A negative electrode composite material, a preparation method therefor, and use thereof

Abstract

The application discloses a negative electrode composite material and a preparation method and application thereof, and belongs to the technical field of battery materials.The negative electrode composite material comprises a negative electrode active material and graphite; the negative electrode active material comprises a silicon-based material, a soft carbon coating layer coated on the surface of the silicon-based material, and a polymer coating layer coated on the outer surface of the soft carbon coating layer; the polymer coating layer is obtained by esterification reaction grafting of carboxyl in a viologen compound and hydroxyl on the surface of the silicon-based material and hydroxyl on the surface of the soft carbon coating layer; the polymer in the polymer coating layer has a self-polymerization reaction in the charging and discharging cycle process of an electrochemical device, and has a self-repairing performance; and the negative electrode composite material provided by the application improves the cycle performance of a secondary battery by coating the viologen compound containing carboxyl on the outer surface of the silicon monoxide with the soft carbon coating to form the polymer coating layer.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a negative electrode composite material, its preparation method, and its application. Background Technology

[0002] The theoretical specific capacity of silicon anodes is 4200 mAh / g, which is more than 10 times that of graphite. However, the huge volume expansion effect of silicon anode materials results in unsatisfactory cycle life of power batteries. Silicon suboxide is a more ideal silicon-based anode material, thanks to its dispersed silicon grain structure. Silicon suboxide has a significant advantage in cycle performance compared to pure silicon anodes. However, the required cycle life of 1000-2000 cycles for power batteries is continuously driving researchers to improve the coating performance of silicon suboxide.

[0003] Dyes and Pigment, also known as violetin, is an N,N'-disubstituted 4,4'-bipyridine cationic salt. It is a classic organic redox substance with a stable oxidation state, excellent electron acceptability, and good redox properties, thus it is widely used in electrochromic devices, energy storage, and other fields. Furthermore, its conjugated structure enables electron transport. Moreover, according to relevant literature (Dyes and Pigment. Volume 33, Issue 2, February 1997, Pages 167-172), violetin molecules can undergo head-to-tail dimerization under voltage stimulation.

[0004] Therefore, it is necessary to develop a composite material that uses viologen compounds to coat silicon suboxide in order to further improve the cycle performance of secondary batteries. Summary of the Invention

[0005] This invention provides a negative electrode composite material, its preparation method, and its application. By coating a viologen compound containing carboxyl groups onto the outer surface of silicon suboxide with soft carbon coating, the carboxyl groups in the viologen compound undergo esterification with the hydroxyl groups in the silicon suboxide and the soft carbon coating layer to form a polymer coating layer, thereby improving the battery's cycle performance. Simultaneously, during battery charge-discharge cycles, the viologen compound molecules can undergo self-polymerization and possess self-healing properties, which helps maintain the integrity of the polymer coating layer on the silicon suboxide surface, thus ensuring the battery's cycle stability. Furthermore, the negative electrode composite material preparation method provided by this invention is simple, easy to operate, and suitable for commercial production.

[0006] In a first aspect, embodiments of the present invention provide a negative electrode composite material, the negative electrode composite material comprising: a negative electrode active material and graphite;

[0007] The negative electrode active material includes: a silicon-based material, a soft carbon coating layer covering the surface of the silicon-based material, and a polymer coating layer covering the outer surface of the soft carbon coating layer;

[0008] The polymer coating layer is obtained by grafting the carboxyl groups in the carboxyl-containing viologen compound with the hydroxyl groups on the surface of the silicon-based material and the hydroxyl groups on the surface of the soft carbon coating layer through an esterification reaction.

[0009] The polymer in the polymer coating layer undergoes a self-polymerization reaction during the charge-discharge cycle of the electrochemical device.

[0010] The polymer in the polymer coating layer has self-healing properties during the charge-discharge cycle of the electrochemical device.

[0011] The general structural formula of the carboxyl-containing viologen compound is:

[0012] Wherein, R is an alkyl functional group and its derivatives or a phenyl functional group and its derivatives; X - Including one or more of the following: nitrate ions, halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and trifluoromethanesulfonate ions.

