Recycling Method of Waste Graphite, Purified Graphite and Its Application

Abstract

The present invention discloses a method for recycling waste graphite, purified graphite and its applications. The recycling method comprises the following steps: 1) After mixing a composition of an acid and hydrogen peroxide with waste graphite, heating is carried out for aging to obtain aged graphite; 2) After mixing the aged graphite with an acid solution and carrying out microwave treatment, the mixture after microwave treatment is mixed with a promoter and subjected to high-pressure acid leaching treatment to obtain purified graphite; wherein, the promoter is a mixed organic solution, and the mixed organic solution includes phosphate ester. The method of the present invention utilizes aging and acid leaching, in combination with the use of microwave and promoter, to effectively reduce the impurity content and layer spacing, improve the conductivity of graphite. Further, by carrying out high-temperature regeneration on the prepared purified graphite, the impurity content can be further reduced, the conductivity can be improved and the graphitization degree can be increased, thereby improving its electrochemical performance when applied to batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of waste battery recycling, and relates to a recycling method of waste graphite, purified graphite and its application. Background Art

[0002] With the development of the economy, countries around the world have realized the shortage of resources. The output of lithium-ion batteries has also increased rapidly, with an average annual growth rate of more than 32%. Generally, the service life of lithium-ion batteries is about 5 years, and the treatment of these waste batteries has now attracted the attention of countries around the world. As the most commonly used anode material in commercial lithium-ion batteries, graphite accounts for more than 80% of the anode material. Graphite has good electrical conductivity, an ordered crystal structure, and the performance of reversibly storing lithium ions. After a long cycle, the anode graphite in the failed lithium-ion battery still has a complete lattice structure. However, due to the long reaction process, some lithium ions in the layered structure of graphite cannot escape after being embedded, resulting in residues in the active sites of graphite, which is commonly known as "dead lithium". In addition, during the initial cycle of graphite, a solid electrolyte interface passivation film is generated by the side reaction between the electrolyte and graphite, resulting in the failure of the graphite cycle performance.

[0003] At present, a complete and detailed recycling process and industrialized complete process have not been established for the recycling of anode materials like those for cathode materials. And the anode materials in the lithium-ion batteries retired every year will increase year by year, bringing huge pressure to the environment and resource utilization. Therefore, it is urgent to establish the process standards and industrialized processes for anode recycling.

[0004] Currently, the general methods for recycling graphite are high-temperature calcination and acid leaching precipitation. However, the former will produce a large amount of toxic and harmful gases, polluting the environment, and the latter cannot effectively remove the impurities in graphite by simple acid leaching. The binder, metal oxides and lithium between the graphite layers cannot be completely removed. The layer spacing of the recycled graphite material becomes larger than that of commercial graphite and has a tendency of delamination and shedding, affecting the reuse of recycled graphite and incurring huge time costs.

[0005] Therefore, providing a recycling method for waste graphite to obtain high-performance recycled graphite materials is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0006] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a recycling method of waste graphite, purified graphite and its application.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a recycling method of waste graphite, and the recycling method includes the following steps:

[0009] (1) Mix the composition of acid and hydrogen peroxide with waste graphite, then heat it up for aging to obtain aged graphite.

[0010] (2) Mix the aged graphite with acid solution and perform microwave treatment. Then, mix the mixture after microwave treatment with a promoter and perform high-pressure acid leaching treatment to obtain purified graphite.

[0011] Wherein, the promoter is a mixed organic solution, and the mixed organic solution includes phosphoric acid esters.

[0012] In one embodiment, the waste graphite is the powder obtained by removing the current collector from the graphite negative electrode disassembled from waste lithium-ion batteries, or the powder obtained by removing the current collector from the graphite negative electrode in the ineffective battery cells during the production process, which contains binders.

[0013] In the present invention, the graphite negative electrode means that the active material in the negative electrode includes graphite as the active material. In one embodiment, all the active materials in the negative electrode are graphite.

[0014] In the method of the present invention, by using the composition of acid (such as oxidizing mixed acid) and hydrogen peroxide to age the waste graphite negative electrode, the oxidation reaction of metal elements and oxides inside the waste graphite into salts can be accelerated. At the same time, the aging and decomposition of the binder in the waste graphite negative electrode can also be accelerated. By performing microwave treatment on the aged graphite in acid solution, the microwave reaction can accelerate the dissolution and precipitation of salts and other impurities generated during the aging process, reduce the graphite layer spacing, and restore the graphite structure. At the same time, due to the high-pressure acid leaching treatment of the mixture after microwave treatment under the action of the promoter, the chemical and leaching dissolution kinetic reaction process can be accelerated, the precipitation of impurities can be accelerated, the impurities in the acid leaching process can be reduced, and the graphite layer spacing can be further reduced. The purified graphite prepared by the method of the present invention shows almost no impurity peaks after XRD detection, and the layer spacing is significantly lower than that of the waste graphite. The purified graphite has good electrical conductivity and good electrochemical performance when applied to the negative electrode of lithium-ion batteries.

