A low-temperature lithium-ion battery negative electrode material and a method for preparing a low-temperature lithium-ion battery

Abstract

The present invention discloses a method for preparing a negative electrode material for a low-temperature lithium-ion battery, wherein the negative electrode material includes a porous carbon material and a carbon nanomaterial coated thereon, and the preparation method includes: 1. preparing a precursor solution; 2. adding the carbon material and a precipitant to the precursor solution for post-processing; 3. high-temperature activation; 4. methane cracking reaction; 5. hydrochloric acid etching; The method for preparing a battery using the negative electrode material of the present invention includes: 1. preparing a positive electrode sheet by using a lithium cobalt oxide material, PVDF, and a conductive agent; 2. preparing a negative electrode sheet by using a negative electrode material, SBR, and CMC; 3. isolating the positive electrode sheet and the negative electrode sheet and adding an electrolyte. The negative electrode material of the present invention is prepared by ion impregnation, methane in-situ cracking, and acid etching, and has a multi-pore structure, which improves the discharge platform voltage and discharge capacity of the negative electrode material in a low-temperature environment, and is suitable for low-temperature lithium-ion batteries; The battery preparation method of the present invention is simple and has high production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a low-temperature lithium ion battery negative electrode material and a preparation method of the low-temperature lithium ion battery. Background Art

[0002] Lithium-ion batteries, as new energy products, have found widespread application in a variety of fields, including drones, digital products, wearable security devices, and power tools. However, traditional lithium-ion batteries cannot be charged in ambient temperatures below 0°C. This is because when charging conventional lithium-ion batteries at temperatures below 0°C, lithium ions readily precipitate on the negative electrode surface, forming lithium dendrites. Repeated charging at low temperatures for extended periods can severely damage the battery's material structure, causing a sharp decline in performance and potentially posing safety risks. This is primarily due to the slow diffusion rate of lithium ions at low temperatures, resulting in a higher charge transfer impedance between the electrode and electrolyte during the lithium insertion process. Since the performance of low-temperature lithium-ion batteries is primarily influenced by the lithium ion transfer rate within the negative electrode material, improving the lithium ion diffusion rate within the graphite negative electrode is key to improving low-temperature performance. To address this challenge, the company plans to develop a lithium-ion battery capable of charging at temperatures of -20°C and above through extensive experimental research and formulation of modified negative electrode raw materials. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned prior art and provide a low-temperature lithium-ion battery negative electrode material. This negative electrode material is prepared by ion impregnation, in-situ methane cracking, and acid etching. It has a multi-pore structure and utilizes the hollow structure of nanotubes to effectively store lithium ions. This improves the negative electrode material's conductivity and effectively increases the diffusion rate of lithium ions in the negative electrode material, thereby increasing the negative electrode material's discharge platform voltage and discharge capacity in low-temperature environments. This solves the problem of the negative electrode material's low lithium ion transmission rate at low temperatures, which affects the performance of lithium-ion batteries.

[0004] To solve the above technical problems, the present invention adopts the following technical solution: a low-temperature lithium-ion battery negative electrode material, characterized in that it includes a porous carbon material and a carbon nanomaterial coated on the porous carbon material, and the carbon nanomaterial is distributed in the pores and surface of the porous carbon material; the negative electrode material is prepared by a method comprising the following steps:

[0005] Step 1: preparing a precursor solution of Fe, Ni or Cu metal ions;

[0006] Step 2: adding the carbon material and the precipitant to the precursor solution prepared in step 1 for post-treatment to obtain a dried product;

[0007] Step 3: Grind the dried product obtained in step 2 and place it in a muffle furnace for high-temperature activation to obtain an activated product;

[0008] Step 4: placing the activated product obtained in step 3 in a tubular reactor, introducing a methane mixture and heating the reactor to perform a methane cracking reaction;

[0009] Step 5: The activated product after the methane cracking reaction in step 4 is etched with hydrochloric acid, washed by centrifugation with deionized water, and dried to obtain a negative electrode material.

[0010] The above-mentioned low-temperature lithium-ion battery negative electrode material is characterized in that the precursor of the Fe metal ion in step 1 is at least one of FeCl3, Fe(NO3)3 and FeSO4, the precursor of the Cu metal ion is Cu(NO3)2, and the precursor of the Ni metal ion is Ni(NO3)2.6H2O, and the concentration of the Fe, Ni or Cu metal ions is 1.2mol / L to 1.6mol / L. By controlling the concentration of the metal ions, it is avoided that an excessive amount of metal ions accumulates on the surface of the carbon material after high-temperature activation, which is not conducive to the dispersion of the metal ions on the surface and inside the carbon material, affecting the uniformity of the pores generated in the carbon material by the subsequent methane cracking reaction.

