Nano calcium silicate hydrate modified waste graphite negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a nano calcium silicate hydrate modified waste graphite negative electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing waste graphite powder, soluble calcium salt, soluble silicate and water for reaction, and then drying to obtain nano calcium silicate hydrate modified waste graphite powder; and calcining the nano calcium silicate hydrate modified waste graphite powder to obtain the nano calcium silicate hydrate modified waste graphite negative electrode material. According to the method, the nano-scale hydrated calcium silicate gel is generated on the surface of the waste graphite in situ to coat the surface of the waste graphite, so that surface defects caused by various aging mechanisms in the long-time use process of the waste graphite can be repaired, and the charge-discharge performance and the cycle performance of the waste graphite are remarkably improved. The process flow is simple, the reaction condition is mild, acid and alkali washing is not needed, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials, and in particular relates to a nano-calcium silicate hydrate modified waste graphite negative electrode material, a preparation method and an application thereof. Background Art

[0002] Compared to other batteries, lithium-ion batteries offer advantages such as high energy density, long lifespan, compact size, and light weight. They are now widely used in various fields, resulting in a large amount of discarded lithium-ion batteries. Graphite, the primary anode material in lithium-ion batteries, is abundant and has a single component. Incineration can also cause significant environmental pollution. Therefore, recycling discarded graphite can not only effectively reduce the cost of lithium-ion batteries but also effectively reduce environmental pollution.

[0003] Currently, the most common recycling method for waste graphite is to soak it in strong acids or bases, followed by high-temperature heat treatment to remove organic matter from the waste graphite and repair its aged structure. However, soaking with high concentrations of strong acids and bases is costly and requires extreme reaction conditions due to the large amounts of acid and base used.

[0004] Therefore, how to simply, gently and cost-effectively utilize waste graphite to prepare graphite negative electrode materials with excellent performance is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies, propose a nano-calcium silicate hydrate modified waste graphite negative electrode material and its preparation method and application, and solve the technical problems of high cost and extreme reaction conditions when using strong acid or strong base to soak waste graphite in the existing technology.

[0006] In a first aspect, the present invention provides a method for preparing a waste graphite negative electrode material modified with nano-calcium silicate hydrate, comprising the following steps: Waste graphite powder, soluble calcium salt, soluble silicate and water are mixed and reacted, and then dried to obtain nano-hydrated calcium silicate modified waste graphite powder; The waste graphite powder modified by nanometer calcium silicate hydrate is calcined to obtain the waste graphite negative electrode material modified by nanometer calcium silicate hydrate.

[0007] In a second aspect, the present invention provides a nano-calcium silicate hydrate modified waste graphite negative electrode material, which is obtained by the preparation method of the nano-calcium silicate hydrate modified waste graphite negative electrode material provided by the first aspect of the present invention.

[0008] In a third aspect, the present invention provides an application of a waste graphite negative electrode material modified by nano-calcium silicate hydrate, and the waste graphite negative electrode material modified by nano-calcium silicate hydrate is applied to a lithium battery.

[0009] Compared with the prior art, the present invention has the following beneficial effects: This method coats the waste graphite by in-situ generating a nanoscale calcium silicate hydrate gel on its surface. This method can repair surface defects caused by various aging mechanisms during long-term use, significantly improving the charge-discharge and cycling performance of the waste graphite. The process is simple, the reaction conditions are mild, and no acid or alkali washing is required, reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a scanning electron microscope image of the waste graphite powder used in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the waste graphite powder modified with nano-calcium silicate hydrate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0012] In a first aspect, the present invention provides a method for preparing a waste graphite negative electrode material modified with nano-calcium silicate hydrate, comprising the following steps: S1, mixing waste graphite powder, soluble calcium salt, soluble silicate and water for reaction, and then drying to obtain nano-hydrated calcium silicate modified waste graphite powder; S2. calcining the nano-calcium silicate hydrate modified waste graphite powder to obtain the nano-calcium silicate hydrate modified waste graphite negative electrode material.