[0013] Preferably, the specific capacity of the negative electrode composite material is between 595mAh / g and 605mAh / g;

[0014] The negative electrode active material exhibits infrared absorption in the 1720-1740 cm⁻¹ range. -1 It exhibits a strong C=O absorption peak at 1000-1300 cm⁻¹. -1 It has a C-O-C absorption peak.

[0015] Preferably, the silicon-based material is an electrochemically active powder material, specifically including one or more of silicon suboxide, modified silicon suboxide, or doped silicon suboxide;

[0016] The carboxyl-containing viologen compounds specifically include: 1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine dinitrate, N,N'-bis(terebenzoic acid)-4,4'-bipyridine dichloride, 1,1'-bis(4-carboxy-phenylmethylene)-4,4'-bipyridine dichloride, and 1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine dibromide.

[0017] Preferably, the soft carbon coating layer accounts for 3%-12% of the mass percentage of the silicon-based material;

[0018] The carboxyl-containing viologen compound accounts for 1%-5% of the mass percentage of the silicon-based material containing the soft carbon coating.

[0019] Secondly, embodiments of the present invention provide a method for preparing the negative electrode composite material described in the first aspect above, the method comprising:

[0020] Silicon-based materials are coated with a soft carbon layer by vapor phase coating, and then the silicon-based materials with soft carbon coating are screened to obtain anode material precursors.

[0021] The precursor of the anode material is dispersed in the reaction solvent water, heated to 80℃-120℃, and then a viologen compound containing a carboxyl group is added. The mixture is stirred and reacted for 10-20 hours. After cooling to room temperature, it is spray-dried and graded and sieved to obtain the anode active material.

[0022] The negative electrode active material and graphite are combined according to a set specific capacity to obtain a negative electrode composite material.

[0023] The general structural formula of the carboxyl-containing viologen compound is as follows:

[0024] Wherein, R is an alkyl functional group and its derivative or a phenyl functional group and its derivative; X- includes one or more of the following: nitrate ion, halide ion, tetrafluoroborate ion, hexafluorophosphate ion, and trifluoromethanesulfonate ion.

[0025] Preferably, the silicon-based material is an electrochemically active powder material, specifically including one or more of silicon suboxide, modified silicon suboxide, or doped silicon suboxide;

[0026] The carboxyl-containing viologen compounds specifically include: 1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine dinitrate, N,N'-bis(terebenzoic acid)-4,4'-bipyridine dichloride, 1,1'-bis(4-carboxyphenylmethylene)-4,4'-bipyridine dichloride, and 1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine dibromide;

[0027] The mass ratio of the negative electrode material precursor to the carboxyl-containing viologen compound is 19:1-99:1.

[0028] Preferably, the specific capacity of the negative electrode active material is between 1500 mAh / g and 1750 mAh / g;

[0029] The negative electrode active material and graphite are compounded according to the set specific capacity as follows: according to the set specific capacity of the negative electrode composite material between 595mAh / g and 605mAh / g, the negative electrode active material and graphite are weighed and placed in a mixer and stirred evenly.

[0030] Preferably, the heating temperature is 90°C; and the stirring reaction time is 12 hours.

[0031] The vapor phase coating method includes: placing the silicon-based material in a rotary furnace under an argon atmosphere, heating it to 700℃-1000℃, introducing a mixed gas source for vapor phase coating, holding it at that temperature for 1 hour to 6 hours, then turning off the mixed gas source and cooling it to room temperature to obtain the silicon-based material with a soft carbon coating layer.

[0032] The mixed gas source includes: an inert gas and an organic gas source;

[0033] The volume ratio of the inert gas to the organic gas source is 1:10-10:1;

[0034] The inert gas includes nitrogen, helium, or argon.

[0035] The organic gas source includes one or more of methane, ethylene, acetylene, propylene, or propane.

[0036] Thirdly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising the negative electrode composite material described in the first aspect above.