[0011] The above-mentioned low-temperature lithium-ion battery negative electrode material is characterized in that the carbon material in step 2 is graphite powder, the precipitant is ammonium carbonate, and the amount of ammonium carbonate is 1.2 to 2.0 times the amount of Fe, Ni, or Cu metal ions in the precursor solution, and the amount of carbon material is 0.75 to 1 times the amount of precursor salt in the precursor solution. By controlling the addition ratio of the precipitant, the active metal ions are ensured to be completely precipitated.

[0012] The aforementioned low-temperature lithium-ion battery negative electrode material is characterized in that the post-treatment in step 2 comprises: stirring at 60°C for 8 hours, filtering, and drying the filter residue in an oven at 120°C. Stirring during post-treatment promotes the deposition of active metal ions on the surface of the carbon material.

[0013] The above-mentioned low-temperature lithium-ion battery negative electrode material is characterized in that the high-temperature activation process in step three is: heating to 700°C at a rate of 5°C / min and calcining for 8 hours, and grinding to obtain an activated product. Usually, under a 95% Ar-5% O2 protective atmosphere, the temperature is first raised to 500°C at a rate of 10°C / min and maintained for 5 minutes, and then heated to 700°C at a rate of 5°C / min. Different temperatures during the high-temperature activation process will form different crystal phases. The present invention strictly controls the high-temperature activation process, especially the temperature, so that the metal ions adsorbed and deposited on the surface of the carbon material react to form metal oxides, thereby causing the metal oxides to undergo a partial redox reaction with methane to generate active metal elements, and further undergo a cracking reaction with methane to generate carbon nanomaterials, thereby avoiding the formation of impurities.

[0014] The aforementioned low-temperature lithium-ion battery negative electrode material is characterized in that the methane concentration in the methane mixture in step 4 is 5% by volume, the flow rate is 60 mL / min, and the temperature of the methane cracking reaction is 800°C. Typically, the methane cracking reaction is carried out for 30 minutes after the methane mixture is introduced. A mass spectrometer is used to monitor the generated gas from the methane cracking reaction to determine the composition and content of the generated gas, thereby confirming the loading amount of the carbon nanomaterial.

[0015] The above-mentioned low-temperature lithium-ion battery negative electrode material is characterized in that in step five, hydrochloric acid with a mass concentration of 15% is used to etch and remove the metal oxide, and the drying is carried out in a drying oven at 120° C. for 12 hours.

[0016] At the same time, the present invention also discloses a method for preparing a low-temperature lithium-ion battery using the above-mentioned negative electrode material, characterized in that the method comprises the following steps:

[0017] Step 1: prepare the positive electrode sheet by dry mixing the lithium cobalt oxide material, PVDF, and conductive agent in a mass ratio of 95.8-96.6:1.6-2.0:1.8-2.2;

[0018] Step 2: Prepare the negative electrode sheet by dry batching the negative electrode material, SBR, and CMC according to a mass ratio of 97.3-97.8:1.2-2.0:1.3-1.8;

[0019] Step 3: Isolate the positive electrode sheet produced in step 1 and the negative electrode sheet produced in step 2 with an isolation film, and add electrolyte to prepare a lithium-ion battery.

[0020] The above method is characterized in that no conductive agent needs to be added during the production of the negative electrode sheet in step 2.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The present invention first mixes the carbon material with metal ions, performs post-treatment and high-temperature activation to obtain an activated product of a mixture of carbon material and metal oxide. In the subsequent methane cracking reaction, the metal oxide undergoes a partial redox reaction with methane, and the metal oxide generates a metal element, which further undergoes a cracking reaction with methane, and is coated and deposited on the surface and inside the pores of the carbon material to generate carbon nanomaterials including carbon nanotubes and carbon nanofibers. At the same time, when the hydrogen generated during the reaction is released from the inside of the carbon material, a large number of micropores are generated inside the carbon material, thereby improving the pore size distribution of the carbon material and increasing the porosity of the carbon material, thereby obtaining a negative electrode material with a multi-pore structure. The hollow structure of the carbon nanotubes cooperates to effectively store lithium ions, thereby improving the conductivity of the negative electrode material, effectively increasing the diffusion rate of lithium ions in the negative electrode material, and improving the discharge platform voltage and discharge capacity of the negative electrode material under low-temperature conditions, thereby being suitable for low-temperature lithium-ion batteries.

