A fast-charging graphite composite material and a preparation method thereof

Abstract

The application discloses a kind of fast-charging graphite composite material and preparation method thereof.A kind of fast-charging graphite composite material, by core and outer layer, the outer layer is covered core;Wherein, the core is graphite;The outer layer is formed by Li5FeO4, metal oxide and amorphous carbon composite.The application further discloses the preparation method of the graphite composite material.The fast-charging graphite composite material and preparation method thereof described in the application, surface coating is carried out using metal oxide, with the advantages of high energy density, high first efficiency, and by lithium supplement to improve the energy density and power performance of material.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery materials, specifically relating to a fast-charging graphite composite material and its preparation method. Background Technology

[0002] As the requirements for energy density and fast charging performance of lithium-ion batteries increase, lithium-ion battery anode materials must not only have high energy density, but also improve their fast charging performance.

[0003] Currently, commercially available anode materials are mainly composed of artificial graphite, with a theoretical specific capacity of 372 mAh / g. However, they suffer from low energy density, layered structure with long intercalation / deintercalation paths, limiting their fast-charging performance to ≤4C. EOL (End-of-Life) expansion is around 35%, and the initial efficiency is only 92-94%. These factors contribute to the slightly poor charging capability and initial efficiency of the anode material, affecting the improvement of the overall battery's energy density and fast-charging performance. Surface coating is one of the main measures to improve the material's kinetic properties. Currently, conventional coatings use soft carbon / hard carbon, which suffers from insufficient kinetics and low initial efficiency after coating.

[0004] In view of this, the present invention proposes a new fast-charging graphite composite material and its preparation method, which can improve the fast charging, initial charging efficiency and energy density of graphite materials. Summary of the Invention

[0005] The purpose of this invention is to provide a new fast-charging graphite composite material, which uses metal oxide for surface coating, has the advantages of high energy density and high initial efficiency, and improves the initial efficiency, energy density and power performance of the material by lithium supplementation.

[0006] To achieve the above objectives, the technical solution adopted is as follows:

[0007] A fast-charging graphite composite material, consisting of a core and an outer layer, wherein the outer layer covers the core;

[0008] The core is graphite;

[0009] The outer layer is composed of Li5FeO4, metal oxides and amorphous carbon.

[0010] Furthermore, in the outer layer, the mass fraction of Li5FeO4 is 1-10%, the mass fraction of metal oxide is 0.5-5%, and the remainder is amorphous carbon.

[0011] Furthermore, the metal oxide is one of titanium oxide, zirconium oxide, aluminum oxide, niobium oxide, tungsten oxide, and cobalt oxide.

[0012] Another object of the present invention is to provide a method for preparing the above-mentioned graphite composite material, wherein the method deposits metal oxides and Li5FeO4 lithium supplements on the graphite surface by atomic vapor deposition, thereby improving the initial efficiency and fast charging performance of the material.

[0013] To achieve the above objectives, the technical solution adopted is as follows:

[0014] The above-mentioned method for preparing graphite composite materials includes the following steps:

[0015] (1) Using graphite as a substrate, metal oxide and Li5FeO4 as reaction sources, atomic vapor deposition is used to repeatedly deposit metal oxide and Li5FeO4 on graphite 1-100 times to obtain graphite precursor material.

[0016] (2) After uniformly dispersing the graphite precursor material in the resin solution, spray drying is performed, followed by heat treatment at 800-1200℃ for 1-6 hours, and finally high-temperature graphitization is performed to obtain the graphite composite material.

[0017] Furthermore, in step (1), each atomic layer deposition is performed in the order of two metal oxides and two Li5FeO4.

[0018] Furthermore, in step (1), each atomic layer deposition is performed in the order of one metal oxide and one Li5FeO4, and this is considered as a cycle.

[0019] Furthermore, in the atomic vapor deposition of step (1), the reaction temperature is 100-200℃, the vacuum degree is 1-10 tor, nitrogen gas is pulsed and cleaned for 4s, and then water vapor is pulsed for 0.1s.

[0020] Furthermore, in step (2), the mass ratio of graphite precursor material to resin is 100:5-20.

[0021] Furthermore, the mass-to-volume ratio of resin to solvent in the resin solution is 1-10g:100ml.