[0015] In the present invention, if the promoter is not used in the preparation method, or other types of additives are used to replace the promoter of the present invention, it will lead to a decline in the performance of the graphite material, and further lead to a decline in the electrochemical performance of the battery assembled with it.

[0016] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical purpose and beneficial effects of the present invention can be better achieved.

[0017] Preferably, the phosphoric acid ester includes at least one of triethyl phosphate and dimethyl phosphate.

[0018] Preferably, the mixed organic solution further comprises at least one of a ketone and N-methylpyrrolidone;

[0019] Preferably, the mixed organic solution is a mixture of triethyl phosphate and acetone, and the volume ratio of triethyl phosphate to acetone is (1-4):1, such as 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, etc.

[0020] Preferably, the addition amount of the promoter to the mass of the waste graphite is 1:(5-10), such as 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0021] In step (1), the acid in the composition of the acid and hydrogen peroxide comprises at least two of nitric acid, acetic acid, hypochlorous acid, phosphoric acid and citric acid.

[0022] Preferably, in step (1), the acid in the composition of the acid and hydrogen peroxide is a mixed solution of 98wt% concentrated sulfuric acid and 90wt% concentrated hydrochloric acid, wherein the volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid is 2:5-5:2, that is, 0.4-2.5, such as 0.4, 0.6, 1, 1.3, 1.6, 2, 2.2 or 2.5, etc.

[0023] Preferably, in step (1), the mass ratio of the waste graphite to the mass of the composition of the acid and hydrogen peroxide is 50:(20-100), that is, 2.5-0.5, such as 2.5, 2.3, 2, 1.8, 1.5, 1.2, 1, 0.8 or 0.5, etc.

[0024] Preferably, in step (1), the concentration of hydrogen peroxide is 30wt%, and based on the total mass of the acid and the graphite negative electrode being 100%, the mass fraction of hydrogen peroxide is 10-20%, such as 10%, 12%, 14%, 15%, 16%, 18% or 20%, etc.

[0025] Preferably, during the mixing in step (1), stirring is accompanied.

[0026] Preferably, the mixing time in step (1) is 20-60 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc.

[0027] Preferably, in step (1), it is heated to 80-180 °C for aging, and the temperature can be, for example, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C or 180 °C, etc.

[0028] Preferably, in step (1), the aging time is 4 - 32 h, such as 4 h, 6 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h or 32 h, etc.

[0029] Preferably, the aging in step (1) is carried out in a crucible.

[0030] Preferably, the acid solution in step (2) is a mixed solution of a sulfuric acid solution with a concentration of 1 - 3 mol / L -1 (such as 1 mol / L -1 , 1.5 mol / L -1 , mol / L -1 , 2 mol / L -1 , 2.5 mol / L -1 or 3 mol / L -1 etc.) and a hydrochloric acid solution with a concentration of 1 - 3 mol / L -1 (such as 1 mol / L -1 , 1.5 mol / L -1 , mol / L -1 , 2 mol / L -1 , 2.5 mol / L -1 or 3 mol / L -1 etc.). The volume ratio of the sulfuric acid solution to the hydrochloric acid solution is (1 - 3):1, such as 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, etc.

[0031] Preferably, in step (2), the solid - liquid ratio of the aged graphite to the acid solution is 2:1 - 1:10, that is, 2:1 - 0.1:1, such as 2:1, 1.7:1, 1.5:1, 1.2:1, 1:1, 0.8:1, 0.5:1, 0.3:1 or 0.1:1, etc.

[0032] Preferably, in step (2), after mixing the aged graphite with the acid solution, stir for 20 - 40 min and then carry out microwave treatment. The stirring time can be, for example, 20 min, 25 min, 30 min, 35 min or 40 min, etc.

[0033] Preferably, the power of the microwave treatment in step (2) is 50 - 1500 W, such as 50 W, 100 W, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, 900 W, 1000 W, 1100 W, 1200 W, 1300 W, 1400 W or 1500 W, etc.

[0034] Preferably, the number of times of microwave treatment in step (2) is 9 - 12 times, such as 9 times, 10 times, 11 times or 12 times, etc.; the time of each microwave treatment is independently 8 - 15 s, such as 8 s, 9 s, 10 s, 11 s, 12 s, 13 s or 15 s, etc.

[0035] Preferably, the temperature of the high-pressure acid leaching treatment in step (2) is 120 - 200 °C, such as 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or 200 °C, etc.

[0036] Preferably, the time of the high-pressure acid leaching treatment in step (2) is 18 - 33 h, such as 18 h, 20 h, 21 h, 23 h, 25 h, 28 h, 30 h or 32 h, etc.

[0037] In the present invention, the high-pressure acid leaching treatment is carried out in a closed container, and high pressure will be generated when the reactants placed in the container are heated.