[0023] 2. The present invention modifies the negative electrode material through an in-situ reaction of methane cracking. The in-situ generated carbon nanomaterial is evenly distributed and tightly bound to the surface and interior of the carbon material, which effectively improves the dispersion of the carbon nanomaterial, is beneficial to improving the migration ability of electrons in the negative electrode material under high-rate discharge, reducing the polarization phenomenon during the charge and discharge process, and improving the charge and discharge capacity of the lithium-ion battery. Therefore, the negative electrode material prepared by the method of the present invention has excellent electrochemical reaction performance, and is better than the in-situ generation of carbon nanomaterials on the surface and interior of the negative electrode material by methane cracking. Therefore, there is no need to further add conductive agent materials in the subsequent preparation of negative electrode sheets, which simplifies the ingredient preparation process and reduces the difficulty of ingredient preparation.

[0024] 3. The present invention adopts hydrochloric acid etching to remove excess metal oxides in the activated product after the methane cracking reaction on the one hand, and to perform acid etching on the metal element generated by the partial redox reaction of the metal oxide and methane on the other hand, thereby forming staggered pores in the negative electrode material, effectively increasing the storage space of the electrolyte, thereby increasing the rate of lithium ion insertion and extraction between the negative electrode plate and the electrolyte interface, and reducing the polarization phenomenon during the low-temperature discharge process of the lithium-ion battery, thereby achieving high rate and low-temperature discharge performance of the lithium-ion battery.

[0025] 4. The present invention improves the porosity of the carbon material and realizes the filling of carbon nanomaterials by adjusting the process parameters of the methane cracking reaction, thereby improving the porosity and conductivity of the negative electrode material, greatly improving the low-temperature rate performance of the lithium-ion battery, and enabling the lithium-ion battery to achieve excellent charge and discharge performance in a temperature environment of -20°C and above, and can be stored and used under high temperature conditions.

[0026] 5. The preparation method of the negative electrode material of the present invention is simple and has high production efficiency. In addition, the methane cracking reaction in the preparation process effectively consumes greenhouse gas methane and produces clean energy hydrogen, which helps to reduce the greenhouse effect.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the in-situ cracking of methane onto the active metal surface in Example 1 of the present invention.

[0029] Figure 2 This is a test chart of the electrochemical performance of the lithium-ion batteries prepared in Examples 1 to 3 of the present invention and Comparative Example 1 at a temperature above -20°C.

[0030] Figure 3 This is a test diagram of the electrochemical performance of the lithium-ion batteries prepared in Example 2 of the present invention and Comparative Example 1 after 500T of cycling at -20°C. DETAILED DESCRIPTION

[0031] Figure 1 Schematic diagram of in-situ cracking of methane onto the active metal surface in Example 1 of the present invention, Figure 1 It can be seen that methane and metal elements on the surface and inside of the negative electrode material are decomposed to produce carbon nanotubes. The hollow structure of the nanotubes can serve as a warehouse for lithium ion transmission, which is beneficial to the transmission of lithium ions in the electrode, so that the negative electrode material has a higher lithium ion transmission rate, improves the conductivity of the negative electrode material, and reduces the low-temperature polarization phenomenon of the lithium-ion battery.

[0032] The low-temperature lithium-ion battery negative electrode material of the present invention is described in detail through Examples 1 to 3.

[0033] Example 1

[0034] The negative electrode material of the low-temperature lithium-ion battery of this embodiment includes a porous carbon material and a carbon nanomaterial coated on the porous carbon material, and the carbon nanomaterial is distributed in the pores and surface of the porous carbon material; the negative electrode material is prepared by a method comprising the following steps:

[0035] Step 1: Dissolve Ni(NO3)2.6H2O in deionized water at 60°C to obtain 60 mL of a precursor solution with a concentration of 1.2 mol / L;

[0036] Step 2: 16 g of graphite powder and 8.29 g of ammonium carbonate as a precipitant were added to the precursor solution prepared in step 1, the pH was adjusted to 8 with aqueous ammonia, and the mixture was stirred in a 60°C water bath for 8 h. After filtering, the filter residue was dried in an oven at 120°C for 12 h to obtain a dried product;

[0037] Step 3: Grind the dried product obtained in step 2 and place it in a muffle furnace. Under an argon protective atmosphere, heat it to 500°C at a rate of 10°C / min and hold it for 5 minutes, then heat it to 700°C at a rate of 5°C / min and calcine it for 8 hours to obtain an activated product after grinding.