[0022] Furthermore, the resin is one of phenolic resin, furfural resin, and epoxy resin;

[0023] The solvent is one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The technical solution of the present invention uses atomic vapor deposition to sequentially deposit metal oxide and Li5FeO4. Relying on the advantages of high specific capacity and high initial efficiency of metal oxide, and the strong lithium-ion diffusion ability of Li5FeO4, which replenishes lithium ions during charging and discharging, the irreversible capacity loss of the negative electrode material can be reduced and the initial efficiency can be improved.

[0026] 2. The technical solution of the present invention adopts atomic vapor deposition, which has the advantages of high deposition density, strong consistency, and achieving the best effect with the minimum deposition amount, thereby improving the power performance and cycle performance of the material.

[0027] 3. The technical solution of the present invention uses sequential deposition, which allows the metal oxide and lithium replenishment agent to fully react during the charging and discharging process to generate inorganic lithium salt compounds and reduce the irreversible loss of the material. At the same time, sequential deposition results in high material density and restrains the expansion of the material during the charging and discharging process. Attached Figure Description

[0028] Figure 1 The image shows a SEM image of the graphite composite material prepared in Example 1. Detailed Implementation

[0029] To further illustrate the fast-charging graphite composite material and its preparation method according to the present invention, and to achieve the intended purpose of the invention, the following detailed description, in conjunction with preferred embodiments, details the specific implementation, structure, features, and effects of the fast-charging graphite composite material and its preparation method proposed according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0030] The following will provide a more detailed description of the fast-charging graphite composite material and its preparation method according to the present invention, with reference to specific embodiments:

[0031] This invention discloses a fast-charging graphite composite material and its preparation method. The composite material consists of a graphite core and a Li5FeO4 / metal oxide / amorphous carbon composite coating on the core surface. The coating layer contains 1-10% Li5FeO4, 0.5-5% metal oxide, and the remainder is amorphous carbon. The coating layer utilizes the high lithium-ion conductivity of the Li5FeO4 solid electrolyte to enhance the lithium-ion transport rate; the high initial efficiency and low impedance of the metal oxide enhance the specific capacity of the full battery; the electronic conductivity and excellent processing performance of the amorphous carbon enhance the electron transport rate; and the network structure formed by the coupling agent improves the structural stability of the material. The prepared composite material exhibits excellent rate performance and high initial efficiency.

[0032] The technical solution of this invention is as follows:

[0033] A fast-charging graphite composite material, consisting of a core and an outer layer, wherein the outer layer covers the core;

[0034] The core is graphite;

[0035] The outer layer is composed of Li5FeO4, metal oxides and amorphous carbon.

[0036] Preferably, in the outer layer, the mass fraction of Li5FeO4 is 1-10%, the mass fraction of metal oxide is 0.5-5%, and the remainder is amorphous carbon.

[0037] Preferably, the metal oxide is one of titanium oxide, zirconium oxide, aluminum oxide, niobium oxide, tungsten oxide, and cobalt oxide.

[0038] The above-mentioned method for preparing graphite composite materials includes the following steps:

[0039] (1) Using graphite as a substrate, metal oxide and Li5FeO4 as reaction sources, atomic vapor deposition is used to repeatedly deposit metal oxide and Li5FeO4 on graphite 1-100 times to obtain graphite precursor material.

[0040] (2) After uniformly dispersing the graphite precursor material in the resin solution, spray drying is performed, followed by heat treatment at 800-1200℃ for 1-6 hours, and finally high-temperature graphitization is performed to obtain the graphite composite material.

[0041] Preferably, in step (1), each atomic layer deposition is performed in the order of one metal oxide and one Li5FeO4.

[0042] More preferably, in step (1), the deposition time of each metal oxide is 1-3 seconds, and the deposition time of each Li5FeO4 is 0.5-1 seconds, and this is considered as a cycle.

[0043] Preferably, in the atomic vapor deposition of step (1), the reaction temperature is 100-200℃, the vacuum degree is 1-10 tor, nitrogen gas is pulsed and cleaned for 4s, and then water vapor is pulsed for 0.1s.

[0044] Preferably, in step (2), the mass ratio of graphite precursor material to resin is 100:5-20.

[0045] More preferably, the mass-to-volume ratio of resin to solvent in the resin solution is 1-10g:100ml.

[0046] More preferably, the resin is one of phenolic resin, furfural resin, and epoxy resin;

[0047] The solvent is one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride.

[0048] Example 1.