[0038] Preferably, after the high-pressure acid leaching treatment in step (2), the product is also subjected to the steps of washing and drying.

[0039] In a second aspect, the present invention provides a purified graphite, which is obtained by the recovery method described in the first aspect.

[0040] In a third aspect, the present invention provides a regenerated graphite, which is prepared by using the purified graphite described in the second aspect.

[0041] In a fourth aspect, the present invention provides a preparation method of the regenerated graphite as described in the third aspect, and the preparation method of the regenerated graphite includes the following steps:

[0042] Mix the purified graphite described in the second aspect and borax, and calcine to obtain the regenerated graphite.

[0043] The present invention uses borax as a regeneration promoter, and utilizes the characteristics of borax sublimating and reducing at high temperature to further remove impurities on the surface of graphite, reduce the oxygen content and impurity content of graphite, and at the same time improve the graphitization degree of graphite, and promote its regeneration to the performance of commercial graphite.

[0044] Preferably, the mass ratio of the purified graphite to the borax is 5:1 - 20:1, such as 5:1, 7:1, 8:1, 10:1, 12:1, 15:1, 17:1, 18:1 or 20:1, etc.

[0045] Preferably, the mixing method of the purified graphite and the borax is grinding and mixing.

[0046] Preferably, the calcination is carried out under the protection of a protective gas.

[0047] Preferably, the protective gas includes at least one of nitrogen, helium and argon.

[0048] Preferably, the calcination temperature is 1600-2000°C, for example, 1600°C, 1650°C, 1700°C, 1750°C, 1800°C, 1900°C, 1950°C or 2000°C.

[0049] Preferably, the calcination time is 2-4 h, for example, 2 h, 2.2 h, 2.5 h, 3 h, 3.3 h, 3.6 h or 4 h.

[0050] The interlayer spacing of the regenerated graphite of the present invention is substantially the same as that of commercial graphite, and is significantly lower than that of purified graphite. Moreover, compared with purified graphite, the graphitization degree of the regenerated graphite is improved, the conductivity is improved, and the impurity content is reduced. Therefore, the electrochemical performance of the battery using the regenerated graphite is further improved compared with purified graphite.

[0051] In a fifth aspect, the present invention provides a negative electrode, wherein the negative electrode comprises the regenerated graphite described in the third aspect.

[0052] In a sixth aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the negative electrode described in the fifth aspect.

[0053] The numerical range described in the present invention not only includes the point values listed above, but also includes any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) In the method of the present invention, by using a composition of an acid (for example, an oxidizing mixed acid) and hydrogen peroxide to ripen the waste graphite negative electrode, the oxidation salt reaction of the metal element and the oxide inside the waste graphite can be accelerated, and at the same time, the aging and decomposition of the binder in the waste graphite negative electrode can also be accelerated. By subjecting the ripened graphite to microwave treatment in an acid solution, the microwave reaction can accelerate the dissolution and precipitation of impurities such as salts generated during the ripening process, reduce the graphite interlayer spacing, and restore the graphite structure. At the same time, since the mixed solution after microwave treatment is subjected to high-pressure acid leaching treatment under the action of a promoter, the chemical and leaching and dissolution kinetic reaction processes can be accelerated, the precipitation of impurities can be accelerated, the impurities in the acid leaching process can be reduced, and the graphite interlayer spacing can be further reduced. The purified graphite prepared by the method of the present invention is tested by XRD and shows that the impurity peaks are almost gone, and the interlayer spacing is significantly reduced compared to the interlayer spacing of the waste graphite. The purified graphite has good conductivity and has good electrochemical properties when applied to the negative electrode of a lithium ion battery.

[0056] (2) The interlayer spacing of the regenerated graphite of the present invention is basically the same as that of commercial graphite, and is significantly lower than that of purified graphite. Moreover, compared with purified graphite, the graphitization degree of regenerated graphite is improved, the conductivity is increased, and the impurity content is reduced. Therefore, when regenerated graphite is used in batteries, its electrochemical performance is further improved compared with purified graphite. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a SEM image of waste graphite.

[0058] Figure 2 It is a diagram showing the influence of different volume ratios of acid in the mixed acid on impurity removal in the ripening step.

[0059] Figure 3 It is a diagram showing the influence of different mass ratios (i.e., solid-liquid ratio) of waste graphite and mixed acid on impurity removal.

[0060] Figure 4 It is a diagram showing the influence of different proportions of H2O2 solution on impurity removal.

[0061] Figure 5 It is a diagram comparing the element contents in graphite before and after microwave reaction in Example 1.

[0062] Figure 6 It is a diagram showing the influence of different acid leaching times on impurity removal.

[0063] Figure 7 It is a diagram showing the influence of different acid leaching temperatures on impurity removal.

[0064] Figure 8 It is a SEM image of the purified graphite prepared in Example 1

[0065] Figure 9 It is an XRD diagram of the purified graphite and regenerated graphite prepared in Example 1.