[0038] Step 4: 16 g of the activated product obtained in step 3 was placed in a tubular reactor, and a methane mixture with a methane volume concentration of 5% was introduced at a flow rate of 60 mL / min and the temperature was raised to 800° C. to perform a methane cracking reaction. At the same time, a mass spectrometer was used to monitor the generated gas of the methane cracking reaction to confirm the component content of the generated gas and further confirm the loading amount of the carbon nanomaterial;

[0039] Step 5: The activated product after the methane cracking reaction in step 4 is etched with 15% hydrochloric acid to remove the metal oxide, and then centrifuged and washed with deionized water and dried in a drying oven at 120° C. for 12 hours to obtain a negative electrode material.

[0040] The precursor solution in this embodiment can also be replaced by a precursor solution containing Fe or Cu metal ions, and the precursor of the Fe metal ions is at least one of FeCl3, Fe(NO3)3 and FeSO4, and the precursor of the Cu metal ions is Cu(NO3)2.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that the concentration of the precursor solution in step 1 is 1.4 mol / L, and the mass of the precipitant ammonium carbonate is 9.67 g.

[0043] The precursor solution in this embodiment can also be replaced by a precursor solution containing Fe or Cu metal ions, and the precursor of the Fe metal ions is at least one of FeCl3, Fe(NO3)3 and FeSO4, and the precursor of the Cu metal ions is Cu(NO3)2.

[0044] Example 3

[0045] The difference between this embodiment and embodiment 1 is that in step 1, the concentration of the precursor solution is 1.6 mol / L, and the mass of the precipitant ammonium carbonate is 11.05 g.

[0046] The precursor solution in this embodiment can also be replaced by a precursor solution containing Fe or Cu metal ions, and the precursor of the Fe metal ions is at least one of FeCl3, Fe(NO3)3 and FeSO4, and the precursor of the Cu metal ions is Cu(NO3)2.

[0047] The preparation method of the low-temperature lithium-ion battery of the present invention is described in detail through Example 4.

[0048] Example 4

[0049] This embodiment includes the following steps:

[0050] Step 1: lithium cobalt oxide material, PVDF, and conductive agent are prepared by dry mixing in a mass ratio of 95.8:2.0:2.2 to form a positive electrode sheet, wherein the conductive agent is carbon nanoparticle slurry with a solid content of 4.3%;

[0051] Step 2: The negative electrode material of Example 2, SBR, and CMC are mixed in a mass ratio of 97:1.2:1.8 using a dry method to prepare a negative electrode sheet;

[0052] Step 3: Isolate the positive electrode sheet produced in step 1 and the negative electrode sheet produced in step 2 with a highly permeable and high-porosity coated diaphragm made of PE material, and add an electrolyte containing LiPF6, EC, EMC, DMC and anti-low-temperature additives to prepare a lithium-ion battery.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 4 is that in step 2, conventional negative electrode materials are used to prepare the negative electrode sheet. The preparation method of the conventional negative electrode material includes the following steps:

[0055] Step 1: Wash the wood chips with deionized water and dry them in a drying oven at 120°C for 2 hours. Then, soak them in a 2M sulfuric acid solution and heat them in a constant temperature water bath at 70°C for 2 hours to remove metal impurities. After filtering, wash them with deionized water until they are neutral, and dry them at 120°C for 2 hours to obtain a pre-treated product for later use.

[0056] Step 2: Mix the pre-treated product in step 1 with 2M FeCl3 solution and stir for 12 hours. After vacuum filtration, dry it in a drying oven at 120°C for 12 hours. Then place it in a tubular reactor filled with nitrogen and keep it at 800°C for 3 hours for carbonization. Then soak it in 1M sulfuric acid for 12 hours, wash it with deionized water until it is neutral, and obtain unmodified conventional negative electrode material after drying.

[0057] The lithium ion batteries prepared in Examples 1 to 3 of the present invention and Comparative Example 1 were subjected to charge and discharge tests using a Xinwei test device: the lithium ion batteries were first charged and discharged at room temperature using a 0.5 CI A Discharge to 3.0V, then place at -20℃ for 4h, charge and discharge the battery at 1C, and record the charge and discharge capacity. The results are as follows Figure 2 and Figure 3 shown.