[0049] The specific operating steps are as follows:

[0050] (1) Atomic vapor deposition was used with artificial graphite as the substrate. At 150°C and a vacuum of 5 tor, titanium oxide and Li5FeO4 were used as reaction sources for deposition. Then, nitrogen pulse cleaning was carried out for 4 s, and finally water vapor pulse cleaning was carried out for 0.1 s. The deposition was repeated 50 times to obtain the artificial graphite precursor material.

[0051] Each titanium oxide cycle deposition time was 2 seconds, and each Li5FeO4 deposition time was 1 second. Each atomic layer deposition cycle consisted of one titanium oxide cycle and one Li5FeO4 cycle performed sequentially.

[0052] (2) Add 10g of phenolic resin to 200ml of organic solvent of carbon tetrachloride, and disperse it evenly by ultrasonication to obtain phenolic resin solution.

[0053] Add 100g of artificial graphite precursor material, mix evenly, spray dry, and transfer the obtained product to a tube furnace. Under an inert argon atmosphere, heat to 900℃ and hold for 3 hours, then graphitize at 2800℃ for 24 hours to obtain graphite composite material.

[0054] ICP and its carbon-sulfur analyzer showed that the mass fraction of Li5FeO4 was 5%, the mass fraction of metal oxides was 2.4%, and the remainder was amorphous carbon.

[0055] Example 2.

[0056] The specific operating steps are as follows:

[0057] (1) Atomic vapor deposition was used with artificial graphite as the substrate. Under the conditions of 100℃ and 1 tor vacuum, zirconium oxide and Li5FeO4 were used as reaction sources for deposition. Then, nitrogen pulse was introduced for 4s cleaning, and finally water vapor pulse was introduced for 0.1s. The deposition was repeated 10 times to obtain the artificial graphite precursor material.

[0058] Each zirconium oxide cycle deposition time was 1 second, and each Li5FeO4 deposition time was 0.5 seconds. Each atomic layer deposition cycle consisted of one zirconium oxide cycle and one Li5FeO4 cycle performed sequentially.

[0059] (2) Add 5g of epoxy resin to 500ml of cyclohexane solution, and disperse it evenly by ultrasonication to obtain epoxy resin solution.

[0060] Add 100g of artificial graphite precursor material, mix evenly, spray dry, and transfer the obtained product to a tube furnace. Under an inert argon atmosphere, heat to 800℃ and hold for 6 hours, then graphitize at 2800℃ for 24 hours to obtain graphite composite material.

[0061] ICP and its carbon-sulfur analyzer showed that the mass fraction of Li5FeO4 was 1%, the mass fraction of metal oxides was 0.5%, and the remainder was amorphous carbon.

[0062] Example 3.

[0063] The specific operating steps are as follows:

[0064] (1) Atomic vapor deposition was used with artificial graphite as the substrate. Under the conditions of 200℃ and 10 tor vacuum, niobium oxide and Li5FeO4 were used as reaction sources for deposition. Then, nitrogen pulse was introduced for 4s cleaning, and finally water vapor pulse was introduced for 0.1s. The deposition was repeated 100 times to obtain the artificial graphite precursor material.

[0065] Each oxide deposition took 3 seconds, and each Li5FeO4 deposition took 1 second. Each atomic layer deposition consisted of a sequential process of niobium oxide and Li5FeO4.

[0066] (2) Add 20g of furfural resin to 200ml of N-methylpyrrolidone, and after ultrasonic dispersion, obtain furfural resin solution.

[0067] Add 100g of artificial graphite precursor material, spray dry, transfer the obtained product to a tube furnace, heat to 1200℃ and hold for 1h under an argon inert atmosphere, then graphitize at 2800℃ for 24h to obtain graphite composite material.

[0068] ICP and its carbon-sulfur analyzer showed that the mass fraction of Li5FeO4 was 10%, the mass fraction of metal oxides was 5%, and the remainder was amorphous carbon.

[0069] Comparative Example 1:

[0070] Add 5g of epoxy resin to 500ml of cyclohexane solution, and disperse evenly by ultrasonication to obtain an epoxy resin solution.

[0071] Add 100g of artificial graphite, spray dry, and transfer the obtained product to a tube furnace. Under an inert argon atmosphere, heat to 800℃ and hold for 6 hours, then graphitize at 2800℃ for 24 hours to obtain the artificial graphite composite material.

[0072] Comparative Example 2:

[0073] Add 5g of epoxy resin to 500ml of cyclohexane solution, and disperse evenly by ultrasonication to obtain an epoxy resin solution.