[0013] The present invention increases the specific surface area of ​​waste graphite when used as a negative electrode material for (lithium) batteries by composite modification of waste graphite with calcium silicate hydrate, thereby improving the diffusion efficiency of (lithium) ions. The layered structure of calcium silicate hydrate allows lithium ions to be embedded between layers, repairing the aged surface structure of waste graphite. At the same time, the surface of calcium silicate hydrate is rich in hydroxyl (-OH) and siloxy (Si-O -) increases the active sites for electrochemical reactions, and the synergistic effect of graphite and hydrated calcium silicate makes the coated composite material have a larger theoretical capacity. At the same time, the nanoporous structure of hydrated calcium silicate can buffer the volume expansion of graphite when lithium is inserted, and has better structural stability. Calcium silicate hydrate gel is a porous material. Its coating on the surface of waste graphite not only does not affect its charge transfer during use, but the protective effect brought by the coating also significantly improves the discharge specific capacity of the waste graphite after multiple charge and discharge cycles. The present invention avoids the generation of wastewater and waste of raw materials by directly drying the reaction product; the present invention can purify the graphite and remove excess water by calcination, avoiding the reaction of residual water with lithium hexafluorophosphate or lithium metal in the electrolyte to produce expansion, corrode the electrode material, and cause a sharp drop in capacity and safety risks. The process flow of the present invention is simple, the reaction conditions are mild, the processing cost is low, the stability is excellent, and it has a high cost performance.

[0014] In this embodiment, in step S1, the waste graphite powder is obtained by discharging, disassembling, grinding and sieving waste batteries.

[0015] In this embodiment, in step S1, the particle size of the waste graphite powder is below 200 mesh, including but not limited to 200 mesh, 300 mesh, 400 mesh, 500 mesh, etc.

[0016] In this embodiment, in step S1, the soluble calcium salt is at least one of calcium chloride, calcium nitrate, calcium formate, calcium acetate, calcium bicarbonate and calcium gluconate.

[0017] In this embodiment, in step S1, the soluble silicate is at least one of sodium silicate, sodium fluorosilicate, potassium silicate and lithium silicate.

[0018] In this embodiment, in step S1, the molar ratio of calcium in the soluble calcium salt to silicon in the soluble silicate is (0.5-3.0):1, preferably (0.9-1.1):1, and more preferably 1:1. If the soluble calcium salt accounts for too much, it will result in excessive free calcium remaining in the synthesized calcium silicate hydrate, affecting the overall morphology and conductivity after drying. If the soluble silicate accounts for too much, it will affect the structure of the calcium silicate hydrate, resulting in poor repair results.

[0019] In this embodiment, in step S1, the mass ratio of the waste graphite powder to the theoretical content of calcium silicate hydrate is 1:(0.05-0.4), preferably 1:(0.1-0.2). It should be noted that the theoretical content of calcium silicate hydrate refers to the theoretical amount of calcium silicate that can be formed by the reaction of calcium in soluble calcium salts with soluble silicates. A too low theoretical content of calcium silicate hydrate will result in a poor repair effect. A too high theoretical content of calcium silicate hydrate will result in a low proportion of graphite in the negative electrode material, which in turn reduces conductivity.

[0020] In this embodiment, in step S1, the mass ratio of waste graphite powder to water is 1:(0.5-3), preferably 1:(0.6-1.3). By controlling the mass ratio of waste graphite powder to water within the above range, the generation of wastewater can be reduced while ensuring sufficient reaction, thereby reducing the energy consumption required for the drying process.

[0021] In this embodiment, in step S1, the particle size of the waste graphite powder modified by nano-calcium silicate hydrate is below 200 mesh, including but not limited to 200 mesh, 300 mesh, 400 mesh, 500 mesh, etc.

[0022] In this embodiment, step S1 includes: S11, preparing a soluble calcium salt solution and a soluble silicate solution; S12, mixing the waste graphite powder, the soluble calcium salt solution, and the soluble silicate solution, and then drying, grinding, and sieving to obtain nano-hydrated calcium silicate-modified waste graphite powder.

[0023] Specifically, in step S11, the mass fraction of the soluble calcium salt solution is 10 wt% to 40 wt%.

[0024] Specifically, in step S11, the mass fraction of the soluble silicate solution is 10 wt% to 30 wt%.

[0025] Specifically, in step S12, the waste graphite powder, the soluble calcium salt solution and the soluble silicate solution are mixed and reacted by adding the soluble calcium salt solution and the soluble silicate solution to the waste graphite powder at the same time and performing a mixing reaction.

[0026] Specifically, in step S12, the mesh size of the sieve is ≥200 mesh, including but not limited to 200 mesh, 300 mesh, 400 mesh, 500 mesh, etc.

[0027] In this embodiment, in step S1, the temperature of the mixing reaction is 20-80° C., preferably 20-30° C., and the time of the mixing reaction is 4-12 h.

[0028] In this embodiment, in step S2, the calcination temperature is 300-800°C, the calcination time is 1-5 hours, the heating rate is 2-5°C / min, and the calcination is performed under a protective atmosphere.