[0058] Figure 2 The electrochemical performance test diagram of the lithium ion batteries prepared in Examples 1 to 3 of the present invention and Comparative Example 1 at a temperature above -20°C is shown. Figure 2It can be seen that compared with the lithium ion battery prepared using conventional negative electrode materials in Comparative Example 1, the lithium ion batteries prepared in Examples 1 to 3 of the present invention have excellent charge and discharge performance, among which Example 2 is the best.

[0059] Figure 3 The electrochemical performance test diagram of the lithium ion batteries prepared in Example 2 of the present invention and Comparative Example 1 after 500T of cycling at -20°C is shown in FIG. Figure 3 It can be seen that the gram capacity of the lithium-ion battery assembled with the negative electrode material of Example 2 is 115.79 mAh / g, which is significantly greater than the gram capacity of the lithium-ion battery assembled with the conventional negative electrode material in Comparative Example 1, which is 96.76 mAh / g. This shows that the lithium-ion battery assembled with the negative electrode material prepared by the present invention has excellent cycle retention rate under low temperature conditions of -20°C.

[0060] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A low-temperature lithium-ion battery negative electrode material, characterized in that: The negative electrode material comprises a porous carbon material and a carbon nanomaterial coated on the porous carbon material, wherein the carbon nanomaterial is distributed in the pores and surface of the porous carbon material; the negative electrode material is prepared by a method comprising the following steps: Step 1: preparing a precursor solution of Fe, Ni or Cu metal ions; Step 2: adding the carbon material and the precipitant to the precursor solution prepared in step 1 for post-treatment to obtain a dried product; The carbon material is graphite powder, the precipitant is ammonium carbonate, and the amount of ammonium carbonate is 1.2 to 2.0 times the amount of Fe, Ni or Cu metal ions in the precursor solution, and the amount of the carbon material is 0.75 to 1 times the amount of the precursor salt in the precursor solution; Step 3: Grind the dried product obtained in step 2 and place it in a muffle furnace for high-temperature activation to obtain an activated product; the high-temperature activation process is: heating to 700°C at a rate of 5°C / min and calcining for 8 hours, and then grinding to obtain an activated product; Step 4: placing the activated product obtained in step 3 in a tubular reactor, introducing a methane mixture and heating it to perform a methane cracking reaction; the methane volume concentration in the methane mixture is 5%, the introduction flow rate is 60 mL / min; the temperature of the methane cracking reaction is 800°C; Step 5: The activated product after the methane cracking reaction in step 4 is etched with hydrochloric acid, washed by centrifugation with deionized water, and dried to obtain a negative electrode material.

2. A low-temperature lithium-ion battery negative electrode material according to claim 1, characterized in that: In step 1, the precursor of the Fe metal ion is at least one of FeCl3, Fe(NO3)3 and FeSO4, the precursor of the Cu metal ion is Cu(NO3)2, and the precursor of the Ni metal ion is Ni(NO3)2·6H2O, and the concentration of the Fe, Ni or Cu metal ions is 1.2 mol / L~1.6 mol / L.

3. A low-temperature lithium-ion battery negative electrode material according to claim 1, characterized in that: The post-treatment in step 2 is as follows: stirring at 60° C. for 8 h, filtering, and drying the filter residue in an oven at 120° C.

4. A low-temperature lithium-ion battery negative electrode material according to claim 1, characterized in that: In step five, 15% mass concentration hydrochloric acid is used to etch and remove the metal oxide, and the drying is carried out in a drying oven at 120° C. for 12 hours.

5. A method for preparing a low-temperature lithium-ion battery using the negative electrode material according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1: Prepare the positive electrode sheet by dry mixing the lithium cobalt oxide material, PVDF, and conductive agent in a mass ratio of 95.8-96.6:1.6-2.0:1.8-2.2; Step 2: Prepare the negative electrode sheet by dry batching the negative electrode material, SBR, and CMC according to a mass ratio of 97.3-97.8:1.2-2.0:1.3-1.8; Step 3: Isolate the positive electrode sheet produced in step 1 and the negative electrode sheet produced in step 2 with an isolation film, and add electrolyte to prepare a lithium-ion battery.

6. The method according to claim 5, characterized in that No conductive agent is required during the production of the negative electrode sheet in step 2.

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