[0037] Fourthly, embodiments of the present invention provide a secondary battery, the secondary battery comprising the negative electrode sheet described in the third aspect above.

[0038] This invention provides a negative electrode composite material, its preparation method, and its application. By coating a viologen compound containing carboxyl groups onto the outer surface of silicon suboxide with soft carbon coating, the carboxyl groups in the viologen compound undergo esterification with the hydroxyl groups in the silicon suboxide and the soft carbon coating layer to form a polymer coating layer, thereby improving the battery's cycle performance. Simultaneously, during battery charge-discharge cycles, the viologen compound molecules can undergo self-polymerization and possess self-healing properties, which helps maintain the integrity of the polymer coating layer on the silicon suboxide surface, thus ensuring the battery's cycle stability. Furthermore, the negative electrode composite material preparation method provided by this invention is simple, easy to operate, and suitable for commercial production. Attached Figure Description

[0039] The technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0040] Figure 1 This is a flowchart of the preparation method of the negative electrode composite material provided in the embodiments of the present invention.

[0041] Figure 2 This is a flowchart of assembling a battery using a negative electrode composite material, as provided in an embodiment of the present invention. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0043] This invention provides a negative electrode composite material, which includes: a negative electrode active material and graphite; the specific capacity of the negative electrode composite material is between 595mAh / g and 605mAh / g.

[0044] The negative electrode active material includes: a silicon-based material, a soft carbon coating layer covering the surface of the silicon-based material, and a polymer coating layer covering the outer surface of the soft carbon coating layer; the negative electrode active material exhibits infrared absorption in the 1720-1740 cm⁻¹ infrared spectrum. -1 It exhibits a strong C=O absorption peak at 1000-1300 cm⁻¹. -1 The presence of a C-O-C absorption peak indicates that its surface has a polymer coating layer.

[0045] Specifically, the soft carbon coating is formed on the outer surface of silicon-based material particles by vapor phase coating. The soft carbon coating accounts for 3%-12% of the mass of the silicon-based material, preferably 3%-9%.

[0046] The polymer coating layer in the negative electrode active material is obtained by grafting carboxyl groups from a carboxyl-containing viologen compound with hydroxyl groups on the surface of the silicon-based material and the surface of the soft carbon coating layer through an esterification reaction. The polymer in the polymer coating layer undergoes self-polymerization during the charge-discharge cycle of the electrochemical device, and also exhibits self-repairing properties during discharge cycles after polymer chain breakage. The carboxyl-containing viologen compound accounts for 1%-5% of the mass of the silicon-based material containing the soft carbon coating layer, preferably 1%-3%. The general structural formula of the carboxyl-containing viologen compound is:

[0047] Where R is an alkyl functional group and its derivatives or a phenyl functional group and its derivatives; X - Including one or more of the following: nitrate ions, halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and trifluoromethanesulfonate ions.

[0048] This invention provides a method for preparing the above-mentioned negative electrode composite material, such as... Figure 1 As shown, the preparation steps specifically include:

[0049] Step 110: The silicon-based material is coated with a soft carbon layer by vapor phase coating. Then the silicon-based material with soft carbon coating is sieved to obtain the anode material precursor.

[0050] Among them, silicon-based materials are electrochemically active powder materials, specifically including one or more of silicon suboxide, modified silicon suboxide, or doped silicon suboxide;

[0051] The specific method of vapor phase coating is as follows: Under an argon atmosphere, the silicon-based material is placed in a rotary furnace and heated to 700℃-1000℃. A mixed gas source is introduced for vapor phase coating. After holding at this temperature for 1 hour to 6 hours, the mixed gas source is turned off and the temperature is lowered to room temperature, thus obtaining a silicon-based material with a soft carbon coating layer. The mixed gas source includes an inert gas and an organic gas source. The volume ratio of the inert gas to the organic gas source is 1:10-10:1. The inert gas includes nitrogen, helium, or argon. The organic gas source includes one or more of methane, ethylene, acetylene, propylene, or propane.