[0066] Figure 10 It is a Raman spectrum of the waste graphite, purified graphite and regenerated graphite in Example 1.

[0067] Figure 11 It is the cycle performance curves of Application Example 1-A, Application Example 1-B, Application Comparative Example 1 and Application Comparative Example 2. Among them, the negative electrode material in Application Example 1-A is the purified graphite in Example 1, the negative electrode material in Application Example 1-B is the regenerated graphite in Example 1, the negative electrode material in Application Comparative Example 1 is waste graphite, and the negative electrode material in Application Comparative Example 2 is commercial graphite. DETAILED DESCRIPTION OF THE INVENTION

[0068] The technical solution of the present invention will be further described below in conjunction with the drawings and through specific embodiments.

[0069] In the embodiments of the present invention, the ternary waste battery cell refers to that the positive active material in the battery cell is ternary material.

[0070] In the embodiments of the present invention, the solid-liquid mixture in step (1) refers to the mixture of the mixed acid and the negative electrode plate in step (1).

[0071] Example 1

[0072] A method for recycling waste graphite includes the following steps:

[0073] (1) Aging of waste graphite

[0074] Take the negative electrode plate disassembled from the ternary waste battery cell with 0% SOH, scrape the active layer from the negative electrode plate off the current collector to obtain 50 g of waste graphite powder. Place the waste graphite in a polytetrafluoroethylene container, and use 100 g of mixed acid (a mixed solution of concentrated sulfuric acid with a mass concentration of 98 wt% and concentrated hydrochloric acid with a mass concentration of 90 wt%, and the volume ratio of the two satisfies V 硫酸 :V 盐酸 = 1.2:1) and H2O2 solution (with a mass concentration of 30 wt%) accounting for 20% of the mass of the solid-liquid mixture for mixing and stirring for 30 min. Place the graphite mixture in a corundum crucible and age it at 150 °C for 25 h to fully react and dissolve the metals and metal oxides inside the graphite to obtain aged graphite.

[0075] In step (1) of this example, the mass ratio of the waste graphite to the mixed acid (i.e., the solid-liquid ratio) is 0.5.

[0076] (2) Preparation of purified graphite

[0077] Take the aged graphite and the acid solution (a mixed solution of H2SO4 solution with a concentration of 2 mol L -1 and HCl solution with a concentration of 1 mol L -1 , and the volume ratio of the two satisfies V 硫酸 :V 盐酸 = 2:1) and mix them according to the solid-liquid ratio of 1:1 to obtain a solid-liquid mixture. Stir the solid-liquid mixture for 30 min, use a microwave reactor to carry out microwave reaction on the mixture, set the power to 1000 W, and carry out microwave reaction 10 times, with each reaction time being 10 s. Place the mixture after microwave reaction in a high-pressure reactor, add 6.25 g of accelerator (a mixed organic solution with a volume ratio of triethyl phosphate to acetone of 2:1), carry out acid leaching at 140 °C for 24 h, take out the graphite, wash it with deionized water until neutral, and dry it in a vacuum oven at 80 °C to obtain purified graphite.

[0078] In the mixed acid used in step (1) of this example, V 硫酸 :V 盐酸= 1.2:1.

[0079] Figure 1 It is the SEM image of waste graphite. Figure 8 It is the SEM image of purified graphite. SEM analysis shows that through aging and acid leaching, the binders and metal impurities inside the material are effectively removed. The purified graphite material basically presents a purified graphite state, and the surface of the purified graphite is smoother than that of the waste graphite.

[0080] ICP detection was carried out on the graphite before and after the microwave reaction to obtain the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements in it. The results are shown in Figure 5 . It can be seen from the figure that the microwave reaction in the present invention has a significant effect on the impurity removal effect, and the microwave reaction is beneficial to the removal of impurities.

[0081] ICP detection was carried out on the purified graphite to obtain the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements in it. The results are shown in Figure 2 .

[0082] A regenerated graphite, the preparation method thereof comprises the following steps:

[0083] Take the above-mentioned purified graphite and borax according to a mass ratio of 10:1 for sampling, and fully grind and mix them in an agate mortar to obtain a graphite and borax mixture. Place this mixture in a corundum crucible, and place the corundum crucible containing the mixture in a high-temperature tubular furnace. Bake at 1800 °C for 3 h under an argon atmosphere to obtain regenerated graphite.

[0084] Figure 9 It is the XRD pattern of the purified graphite and regenerated graphite prepared in this example. Through XRD analysis and calculation using the Bragg equation (nλ = 2dsinθ), it shows that the layer spacing of the purified graphite is significantly reduced compared with that of the waste graphite and the impurity peaks almost disappear. However, the layer spacing is still higher than that of commercial graphite. This indicates that through the two processes of aging and acid leaching, the graphite impurities are basically removed. At the same time, the use of a promoter and microwave reaction has an obvious effect on reducing the impurity content and reducing the layer spacing. The layer spacing of the regenerated graphite is basically the same as that of commercial graphite and is significantly reduced compared with that of the purified graphite, indicating that the method of using borax and high-temperature regeneration has an obvious effect on reducing graphite impurities, improving the graphitization degree of graphite, and promoting graphite normalization.