[0029] In a second aspect, the present invention provides a nano-calcium silicate hydrate modified waste graphite negative electrode material, which is obtained by the preparation method of the nano-calcium silicate hydrate modified waste graphite negative electrode material provided by the first aspect of the present invention.

[0030] In a third aspect, the present invention provides an application of a waste graphite negative electrode material modified by nano-calcium silicate hydrate, and the waste graphite negative electrode material modified by nano-calcium silicate hydrate is applied to a lithium battery.

[0031] Example 1 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 1.59 g of 30 wt% calcium chloride solution and 2.63 g of 20 wt% sodium silicate solution were added to 5 g of waste graphite powder, and the mixture was mixed and reacted at 25 °C for 4 h. The reaction product was then dried and ground into powder, and passed through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0032] Example 2 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 3.18 g of 30 wt% calcium chloride solution and 5.26 g of 20 wt% sodium silicate solution were added to 5 g of waste graphite powder, and the mixture was mixed and reacted at 25 °C for 12 h. The reaction product was then dried and ground into powder, and passed through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0033] Example 3 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 1.59 g of 15 wt% calcium chloride solution and 2.63 g of 10 wt% sodium silicate solution were added to 5 g of waste graphite powder, and the mixture was mixed and reacted at 25 °C for 4 h. The reaction product was then dried and ground into powder, and passed through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0034] Example 4 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) Add 6.36 g of 30 wt% calcium chloride solution and 10.52 g of 20 wt% sodium silicate solution to 5 g of waste graphite powder, and mix and react at 25 °C for 4 h. Then, dry and grind the reaction product into powder, and pass it through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0035] Example 5 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 4.77 g of 30 wt% calcium chloride solution and 2.63 g of 20 wt% sodium silicate solution were added to 5 g of waste graphite powder, and the mixture was mixed and reacted at 25 °C for 4 h. The reaction product was then dried and ground into powder, and passed through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0036] Example 6 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 1.59 g of 30 wt% calcium chloride solution and 5.26 g of 20 wt% sodium silicate solution were added to 5 g of waste graphite powder, and the mixture was mixed and reacted at 25 °C for 4 h. The reaction product was then dried and ground into powder, and passed through a 200 mesh sieve to obtain nano-hydrated calcium silicate modified waste graphite powder; (3) The waste graphite powder modified with nano-calcium silicate hydrate was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain the waste graphite negative electrode material modified with nano-calcium silicate hydrate.

[0037] Comparative Example 1 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) 5 g of waste graphite powder and 50 g of 1 M concentrated hydrochloric acid were added to a reaction vessel, and the mixture was mixed and reacted at a constant temperature of 60 ° C for 12 h. The reaction product was separated into solid and liquid, and then washed with deionized water, dried, ground, and passed through a 200 mesh sieve to obtain acid-modified waste graphite powder; (3) The acid-modified waste graphite powder was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain an acid-modified waste graphite negative electrode material.

[0038] Comparative Example 2 (1) Soak the waste batteries in sodium chloride solution for 48 hours, discharge, dry, disassemble, grind, and pass through a 200-mesh sieve to obtain waste graphite powder; (2) The waste graphite powder was heated to 500°C at a heating rate of 5°C / min under a nitrogen atmosphere, kept at this temperature for 2 h, and naturally cooled to room temperature to obtain a modified waste graphite negative electrode material.

[0039] Performance Testing The graphite negative electrode materials prepared in the above examples and comparative examples were used as negative electrode materials for lithium batteries, and electrochemical performance tests were performed. The specific steps are as follows: Graphite negative electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) were weighed and mixed in N-methylpyrrolidone in a mass ratio of 8:1:1 to obtain a mixed slurry. The mixed slurry was then evenly coated on aluminum foil to obtain an electrode sheet and dried. A button half-cell was assembled in a glove box, using the above-mentioned electrode sheet as the working electrode, the metal lithium sheet as the counter electrode, LiPF6 as the lithium salt, EC, DMC, and DEC with a volume ratio of 1:1:1 as organic solvents, the lithium salt was dissolved in the organic solvent to prepare an electrolyte with a lithium salt concentration of 1M, and the diaphragm was a polypropylene (PP) diaphragm.

[0040] The electrochemical performance of the button cell prepared above was tested at a current density of 500 mA / g, and the discharge specific capacity of the first cycle and after 120 cycles is shown in Table 1.

[0041] Table 1 Performance test values ​​of button batteries prepared in Examples 1-6 and Comparative Examples 1-2

[0042] See also Figures 1 and 2 ,pass Figures 1 and 2 It can be seen that nano-calcium silicate hydrate is effectively combined with the surface of waste graphite to form a calcium silicate hydrate coating layer.