[0052] Step 120: Disperse the negative electrode material precursor in the reaction solvent water, heat to 80℃-120℃, preferably 90℃, then add a carboxyl-containing viologen compound, stir and react for 10-20 hours, cool to room temperature and spray dry, and obtain the negative electrode active material after grading and sieving.

[0053] The mass ratio of the negative electrode material precursor to the carboxyl-containing viologen compound is 19:1-99:1, preferably 32:1-99:1;

[0054] The general structural formula of viologen compounds containing carboxyl groups is:

[0055] Where R is an alkyl functional group and its derivatives or a phenyl functional group and its derivatives; X - Including one or more of the following: nitrate ions, halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and trifluoromethanesulfonate ions.

[0056] Specifically, it includes:

[0057] The structural formula of dinitrile-1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine is:

[0058]

[0059] dichloro-N,N'-bis(terebenzoic acid)-4,4'-bipyridine, with the following structural formula:

[0060]

[0061] 1,1'-bis(4-carboxy-phenylmethylene)-4,4'-bipyridine dichloride, with the following structural formula:

[0062]

[0063] Dibromo-1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine, with the following structural formula:

[0064]

[0065] In the preferred embodiment, the heating temperature is 90°C and the stirring reaction time is 12 hours.

[0066] Step 130: Combine the negative electrode active material and graphite according to the set specific capacity to obtain the negative electrode composite material.

[0067] The specific capacity of the prepared negative electrode active material is between 1500 mAh / g and 1750 mAh / g;

[0068] The negative electrode active material and graphite are compounded according to the set specific capacity as follows: according to the set specific capacity of the negative electrode composite material between 595mAh / g and 605mAh / g, the negative electrode active material and graphite are weighed and placed in a mixer and stirred evenly.

[0069] The above-mentioned negative electrode composite material in the embodiments of the present invention can be used as a negative electrode active material in a negative electrode sheet, and the negative electrode sheet can be applied in a secondary battery.

[0070] The steps for preparing negative electrode sheets and assembling batteries using the negative electrode composite material provided in the embodiments of the present invention are as follows: Figure 2 As shown, it specifically includes:

[0071] Step 210, preparing the negative electrode sheet, the method includes: weighing the negative electrode material composite, conductive additive, and binder according to the required proportions, and preparing a slurry in a slurry mixer at room temperature. The prepared slurry is uniformly coated onto the negative electrode and the fluid, dried in a forced-air drying oven, cut into electrode sheets, and vacuum-dried in a vacuum drying oven. The dried electrode sheets are then immediately transferred to a glove box for later use in battery assembly.

[0072] Step 220: Prepare the positive electrode sheet. The method includes: mixing the positive active material, conductive agent, and binder in the required proportions, adding solvent, and stirring evenly under vacuum to obtain a positive slurry. The positive slurry is then uniformly coated onto a positive current collector and dried to obtain the positive electrode sheet with the positive material layer.

[0073] Step 230, Assemble the secondary battery: Assemble the battery according to the following order: positive electrode shell + positive electrode + separator + negative electrode + gasket + spring contact + negative electrode shell; before assembling the battery, drop 100ul of electrolyte onto both the negative electrode and the positive electrode.

[0074] The selection of the separator and electrolyte is not specifically limited here, as long as they meet the requirements for the use of secondary batteries.

[0075] In this embodiment, a secondary battery assembled using the negative electrode sheet prepared from the above-mentioned negative electrode composite material can undergo self-polymerization of viologen compound molecules during the battery charge-discharge cycle, and has self-healing properties, which helps maintain the integrity of the polymer coating layer on the silicon suboxide surface, thereby ensuring the cycle stability of the battery.

[0076] To better understand the technical solution provided by this invention, the preparation process and characteristics of the negative electrode composite material of this invention are illustrated below with several specific examples.

[0077] Example 1

[0078] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0079] 1) Silicon suboxide was treated at 850°C in a mixed gas atmosphere (nitrogen:acetylene volume ratio of 2:4) for 4 hours to achieve soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was sieved to obtain the precursor of the anode material.