[0085] Figure 10 It is the Raman spectrum of the waste graphite, purified graphite, and regenerated graphite in this example. The results show that through purification and regeneration, the graphitization degree of graphite is further improved, indicating that aging, acid leaching, and high-temperature regeneration play a key promoting role in graphite regeneration.

[0086] Example 2

[0087] A method for recycling waste graphite comprises the following steps:

[0088] (1) Aging of waste graphite

[0089] Take the negative electrode sheet disassembled from the 0% SOH ternary waste battery cell, scrape the active layer from the negative electrode sheet from the current collector to obtain 50g of waste graphite powder, put the waste graphite in a polytetrafluoroethylene container, use 70g of mixed acid (a mixed solution of concentrated sulfuric acid with a mass concentration of 98wt% and concentrated hydrochloric acid with a mass concentration of 90wt%, and the volume ratio of the two meets V 硫酸 :V 盐酸 =2:1) and H2O2 solution (mass concentration is 30wt%) accounting for 15% of the mass of the solid-liquid mixture are mixed and stirred for 50 minutes, and the graphite mixture is placed in a corundum crucible and aged for 10 hours at 110°C to allow the metal and metal oxide inside the graphite to fully react and dissolve, thereby obtaining aged graphite;

[0090] (2) Preparation of purified graphite

[0091] Take the matured graphite and acid solution (concentration 1 mol L -1 H2SO4 solution and a concentration of 1.5 mol L -1 The volume ratio of the mixed solution of HCl solution satisfies V 硫酸 :V 盐酸 =1:1) were mixed according to a solid-liquid ratio of 1:5 to obtain a solid-liquid mixture, the solid-liquid mixture was stirred for 20 min, the mixture was subjected to microwave reaction using a microwave reactor, the power was set to 700 W, the microwave reaction was performed 12 times, and the reaction time for each time was 8 s, the mixture after the microwave reaction was placed in a high-pressure reactor, 5 g of a promoter (a mixed organic solution of triethyl phosphate and acetone with a volume ratio of 3:1) was added, and acid leaching was performed at 130 ° C for 18 h, the graphite was taken out, washed with deionized water until neutral, and dried in a vacuum oven at 90 ° C to obtain purified graphite.

[0092] A regenerated graphite, the preparation method of which comprises the following steps:

[0093] The purified graphite and borax after acid leaching, cleaning and drying were sampled in a mass ratio of 15:1, and were fully ground and mixed in an agate mortar to obtain a mixture of graphite and borax. The mixture was placed in a corundum crucible, and the corundum crucible containing the mixture was placed in a high-temperature tube furnace, and calcined at 2000°C for 2h in an argon atmosphere to obtain regenerated graphite.

[0094] Example 3

[0095] A method for recycling waste graphite comprises the following steps:

[0096] (1) Aging of waste graphite

[0097] Take the negative electrode sheet disassembled from the 0% SOH ternary waste battery cell, scrape the active layer from the current collector on the negative electrode sheet to obtain 50g of waste graphite powder, put the waste graphite in a polytetrafluoroethylene container, use 30g of mixed acid (a mixed solution of concentrated sulfuric acid with a mass concentration of 98wt% and concentrated hydrochloric acid with a mass concentration of 90wt%, and the volume ratio of the two meets V 硫酸 :V 盐酸 =2.5:1) and H2O2 solution (mass concentration is 30wt%) accounting for 10% of the mass of the solid-liquid mixture are mixed and stirred for 20 minutes, and the graphite mixture is placed in a corundum crucible and aged for 6 hours at 170°C to allow the metal and metal oxide inside the graphite to fully react and dissolve to obtain aged graphite;

[0098] (2) Preparation of purified graphite

[0099] Take the matured graphite and acid solution (concentration 3 mol L -1 The H2SO4 solution and the concentration are 2 mol L -1 The volume ratio of the mixed solution of HCl solution satisfies V 硫酸 :V 盐酸 =2.5:1) were mixed according to a solid-liquid ratio of 1:7 to obtain a solid-liquid mixture, the solid-liquid mixture was stirred for 40 min, the mixture was subjected to microwave reaction using a microwave reactor, the power was set to 1250 W, the microwave reaction was performed 9 times, and the reaction time for each time was 15 s, the mixture after the microwave reaction was placed in a high-pressure reactor, 10 g of a promoter (a mixed organic solution of triethyl phosphate and acetone with a volume ratio of 2.5:1) was added, and acid leaching was carried out at 180 ° C for 30 h, the graphite was taken out, washed with deionized water until neutral, and dried in a vacuum oven at 80 ° C to obtain purified graphite.

