.1° C. and a pressure of 0.1 MPa, and the rest are the same.

[0134] Comparative Example 2.1

[0135] Compared with comparative example 1.1, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0136] Comparative Example 2.2

[0137] Compared with comparative example 1.2, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0138] Comparative Example 2.3

[0139] Compared with comparative example 1.3, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0140] Comparative Example 2.4

[0141] Compared with comparative example 1.4, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0142] Comparative Example 2.5

[0143] Compared with comparative example 1.5, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0144] Comparative Example 2.6

[0145] Compared with comparative example 1.6, in step S1, the NCM811 positive electrode material is replaced by NCM black powder, and the rest are the same.

[0146] Comparative Example 3

[0147] Compared with Example 1, in step S1, NCM black powder is replaced by lithium manganese oxide positive electrode material, and bamboo sawdust is not added, the temperature is set to 240±3° C., the pressure is set to 3.3 MPa, and the rest are the same.

[0148] Comparative Example 4

[0149] Compared with Comparative Example 3, in step S1, the lithium manganese oxide positive electrode material is replaced by lithium cobalt oxide positive electrode material, and the rest are the same.

[0150] Comparative Example 5

[0151] Compared with Example 1, in step S1, the closed reactor is operated with an open reflux device, and the other steps are the same. At this time, the reaction system is not a subcritical mixture system, and the temperature of the reaction system measured by the thermometer is 80° C. and the pressure is one atmosphere.

[0152] Comparative Example 6

[0153] Compared with Example 1, in step S1, the temperature is 120±3° C., the pressure is ˜0.1 MPa, and the rest are the same.

[0154] Comparative Example 7

[0155] Compared with Example 1, in step S1, the reaction time is changed to 4 hours, and the rest are the same.

[0156] Comparative Example 8

[0157] Compared with Example 1, in step S1, the amount of bamboo sawdust is changed to 0.2 g, and the rest is the same.

[0158] Experimental results:

[0159] The key experimental conditions and experimental results of each embodiment and comparative example are shown in the following table:

[0160]

[0161]

[0162] From the above experimental results, it can be seen that in Examples 1-20, the lithium-containing materials in waste lithium batteries were recovered by using subcritical mixtures, and the lithium leaching rate reached more than 82.28%, and the highest could reach 99.71%. It is particularly worth noting that, under the same conditions, the lithium leaching rate of the embodiment using bamboo sawdust as biomass is higher than the lithium leaching rate of the embodiment using pine sawdust, rice husk, peanut shell, corn stalk, wheat stalk, rice stalk, lignin, and cellulose.

[0163] In Comparative Examples 1.1-1.6 and Comparative Examples 2.1-2.6, biomass was not used as a component of the subcritical mixture, and the lithium leaching rate was only 6.31%-55.75%. Figure 3 (Comparative Examples 1.1-1.6), Figure 4 (Comparative Examples 2.1-2.6) and Figure 2 By comparison, when biomass is used as a component of the subcritical mixture, as the reaction temperature increases, the positive electrode material NCM first decomposes and then is reduced to NiO, CoO and MnO. When biomass is not used as a component of the subcritical mixture, neither NCM811 nor NCM black powder undergoes phase transformation and forms metal oxides.

[0164] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. Application of a subcritical mixture in recovering metal elements in lithium batteries, characterized in that: The following steps are involved: S1. Mixing lithium-containing materials, water and biomass in lithium batteries, increasing temperature and pressure, reacting, filtering, and obtaining filtrate and filter residue; S2, adding sodium carbonate to the filtrate described in step S1, filtering, and obtaining lithium carbonate; Wherein, in step S1, the biomass is bamboo sawdust, the mass volume ratio of the biomass to the water is 1 g:50 mL, the temperature and pressure increase are specifically the temperature is increased to 280°C±3°C, the pressure is increased to 6.5 MPa, the reaction is specifically maintained at a temperature of 280°C±3°C, a pressure of 6.5 MPa, and a time of 24 hours, the lithium-containing material is NCM black powder, and the mass ratio of the lithium-containing material to the biomass is 1:1; or In step S1, the biomass is bamboo sawdust, the mass volume ratio of the biomass to the water is 0.8 g:50 mL, the temperature and pressure increase are specifically the temperature is increased to 280°C±3°C, the pressure is increased to 6.5 MPa, the reaction is specifically maintained at 280°C±3°C, the pressure is 6.5 MPa, and the time is 24 hours, the lithium-containing material is NCM black powder, and the mass ratio of the lithium-containing material to the biomass is 1:0.8; or, In step S1, the biomass is bamboo sawdust, the mass volume ratio of the biomass to the water is 1g:50mL, the temperature and pressure increase are specifically the temperature is increased to 240℃±3℃, the pressure is increased to 3.3MPa, the reaction is specifically maintained at a temperature of 240℃±3℃, a pressure of 3.3MPa, and a time of 24h, the lithium-containing material is a lithium manganate positive electrode material, and the mass ratio of the lithium-containing material to the biomass is 1:

1.

2. The use according to claim 1, characterized in that: In step S2, before adding sodium carbonate, the temperature of the filtrate is adjusted to 10-50° C. and the pH is 6-8; and after the filtration, a drying step is also included.

3. The use according to claim 1, characterized in that: The step S3 is further included, which is as follows: S3, washing the filter residue described in step S1 to obtain metal oxide.

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