[0080] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 90℃, then add 20 g of dinitrate-1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain negative electrode active material after grading and sieving.

[0081] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0082] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested.

[0083] Preparation of the negative electrode sheet: The negative electrode material composite, conductive additive carbon black, and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 ratio) are weighed according to a mass ratio of 95:2:3. A slurry is prepared in a pulping machine at room temperature. The prepared slurry is evenly coated onto copper foil. After drying in a forced-air drying oven at 50°C for 2 hours, it is cut into 8×8mm electrode sheets and vacuum-dried in a vacuum drying oven at 100°C for 10 hours. The dried electrode sheets are then immediately transferred to a glove box for use in battery assembly.

[0084] Preparation of the positive electrode sheet: Lithium cobalt oxide (LiCoO2), acetylene black (conductive agent), and polyvinylidene fluoride (PVDF) (binder) are mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto one surface of an aluminum foil current collector and dried to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material.

[0085] Assemble the secondary battery: Assemble the electrochemical device according to the following steps: positive electrode shell + positive electrode + separator + negative electrode + gasket + spring sheet + negative electrode shell; before assembling the battery, drop 100 μL of electrolyte onto each of the negative electrode and the positive electrode. The electrolyte is a dispersion of 1 mole of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1). The separator can be one of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer composite membrane thereof.

[0086] The selection of diaphragm and electrolyte is not specifically limited here.

[0087] The secondary battery assembled in this embodiment was tested.

[0088] Test method: Constant current charge and discharge mode test was performed using a charge and discharge instrument. At 25℃, the discharge cutoff voltage was 0.005V and the charge cutoff voltage was 1.5V. The first week of charge and discharge test was conducted at a current density of C / 10, and the second week of discharge test was conducted at a current density of C / 10.

[0089] The specific capacity of the negative electrode sheet, as well as the battery's first-cycle efficiency and capacity retention after 500 cycles, are detailed in Table 1.

[0090] Example 2

[0091] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0092] 1) Silicon suboxide was treated for 4 hours in a mixed gas atmosphere (nitrogen:natural gas:acetylene volume ratio of 4:2:1) at 1000℃ to perform soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was screened to obtain the precursor of the anode material.

[0093] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 80℃, then add 20 g of dinitrate-1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain negative electrode active material after grading and sieving.

[0094] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0095] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0096] Example 3

[0097] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0098] 1) Silicon suboxide was treated for 3 hours in a mixed gas atmosphere (nitrogen:propylene:acetylene volume ratio of 3:2:1) at 900℃ to perform soft carbon gas phase coating, and then the silicon-based material containing the soft carbon coating layer was screened to obtain the precursor of the anode material.

[0099] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 90℃, then add 32 g of dichloride-N,N'-bis(terebenzoic acid)-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain negative electrode active material after grading and sieving.

[0100] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0101] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0102] Example 4

[0103] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0104] 1) Silicon suboxide was treated at 800°C in a mixed gas atmosphere (nitrogen:propylene volume ratio of 3:3) for 3.5 hours to achieve soft carbon vapor phase coating. Then, the silicon-based material containing the soft carbon coating layer was sieved to obtain the precursor of the anode material.

[0105] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 120℃, then add 18 g of dibromo-1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine, stir and react for 10 hours, cool to room temperature and spray dry, and obtain the negative electrode active material after grading and sieving.

[0106] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0107] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0108] Example 5

[0109] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0110] 1) Silicon suboxide was treated at 920°C in a mixed gas atmosphere (nitrogen:natural gas volume ratio of 1:3) for 3 hours to achieve soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was screened to obtain the precursor of the anode material.

[0111] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 90℃, then add 24 g of dibromide-1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain negative electrode active material after grading and sieving.