[0100] A regenerated graphite, the preparation method of which comprises the following steps:

[0101] The purified graphite and borax were sampled in a mass ratio of 7:1, and were fully ground and mixed in an agate mortar to obtain a mixture of graphite and borax. The mixture was placed in a corundum crucible, and the corundum crucible containing the mixture was placed in a high-temperature tube furnace, and calcined at 1650° C. for 4 h in an argon atmosphere to obtain regenerated graphite.

[0102] Embodiment 4-7

[0103] A method for recycling waste graphite, which differs from Example 1 in that, in the mixed acid used in step (1), V 硫酸 :V 盐酸 They are 0.4, 0.8, 2 and 2.5 respectively.

[0104] A regenerated graphite, the difference in its preparation method from that of Example 1 lies in that the purified graphite obtained by preparing Examples 4-7 is respectively used to replace the purified graphite obtained by preparing Example 1.

[0105] According to the same method as in Example 1, ICP detection was carried out on the purified graphite obtained by preparing Examples 4-7, and the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements therein were obtained. The results are shown in Figure 2 .

[0106] It can be seen from Figure 2 that when V 硫酸 : V 盐酸 is within the range of 0.4 - 2.5, a good impurity removal effect can be achieved, and this V 硫酸 : V 盐酸 has a greater influence on the impurity removal effect of cobalt ions. When V 硫酸 : V 盐酸 is 0.8 - 2, the comprehensive impurity removal effect of various elements is better.

[0107] Examples 8 - 11

[0108] A method for recycling waste graphite, the difference from Example 1 lies in that in step (1), the mass ratio of waste graphite to mixed acid (i.e., solid-liquid ratio) is 1, 1.5, 2, and 2.5 respectively.

[0109] A regenerated graphite, the difference in its preparation method from that of Example 1 lies in that the purified graphite obtained by preparing Examples 4-7 is respectively used to replace the purified graphite obtained by preparing Example 1.

[0110] According to the same method as in Example 1, ICP detection was carried out on the purified graphite obtained by preparing Examples 8-11, and the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements therein were obtained. The results are shown in Figure 3 .

[0111] It can be seen from Figure 3 that during the aging process, when the mass ratio of waste graphite to mixed acid (i.e., solid-liquid ratio) is within the range of 2.5 - 0.5, the overall trend of the impurity removal effect gets better as the solid-liquid ratio decreases, and cobalt element is greatly affected by this solid-liquid ratio. When the solid-liquid ratio is within the range of 1.5 - 0.5, the comprehensive impurity removal effect for various elements is better.

[0112] Examples 12 - 15

[0113] A method for recycling waste graphite, the difference from Example 1 lies in that in step (1), the mass fraction of H2O2 solution is 10%, 15%, 25%, and 30%.

[0114] A regenerated graphite, the difference in its preparation method from that of Example 1 lies in that the purified graphite prepared in Examples 12 - 15 is respectively used to replace the purified graphite prepared in Example 1.

[0115] ICP detection was carried out on the purified graphite prepared in Examples 8 - 11 according to the same method as in Example 1, and the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements in it were obtained. The results are shown in Figure 4 .

[0116] It can be seen from Figure 4 that when the proportion of hydrogen peroxide is in the range of 10 - 25%, the impurity removal effect is better. When the hydrogen peroxide increases to 30%, it is instead not conducive to impurity removal.

[0117] Examples 16 - 20

[0118] A method for recycling waste graphite, the difference from Example 1 lies in that the acid leaching time in step (2) is 18h, 21h, 27h, 30h, and 33h respectively.

[0119] A regenerated graphite, the difference in its preparation method from that of Example 1 lies in that the purified graphite prepared in Examples 16 - 20 is respectively used to replace the purified graphite prepared in Example 1.

[0120] ICP detection was carried out on the purified graphite prepared in Examples 16 - 20 according to the same method as in Example 1, and the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements in it were obtained. The results are shown in Figure 6 .

[0121] It can be seen from Figure 6 that with the extension of the acid leaching time, it is beneficial to the removal of impurities. It is preferably when the acid leaching time is 24 - 33h that the impurity removal effect is better.

[0122] Examples 21 - 23

[0123] A method for recycling waste graphite, the difference from Example 1 lies in that the acid leaching temperatures in step (2) are 120°C, 180°C, and 200°C respectively.

[0124] A regenerated graphite, the difference in its preparation method from that of Example 1 lies in that the purified graphite prepared in Examples 16 - 20 is respectively used to replace the purified graphite prepared in Example 1.

[0125] ICP detection was carried out on the purified graphite prepared in Examples 21 - 23 according to the same method as in Example 1, and the contents of Li, Al, Co, Cu, Ni, Fe, and Mn elements in it were obtained. The results are shown in Figure 7 .

[0126] It can be seen fromFigure 7 It can be seen that when the acid leaching temperature is 120 - 200 °C, it is beneficial to impurity removal, and preferably at 130 - 200 °C, better impurity removal effect can be obtained.