[0074] Add 5g of titanium dioxide and 5g of Li5FeO4 and mix evenly. Then add 100g of artificial graphite, spray dry, and transfer the obtained product to a tube furnace. Under an inert argon atmosphere, heat to 800℃ and hold for 6 hours. Then graphitize at 2800℃ for 24 hours to obtain artificial graphite composite material.

[0075] 1. Physicochemical property testing

[0076] 1.1 SEM Testing

[0077] The artificial graphite composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown. By Figure 1 As can be seen from the results, the artificial graphite composite material prepared in Example 1 is spherical with a uniform size distribution and a particle size between 8 and 15 μm.

[0078] 1.2 Powder conductivity test:

[0079] The powder was pressed into a block structure, and then its electrical conductivity was tested using a four-probe tester. The test results are shown in Table 1.

[0080] 1.3 Powder compaction density test

[0081] The compacted density of the artificial graphite composite materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested. During the test, a certain mass of powder was weighed and placed into a mold, then pressed under a pressure of 2T (using a powder compaction density meter, 1g of powder was placed in a fixed container and pressed under 2T pressure, left to stand for 10 seconds, and then the volume under compression was calculated, and the compacted density was calculated). The test results are shown in Table 1.

[0082] Table 1

[0083] project Powder resistivity (Ω·m) <![CDATA[Apparent density of powder (g / cm 3 )]]> Example 1 <![CDATA[6×10 -7 ]]> 1.69 Example 2 <![CDATA[7×10 -7 ]]> 1.67 Example 3 <![CDATA[3×10 -7 ]]> 1.65 Comparative Example 1 <![CDATA[8×10 -6 ]]> 1.54 Comparative Example 2 <![CDATA[5×10 -6 ]]> 1.55

[0084] As shown in Table 1, the resistivity of the graphite composite materials prepared in Examples 1-3 is significantly lower than that of the comparative examples. The examples employed a graphite-encapsulated oxide and Li5FeO4 bilayer structure to reduce electronic impedance and thus powder resistivity. This demonstrates that metal oxides, carbon nanotubes, nitrogen-containing substances, and amorphous carbon need to be in appropriate proportions to achieve the effect of reducing resistivity; more of any single component is not necessarily better. Compared to the comparative examples, the powder compaction density of the examples is not significantly different, but the overall density is higher, indicating that the composite graphite material prepared in the examples has a higher powder compaction density and a higher mass of active material per unit volume, thus better improving battery capacity.

[0085] 2. Button cell battery test

[0086] The artificial graphite composite materials from Examples 1-3 and Comparative Examples 1-2 were assembled into button cells A1, A2, A3, B1, and B2, respectively. The assembly method was as follows: a binder, conductive agent, and solvent were added to the negative electrode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The binder used was LA132 binder, the conductive agent was SP, the negative electrode material was the artificial graphite composite material from Examples 1-3 and Comparative Examples 1-2, and the solvent was double-distilled water. The proportions of each component were: negative electrode material: SP: LA132: double-distilled water = 95g: 1g: 4g: 220mL; the electrolyte was LiPF6 / EC+DEC (LiPF6 concentration was 1.2mol / L, EC and DEC volume ratio was 1:1), the lithium metal sheet was used as the counter electrode, and the separator was a polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane. The button cell assembly was carried out in an argon-filled glove box. Electrochemical performance testing was conducted on a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The test results are shown in Table 2.

[0087] Meanwhile, the above negative electrode was taken and its liquid absorption capacity was tested. The results are shown in Table 2.

[0088] Table 2 compares the liquid absorption performance of the coin cells and their electrodes in the examples and comparative examples.

[0089] project Initial discharge capacity (mAh / g) First-time efficiency (%) Liquid absorption capacity (mL / min) Example 1 / A1 362.3 97.3 9.8 Example 2 / A2 360.4 96.9 9.3 Example 3 / A3 360.5 97.7 9.9 Comparative Example 1 / B1 352.4 91.2 3.4 Comparative Example 2 / B2 351.7 92.0 3.6

[0090] As shown in Table 2, the lithium-ion batteries using the graphite composite anode materials obtained in Examples 1-3 exhibit significantly higher initial discharge capacity, initial charge-discharge efficiency, and liquid absorption capacity compared to the comparative examples. The dense metal oxide and its Li5FeO4 deposition structure reduces impedance and minimizes irreversible capacity loss. Simultaneously, Li5FeO4 provides lithium ions for the initial charge-discharge cycle, improving the initial efficiency. Furthermore, compared to the soft carbon coating, the metal oxide has a higher specific capacity, thus enhancing the specific capacity of the materials in these examples.