[0112] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0113] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0114] Example 6

[0115] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0116] 1) Silicon suboxide was treated for 2 hours in a mixed gas atmosphere (nitrogen:propane volume ratio of 3:1) at 1000℃ to perform soft carbon vapor phase coating, and then the silicon-based material containing the soft carbon coating layer was screened to obtain the precursor of the anode material.

[0117] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 90℃, then add 15 g of 1,1'-bis(4-carboxy-benzylmethyl)-4,4'-bipyridine dichloride, stir and react for 12 hours, cool to room temperature and spray dry, and obtain the negative electrode active material after grading and sieving.

[0118] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0119] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0120] Example 7

[0121] This embodiment provides a preparation process and performance testing method for a negative electrode composite material, and the specific steps are as follows.

[0122] 1) Silicon suboxide was treated for 3 hours in a mixed gas atmosphere (nitrogen:natural gas:propylene volume ratio of 4:2:1) at 980℃ to perform soft carbon gas phase coating, and then the silicon-based material containing the soft carbon coating layer was screened to obtain the precursor of the anode material.

[0123] 2) Disperse 1 kg of negative electrode material precursor in the reaction solvent water, heat to 90℃, then add 40 g of dichloride-N,N'-bis(terebenzoic acid)-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain negative electrode active material after grading and sieving.

[0124] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode composite material.

[0125] The negative electrode sheet was prepared using the negative electrode composite material obtained in this embodiment, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0126] To better illustrate the effects of the embodiments of the present invention, comparative examples 1-3 are compared with example 1.

[0127] Comparative Example 1

[0128] This comparative example provides a preparation process and performance testing of a negative electrode material. The difference from Example 1 is that it uses a viologen compound that does not contain carboxyl groups. The specific steps are as follows.

[0129] 1) Silicon suboxide was treated at 850°C in a mixed gas atmosphere (nitrogen:acetylene volume ratio of 2:4) for 4 hours to achieve soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was sieved to obtain the precursor material.

[0130] 2) Disperse 1 kg of precursor material in water, heat to 90 °C, then add 20 g of dibromo-1,1'-diethyl-4,4'-bipyridine, stir and react for 12 hours, cool to room temperature and spray dry, and obtain the negative electrode active material after grading and sieving.

[0131] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode material.

[0132] The negative electrode material prepared in this comparative example was used to prepare a negative electrode sheet, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0133] Comparative Example 2

[0134] This comparative example provides a preparation process and performance testing of a negative electrode material. The difference from Example 1 is that viologen compound is not used. The specific steps are as follows.

[0135] 1) Silicon suboxide was treated at 850°C in a mixed gas atmosphere (nitrogen:acetylene volume ratio of 2:4) for 4 hours to achieve soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was sieved to obtain the precursor of the anode material.

[0136] 2) The negative electrode material precursor is graded and sieved to obtain the negative electrode active material.

[0137] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode material.

[0138] The negative electrode material prepared in this comparative example was used to prepare a negative electrode sheet, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0139] Comparative Example 3

[0140] This comparative example provides a preparation process and performance test of a negative electrode material. The difference from Example 1 is that no heat treatment was performed after mixing with a carboxyl-containing viologen compound. The specific steps are as follows.

[0141] 1) Silicon suboxide was treated at 850°C in a mixed gas atmosphere (nitrogen:acetylene volume ratio of 2:4) for 4 hours to achieve soft carbon gas phase coating. Then, the silicon-based material containing the soft carbon coating layer was sieved to obtain the precursor of the anode material.

[0142] 2) Disperse 1 kg of negative electrode material precursor in water, then add 20 g of dinitrate-1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine. After uniform dispersion, spray dry and then grade and sieve to obtain negative electrode active material.

[0143] 3) Weigh the negative electrode active material and graphite according to the requirement of 600mAh / g capacity, put them in a mixer and stir evenly to obtain the negative electrode material.

[0144] The negative electrode material prepared in this comparative example was used to prepare a negative electrode sheet, and the battery was assembled and tested. The specific process was the same as in Example 1, and the test results are shown in Table 1.