[0127] Application Example 1 - A

[0128] A battery includes a positive electrode, a negative electrode, a separator and an electrolyte. The preparation method of the battery includes the following steps:

[0129] (1) Prepare the positive electrode: According to the mass ratio of 96:1.5:1.5:1:40, mix LiFePO4, PVDF, SP, carbon nanotubes (CNTs) and NMP to make a slurry, coat it on the aluminum foil, and obtain the positive electrode sheet after drying.

[0130] (2) Prepare the negative electrode: According to the mass ratio of 95:2.5:1.5:1:150, mix the negative electrode material (which can be used graphite, purified graphite or recycled graphite, for example), CMC, SBR, SP and H2O to obtain the negative electrode sheet.

[0131] (3) The electrolyte uses LiPF6 / EC + DEC (LiPF6 is the electrolyte, and the mixture of EC and DEC with a volume ratio of 1:1 is the solvent, and the electrolyte concentration is 1.3 mol / L); the separator uses a composite film of polyethylene PE, polypropylene PP and polyethylene - propylene PEP. The assembly of the button cell is carried out in a glove box filled with argon.

[0132] Assemble the battery using the positive electrode, negative electrode, separator and electrolyte.

[0133] In this Application Example 1, the negative electrode material is the purified graphite in Example 1.

[0134] Application Example 1 - B

[0135] A battery, the difference from Application Example 1 - A is only that in the preparation process of the battery, the negative electrode material uses the recycled graphite in Example 1 to replace the purified graphite in Example 1.

[0136] Application Example 2 - 23

[0137] A battery, the difference from Application Example 1 - A is only that in the preparation process of the battery, the negative electrode material uses the recycled graphite in Example 2 - 23 to replace the purified graphite in Example 1.

[0138] Application Comparative Example 1

[0139] A battery, the difference from Application Example 1 - A is only that in the preparation process of the battery, the negative electrode material uses the used graphite in Example 1 to replace the purified graphite in Example 1.

[0140] Application Comparative Example 2

[0141] A battery, which is only different from Application Example 1-A in that during the preparation process of the battery, commercial graphite is used as the negative electrode material to replace the purified graphite in Example 1.

[0142] Performance test:

[0143] The batteries of Application Example 1-A, Application Example 1-B, Application Example 2-23, Application Comparative Example 1 and Application Comparative Example 2 were subjected to a cycle performance test. The charge rate and discharge rate were both 1 / 3C, and the number of cycles was 50 times. The initial Coulombic efficiency, the discharge capacity after 50 cycles and the cycle capacity retention rate were recorded. The results are shown in Table 1.

[0144] The cycle performance curves of Application Example 1-A, Application Example 1-B, Application Comparative Example 1 and Application Comparative Example 2 are as Figure 11 shown. It can be seen from the figure that the cycle performance of the lithium-ion battery assembled with the purified graphite prepared by the aging method and acid leaching method in the present invention has been greatly improved compared with waste graphite. On this basis, the cycle performance of the lithium-ion battery assembled with the regenerated graphite prepared by the high-temperature regeneration method is further improved and is comparable to that of the lithium-ion battery assembled with commercial graphite. The specific capacity after 50 cycles at 0.1C is 349 mAh g -1 , and the initial Coulombic efficiency is 91.3%. It can be shown that the graphitization degree and the cycle stability of the material have been greatly improved after borax impurity removal and high-temperature regeneration.

[0145] Table 1

[0146]

[0147]

[0148] As can be seen from Table 1, the lithium-ion battery assembled with the purified graphite prepared by the method of the present invention has good electrochemical performance, and the electrochemical performance of the lithium-ion battery assembled with the regenerated graphite further obtained by high-temperature regeneration of the purified graphite is further improved and can reach the level of commercial graphite. The initial Coulombic efficiency of the batteries of Application Example 1-B, Application Example 2 and Application Example 3 is above 91%, and the cycle capacity retention rate is above 93.5%. The content of impurities in the graphite of the batteries of the remaining Application Example 2-23 is slightly lower than that of Application Example 1-B, and they still have good electrochemical performance. The method of the present invention and the graphite material prepared by using it have good application prospects. However, the electrochemical performance of the lithium-ion battery assembled with waste graphite is poor and cannot meet the actual application requirements.

[0149] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the present invention's product, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for recycling waste graphite, characterized in that, The recycling method comprises the following steps: (1) After mixing a composition of an acid and hydrogen peroxide with waste graphite, heating is carried out for ripening to obtain ripened graphite; (2) After mixing the ripened graphite with an acid solution and carrying out microwave treatment, mixing the mixture after microwave treatment with a promoter and carrying out high-pressure acid leaching treatment to obtain purified graphite; After mixing the ripened graphite with the acid solution, stirring is carried out for 20 - 40 min and then microwave treatment is carried out; The number of times of the microwave treatment is 9 - 12 times, and the time of each microwave treatment is independently 8 - 15 s; The addition amount of the promoter and the mass ratio of the waste graphite is 1:(5 - 10); Wherein, the promoter is a mixed organic solution, and the mixed organic solution includes phosphate ester.