[0091] 3. Pouch Battery Testing

[0092] Anode sheets were prepared using the artificial graphite composite materials from Examples 1-3 and Comparative Examples 1-2 as the anode materials. Ternary materials (LiNi) were also used. 1 / 3 Co 1 / 3 Mn 1 / 3Using O2 as the positive electrode, LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.3 mol / L) as the electrolyte, and Celegard 2400 as the separator, 2Ah pouch cells A10, A20, A30, B10, and B20 were prepared. The cycle performance and rate performance of the pouch cells were then tested.

[0093] Rate performance test conditions: charging rate: 1C / 2C / 3C / 5C, discharging rate: 1C; voltage range: 2.8-4.2V.

[0094] The cycle test conditions were 1C / 1C, 2.8-4.2V, temperature: 25±3℃, and 500 cycles.

[0095] The test results are shown in Table 3.

[0096] Table 3

[0097]

[0098] As shown in Table 3, the soft-pack batteries prepared from the graphite composite materials in Examples 1-3 of this invention exhibit better constant current ratios. The constant current ratios of Comparative Examples 1 and 2 are significantly lower because the oxides deposited using atomic vapor deposition have advantages such as structural stability and low impedance. Furthermore, Li5FeO4 provides sufficient lithium ions for the charge and discharge process, thereby improving rate performance, i.e., increasing the constant current ratio of the material. Simultaneously, the use of atomic vapor deposition to stabilize the structure of the material's coating layer and the sufficient lithium ions provided by Li5FeO4 are beneficial for cycle performance.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A fast-charging graphite composite material, characterized in that, The graphite composite material consists of a core and an outer layer, wherein the outer layer covers the core. The core is graphite; The outer layer is composed of Li5FeO4, metal oxides and amorphous carbon. In the outer layer, the mass fraction of Li5FeO4 is 1-10%, the mass fraction of metal oxide is 0.5-5%, and the remainder is amorphous carbon; The metal oxide is one of titanium oxide, zirconium oxide, aluminum oxide, niobium oxide, tungsten oxide, and cobalt oxide; The preparation method of the graphite composite material includes the following steps: (1) Using graphite as a substrate, metal oxide and Li5FeO4 as reaction sources, atomic vapor deposition is used to deposit metal oxide and Li5FeO4 on graphite 1-100 times to obtain graphite precursor material; each deposition is carried out in the order of metal oxide once and Li5FeO4 once. (2) After uniformly dispersing the graphite precursor material in the resin solution, spray drying is performed, followed by heat treatment at 800-1200℃ for 1-6 hours, and finally high-temperature graphitization is performed to obtain the graphite composite material.

2. The method for preparing the graphite composite material according to claim 1, characterized in that, Includes the following steps: (1) Using graphite as a substrate, metal oxide and Li5FeO4 as reaction sources, atomic vapor deposition is used to deposit metal oxide and Li5FeO4 on graphite 1-100 times to obtain graphite precursor material. (2) After uniformly dispersing the graphite precursor material in the resin solution, spray drying is performed, followed by heat treatment at 800-1200℃ for 1-6 hours, and finally high-temperature graphitization is performed to obtain the graphite composite material.

3. The preparation method according to claim 2, characterized in that, In step (1), each atomic layer deposition is performed in the order of one metal oxide and one Li5FeO4.

4. The preparation method according to claim 3, characterized in that, In step (1), the deposition time of each metal oxide is 1-3s, and the deposition time of each Li5FeO4 is 0.5-1s.

5. The preparation method according to claim 2, characterized in that, In the atomic vapor deposition of step (1), the reaction temperature is 100-200℃, the vacuum degree is 1-10 torr, after deposition, nitrogen gas is pulsed and cleaned for 4s, then water vapor is pulsed for 0.1s, and then the next deposition is carried out.

6. The preparation method according to claim 2, characterized in that, In step (2), the mass ratio of graphite precursor material to resin is 100:5-20.

7. The preparation method according to claim 6, characterized in that, The mass-to-volume ratio of resin to solvent in the resin solution is 1-10g:100ml.

8. The preparation method according to claim 7, characterized in that, The resin mentioned is one of phenolic resin, furfural resin, and epoxy resin; The solvent is one of N-methylpyrrolidone, cyclohexane, and carbon tetrachloride.

Images