[0145] Table 1 shows the specific capacity of the negative electrode sheets prepared in Examples 1-7 and Comparative Examples 1-3, as well as the first-cycle efficiency and capacity retention rate of the prepared batteries after 500 cycles.

[0146]

[0147]

[0148] Table 1

[0149] As can be seen from the comparison of test data in Table 1, the battery prepared by the negative electrode composite material of Examples 1-7 has a much higher cycle capacity retention rate after 500 cycles than the battery prepared by the negative electrode material of Comparative Examples 1-3. This is because Examples 1-7 of the present invention use viologen compounds containing carboxyl groups, which are grafted with silicon suboxide through esterification reaction to form a polymer coating layer under electrochemical cycling, effectively improving the cycle performance.

[0150] Example 1 is compared with Comparative Examples 1-3 for illustration. The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not use a viologen compound containing carboxyl groups. Although it could also form a polymer coating layer, the polymer coating layer of Comparative Example 1 did not have good adhesion to the silicon suboxide matrix due to the lack of grafting of carboxyl and hydroxyl groups, resulting in unsatisfactory cycle performance. The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 did not use a viologen compound, and its silicon suboxide surface did not have a polymer coating layer, resulting in faster degradation of cycle performance. The difference between Comparative Example 3 and Example 1 is that after adding a viologen compound containing carboxyl groups and mixing, no heat treatment was performed, making it difficult for esterification to occur. The carboxyl and hydroxyl groups did not undergo esterification grafting, so Comparative Example 3 did not show significant improvement in coating.

[0151] Generally, the specific capacity of silicon suboxide anode materials in traditional power batteries is 400mAh / g-420mAh / g, and the capacity retention rate is about 80% after 1000-2000 cycles. Compared with traditional power batteries, the anode composite materials prepared in Examples 1-7 of this invention still have a cycle retention rate of 93%-95% after 500 cycles. In terms of cycle life, it is equivalent to the cycle life of traditional power batteries after 1000-2000 cycles. However, the specific capacity of the anode composite material in the embodiments of this invention is 600mAh / g, which has a higher energy density. Therefore, it can be considered that under the same cycle life, the anode composite material in the embodiments of this invention has a higher energy density and its performance is better than that of traditional power batteries.

[0152] This invention provides a negative electrode composite material, its preparation method, and its application. By coating a viologen compound containing carboxyl groups onto the outer surface of silicon suboxide with soft carbon coating, the carboxyl groups in the viologen compound undergo esterification with the hydroxyl groups in the silicon suboxide and the soft carbon coating layer to form a polymer coating layer, thereby improving the battery's cycle performance. Simultaneously, during battery charge-discharge cycles, the viologen compound molecules can undergo self-polymerization and possess self-healing properties, which helps maintain the integrity of the polymer coating layer on the silicon suboxide surface, thus ensuring the battery's cycle stability. Furthermore, the negative electrode composite material preparation method provided by this invention is simple, easy to operate, and suitable for commercial production.

[0153] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode composite material for an electrochemical device, characterized in that, The negative electrode composite material includes: a negative electrode active material and graphite; The negative electrode active material includes: a silicon-based material, a soft carbon coating layer covering the surface of the silicon-based material, and a polymer coating layer covering the outer surface of the soft carbon coating layer; The polymer coating layer is obtained by grafting the carboxyl groups in the carboxyl-containing viologen compound with the hydroxyl groups on the surface of the silicon-based material and the hydroxyl groups on the surface of the soft carbon coating layer through an esterification reaction. The polymer in the polymer coating layer undergoes a self-polymerization reaction during the charge-discharge cycle of the electrochemical device. The polymer in the polymer coating layer has self-healing properties during the charge-discharge cycle of the electrochemical device. The general structural formula of the carboxyl-containing viologen compound is: Wherein, R is an alkyl functional group and its derivatives or a phenyl functional group and its derivatives; X - Including one or more of the following: nitrate ions, halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and trifluoromethanesulfonate ions.