2. The recycling method of waste graphite according to claim 1, wherein The phosphate ester includes at least one of triethyl phosphate and dimethyl phosphate.

3. The recycling method of waste graphite according to claim 1, wherein, The mixed organic solution further includes at least one of a ketone and N-methylpyrrolidone.

4. The recycling method of waste graphite according to claim 1, characterized in that, The mixed organic solution is a mixture of triethyl phosphate and acetone, and the volume ratio of triethyl phosphate to acetone is (1 - 4):

1.

5. The recycling method of waste graphite according to claim 1, characterized in that, In step (1), the acid in the composition of the acid and hydrogen peroxide includes at least two of nitric acid, acetic acid, hypochlorous acid, phosphoric acid and citric acid.

6. The recycling method of waste graphite according to claim 1, wherein In step (1), the acid in the composition of the acid and hydrogen peroxide is a mixed solution of 98 wt% concentrated sulfuric acid and 90 wt% concentrated hydrochloric acid, wherein the volume ratio of concentrated sulfuric acid to concentrated hydrochloric acid is 2:5 - 5:

2.

7. The recycling method of waste graphite according to claim 1, characterized in that, In step (1), the mass ratio of the waste graphite to the mass of the composition of the acid and hydrogen peroxide is 50:(20 - 100).

8. The recycling method of waste graphite according to claim 1, characterized in that, In step (1), the concentration of the hydrogen peroxide is 30 wt%, and based on the total mass of the acid and the waste graphite being 100%, the mass proportion of the hydrogen peroxide is 10 - 20%.

9. The recycling method of waste graphite according to claim 1, characterized in that, During the mixing process in step (1), stirring is accompanied.

10. The recycling method of waste graphite according to claim 1, wherein The mixing time in step (1) is 20 - 60 min.

11. The recycling method of waste graphite according to claim 1, wherein, In step (1), heating is carried out to 80 - 180 °C for ripening.

12. The recycling method of waste graphite according to claim 1, wherein, In step (1), the ripening time is 4 - 32 h.

13. The recycling method of waste graphite according to claim 1, characterized in that, The ripening in step (1) is carried out in a crucible.

14. The recycling method of waste graphite according to claim 1, characterized in that, The acid solution described in step (2) is a mixed solution of a sulfuric acid solution with a concentration of 1 - 3 mol / L -1 and a hydrochloric acid solution with a concentration of 1 - 3 mol / L -1 , and the volume ratio of the sulfuric acid solution to the hydrochloric acid solution is (1 - 3):

1.

15. The recycling method of waste graphite according to claim 1, characterized in that In step (2), the solid-liquid ratio of the ripened graphite and the acid solution is 2:1 - 1:

10.

16. The recycling method of waste graphite according to claim 1, characterized in that, The power of the microwave treatment in step (2) is 50 - 1500 W.

17. The recycling method of waste graphite according to claim 1, wherein, The temperature of the high-pressure acid leaching treatment in step (2) is 120 - 200 °C.

18. The recycling method of waste graphite according to claim 1, characterized in that, The time of the high-pressure acid leaching treatment in step (2) is 18 - 33 h.

19. The recycling method of waste graphite according to claim 1, characterized in that, After the high-pressure acid leaching treatment in step (2), steps of washing and drying the product are further carried out.

20. A purified graphite, characterized in that, The purified graphite is obtained by the recycling method according to any one of claims 1 - 19.

21. A regenerated graphite, characterized in that, The regenerated graphite is prepared by using the purified graphite according to claim 20.

22. A method for preparing regenerated graphite as described in claim 21, characterized in that, The preparation method of the regenerated graphite comprises the following steps: Mixing the purified graphite according to claim 20 and borax, and roasting to obtain the regenerated graphite.

23. The method for preparing regenerated graphite according to claim 22, characterized in that, The mass ratio of the purified graphite to the borax is 5:1 - 20:

1.

24. The method for preparing regenerated graphite according to claim 22, wherein The mixing method of the purified graphite and the borax is grinding and mixing.

25. The method for preparing regenerated graphite according to claim 22, wherein The roasting is carried out under the protection of a protective gas.

26. The method for preparing regenerated graphite according to claim 25, wherein, The protective gas includes at least one of nitrogen, helium and argon.

27. The method for preparing regenerated graphite according to claim 22, characterized in that, The temperature of the roasting is 1600 - 2000 °C.

28. The method for preparing regenerated graphite according to claim 22, characterized in that, The time of the roasting is 2 - 4 h.

29. A negative electrode, characterized in that, The negative electrode includes the recycled graphite described in claim 21.

30. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode described in claim 29.

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