[0043] Please refer to Table 1. It can be seen from Table 1 that, compared with Comparative Example 2, the nano-hydrated calcium silicate modified waste graphite negative electrode materials prepared in Examples 1 to 6 of the present invention all have higher discharge specific capacity and cycle performance, and the repair effect on waste graphite is equivalent to that of traditional strong acid leaching (Comparative Example 1), indicating that the present invention can avoid acid washing and alkali washing without excessively affecting the repair effect, thereby reducing production costs.

[0044] Compared with Example 1, the discharge performance and cycle performance of the nano-calcium silicate hydrate modified waste graphite negative electrode materials obtained in Examples 3 to 4 are poor. The reason is that the theoretical content of calcium silicate hydrate is too low, resulting in an insignificant repair effect; the theoretical content of calcium silicate hydrate is too high, resulting in a low proportion of graphite in the negative electrode material and a decrease in conductivity, both of which are not conducive to improving the discharge performance and cycle performance.

[0045] Compared with Example 1, the discharge performance and cycle performance of the nano-calcium silicate hydrate modified waste graphite negative electrode materials obtained in Examples 5 to 6 are poor. The reason is that the soluble calcium salt accounts for too much, resulting in too much free calcium remaining in the synthesized calcium silicate hydrate, which affects the overall morphology and conductivity after drying; the soluble silicate accounts for too much, which affects the structure of the calcium silicate hydrate, resulting in poor repair effect, and is not conducive to improving the discharge performance and cycle performance.

[0046] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a waste graphite negative electrode material modified by nano-calcium silicate hydrate, characterized in that: The following steps are involved: Waste graphite powder, soluble calcium salt, soluble silicate and water are mixed and reacted, and then dried to obtain nano-hydrated calcium silicate modified waste graphite powder; The nanometer calcium silicate hydrate modified waste graphite powder is calcined to obtain the nanometer calcium silicate hydrate modified waste graphite negative electrode material.

2. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The waste graphite powder is obtained by discharging, disassembling, grinding and sieving waste batteries; The particle size of the waste graphite powder is below 200 meshes.

3. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The soluble calcium salt is at least one of calcium chloride, calcium nitrate, calcium formate, calcium acetate, calcium bicarbonate and calcium gluconate; The soluble silicate is at least one of sodium silicate, sodium fluorosilicate, potassium silicate and lithium silicate; The molar ratio of calcium in the soluble calcium salt to silicon in the soluble silicate is (0.5-3.0):

1.

4. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The mass ratio of the waste graphite powder to the theoretical content of calcium silicate hydrate is 1: (0.05-0.4); The mass ratio of the waste graphite powder to water is 1:(0.5~3).

5. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The particle size of the nano-calcium silicate hydrate modified waste graphite powder is below 200 meshes.

6. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The steps of mixing waste graphite powder, soluble calcium salt, soluble silicate and water for reaction and then drying to obtain nanometer calcium silicate hydrate modified waste graphite powder include: preparing a soluble calcium salt solution and a soluble silicate solution; Waste graphite powder, soluble calcium salt solution and soluble silicate solution are mixed and reacted, and then dried, ground and sieved to obtain nano-hydrated calcium silicate modified waste graphite powder; wherein, The mass fraction of the soluble calcium salt solution is 10wt%~40wt%; The mass fraction of the soluble silicate solution is 10wt%~30wt%; The waste graphite powder, the soluble calcium salt solution and the soluble silicate solution are mixed and reacted by adding the soluble calcium salt solution and the soluble silicate solution into the waste graphite powder at the same time and performing a mixing reaction.

7. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The temperature of the mixed reaction is 20-80° C., and the time of the mixed reaction is 4-12 hours.

8. The method for preparing the nano-calcium silicate hydrate modified waste graphite negative electrode material according to claim 1, characterized in that: The calcination temperature is 300-800° C., the calcination time is 1-5 hours, the heating rate is 2-5° C. / min, and the calcination is carried out under a protective atmosphere.

9. A nano-calcium silicate hydrate modified waste graphite negative electrode material, characterized in that: The nano-calcium silicate hydrate modified waste graphite negative electrode material is obtained by the preparation method of the nano-calcium silicate hydrate modified waste graphite negative electrode material according to any one of claims 1 to 8.

10. An application of the nano-calcium silicate hydrate modified waste graphite negative electrode material as claimed in claim 9, characterized in that: The nano-calcium silicate hydrate modified waste graphite negative electrode material is applied to lithium batteries.

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