2. The negative electrode composite material according to claim 1, characterized in that, The specific capacity of the negative electrode composite material is between 595 mAh / g and 605 mAh / g; The negative electrode active material exhibits infrared absorption in the 1720-1740 cm⁻¹ range. -1 It exhibits a strong C=O absorption peak at 1000-1300 cm⁻¹. -1 It has a C-O-C absorption peak.

3. The negative electrode composite material according to claim 1, characterized in that, The silicon-based material is an electrochemically active powder material, specifically including one or more of silicon suboxide, modified silicon suboxide, or doped silicon suboxide; The carboxyl-containing viologen compounds specifically include: 1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine dinitrate, N,N'-bis(terebenzoic acid)-4,4'-bipyridine dichloride, 1,1'-bis(4-carboxy-phenylmethylene)-4,4'-bipyridine dichloride, and 1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine dibromide.

4. The negative electrode composite material according to claim 1, characterized in that, The soft carbon coating layer accounts for 3%-12% of the mass percentage of the silicon-based material; The carboxyl-containing viologen compound accounts for 1%-5% of the mass percentage of the silicon-based material with a soft carbon coating.

5. A method for preparing the negative electrode composite material according to any one of claims 1-4, characterized in that, The preparation method includes: Silicon-based materials are coated with a soft carbon layer by vapor phase coating, and then the silicon-based materials with soft carbon coating are screened to obtain anode material precursors. The precursor of the anode material is dispersed in the reaction solvent water, heated to 80℃-120℃, and then a viologen compound containing a carboxyl group is added. The mixture is stirred and reacted for 10-20 hours. After cooling to room temperature, it is spray-dried and graded and sieved to obtain the anode active material. The negative electrode active material and graphite are combined according to a set specific capacity to obtain a negative electrode composite material. The general structural formula of the carboxyl-containing viologen compound is as follows: Wherein, R is an alkyl functional group and its derivatives or a phenyl functional group and its derivatives; X - Including one or more of the following: nitrate ions, halide ions, tetrafluoroborate ions, hexafluorophosphate ions, and trifluoromethanesulfonate ions.

6. The preparation method according to claim 5, characterized in that, The silicon-based material is an electrochemically active powder material, specifically including one or more of silicon suboxide, modified silicon suboxide, or doped silicon suboxide; The carboxyl-containing viologen compounds specifically include: 1,1'-bis(3,5-dicarboxyphenylmethylene)-4,4'-bipyridine dinitrate, N,N'-bis(terebenzoic acid)-4,4'-bipyridine dichloride, 1,1'-bis(4-carboxyphenylmethylene)-4,4'-bipyridine dichloride, and 1,1'-bis(4'-carboxy-(1,1'-biphenyl)-4-methylene)-4,4'-bipyridine dibromide; The mass ratio of the negative electrode material precursor to the carboxyl-containing viologen compound is 19:1-99:

1.

7. The preparation method according to claim 5, characterized in that, The specific capacity of the negative electrode active material is between 1500mAh / g and 1750mAh / g; The negative electrode active material and graphite are compounded according to the set specific capacity as follows: according to the set specific capacity of the negative electrode composite material between 595mAh / g and 605mAh / g, the negative electrode active material and graphite are weighed and placed in a mixer and stirred evenly.

8. The preparation method according to claim 5, characterized in that, The heating temperature is 90°C; the stirring reaction time is 12 hours; The vapor phase coating method includes: placing the silicon-based material in a rotary furnace under an argon atmosphere, heating it to 700℃-1000℃, introducing a mixed gas source for vapor phase coating, holding it at that temperature for 1 hour to 6 hours, then turning off the mixed gas source and cooling it to room temperature to obtain the silicon-based material with a soft carbon coating layer. The mixed gas source includes: an inert gas and an organic gas source; The volume ratio of the inert gas to the organic gas source is 1:10-10:1; The inert gas includes nitrogen, helium, or argon. The organic gas source includes one or more of methane, ethylene, acetylene, propylene, or propane.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode composite material described in any one of claims 1-4.

10. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet as described in claim 9.

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