A modified hard carbon negative electrode sheet and its preparation method and application

Abstract

A modified hard carbon negative electrode plate and its preparation method and application belong to the technical field of secondary sodium ion batteries. The specific scheme is as follows: the modified hard carbon negative electrode plate is obtained by in-situ surface treatment of the hard carbon negative electrode plate with an interfacial modifier, the interfacial modifier is an alcohol-based solution or an ether-based solution of trimethoxysilane and a compound with the molecular formula (R1)2BR2, R1 is a hydrolyzable methoxy, ethoxy, aminomethoxy and aminoethoxy functional group, and R2 is a non-hydrolyzable, hydrophobic hydrocarbon group, benzene ring, or ester functional group; the present invention constructs a molecular network interface on the surface of the hard carbon negative electrode through the hydrolysis and condensation reaction of trimethoxysilane and (R1)2BR2, forming a uniform and stable SEI film, effectively improving the compatibility of the hard carbon negative electrode with a carbonate-based electrolyte. The secondary sodium ion battery prepared by the modified hard carbon negative electrode has good first coulombic efficiency, cycle stability and rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary sodium ion batteries, and in particular relates to a modified hard carbon negative electrode plate and a preparation method and application thereof. Background Art

[0002] In recent years, sodium ion batteries have been widely used in various electronic products, low-speed electric vehicles, grid energy storage and other fields due to their abundant sodium resources, low cost and good low-temperature performance. Hard carbon materials have high specific capacity (300-350mAh / g) and low operating voltage (~0.1Vv.Na / Na + ) and low cost, and thus has good commercial prospects. However, hard carbon anodes have poor compatibility with commercial carbonate-based electrolytes, and the SEI film they form is unstable. This results in low first coulombic efficiency, poor cycling stability, and low energy density in sodium-ion batteries using hard carbon anodes and carbonate-based electrolytes.

[0003] Most hard carbon materials are obtained by calcining materials such as anthracite and biomass. This inevitably leads to the presence of a large number of oxygen-containing functional groups (such as hydroxyl and carboxyl groups) and defects on the surface of the hard carbon materials. These oxygen-containing functional groups and defects will adsorb carbonate electrolyte solvent molecules, induce the accumulation of solvent molecule decomposition products on the negative electrode surface, and capture active sodium ions, thereby causing the above-mentioned problems. Therefore, it is particularly important to improve the first coulombic efficiency, cycle life and energy density of sodium-ion batteries by adjusting the surface properties of the hard carbon negative electrode and improving its compatibility with carbonate electrolytes. Summary of the Invention

[0004] To address the problems presented in the prior art, the present invention provides a modified hard carbon anode electrode, its preparation method, and its application. Through the self-assembly of an interfacial modifier on the surface of the hard carbon anode, a molecular network interface is constructed on the surface of the hard carbon anode. This effectively passivates the inherent oxygen-containing functional groups and defects on the hard carbon surface, improving the compatibility of the hard carbon anode with carbonate-based electrolytes.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A modified hard carbon negative electrode plate is obtained by in-situ surface treatment of a hard carbon negative electrode plate with an interfacial modifier, wherein the interfacial modifier is an alcohol-based solution or an ether-based solution of trimethoxysilane and a compound with the molecular formula (R1)2BR2; wherein R1 is a hydrolyzable methoxy, ethoxy, aminomethoxy or aminoethoxy functional group, and R2 is a non-hydrolyzable, hydrophobic hydrocarbon group, benzene ring or ester functional group, and the amount of water added to the alcohol-based solution or the ether-based solution is 0.5%-5% of the total mass of the trimethoxysilane and (R1)2BR2.

[0007] Furthermore, the amount of trimethoxysilane added is 5%-20% of the mass of the alcohol-based solvent or ether-based solvent, and the amount of the compound with the molecular formula (R1)2BR2 added is 0.2%-10% of the mass of the alcohol-based solvent or ether-based solvent.

[0008] Furthermore, the compound with the molecular formula (R1)2BR2 includes a combination of one or more borate esters and their derivatives, the alcohol-based solvent includes a combination of one or more methanol, ethanol, propanol, and ethylene glycol, and the ether-based solvent includes a combination of one or more diethyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

[0009] A method for preparing the modified hard carbon negative electrode sheet comprises the following steps:

[0010] Step 1: adding deionized water to an alcohol-based solvent or an ether-based solvent, and then adding trimethoxysilane and a compound with a molecular formula of (R1)2BR2, and mixing them uniformly to obtain an interfacial modifier;

[0011] Step 2: Heat the interface modifier to 30° C.-50° C. and then spray, immerse or coat the hard carbon negative electrode sheet, let it stand and dry to obtain a modified hard carbon negative electrode sheet.

[0012] Furthermore, in step 2, the drying treatment conditions are: vacuum drying at 80° C. for 6-8 hours.

[0013] Furthermore, the total mass of the trimethoxysilane and (R1)2BR2 used is 2%-35% of the mass of the hard carbon active material contained in the treated hard carbon negative electrode sheet.

[0014] An application of the modified hard carbon negative electrode sheet is provided, wherein the modified hard carbon negative electrode sheet is used in a sodium ion battery. The sodium ion battery further comprises an electrolyte, wherein the electrolyte is a carbonate-based electrolyte. The carbonate-based electrolyte comprises a carbonate solvent and a fluorine-containing sodium salt.

[0015] Furthermore, the sodium ion battery also includes a positive electrode, and the positive electrode includes any one of a layered oxide positive electrode, a Prussian blue positive electrode, a polyanion positive electrode and an organic positive electrode.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The hydrolyzable functional groups in trimethoxysilane and the compound with the molecular formula (R1)2BR2 form hydroxyl groups upon hydrolysis. These hydroxyl groups condense with hydroxyl or carboxyl groups on the surface of the hard carbon anode, while also undergoing dehydration condensation. This creates a self-assembled molecular interface layer on the surface of the hard carbon anode, consisting of a combination of Si-O-Si and BOB. Because trimethoxysilane contains three hydrolyzable functional groups, the Si-O-Si network is more likely to connect to the surface of the hard carbon anode, while the BOB network is mixed within the Si-O-Si network. Through the construction of the self-assembled molecular interface layer, the original oxygen-containing functional groups on the surface of the hard carbon anode are consumed, suppressing the side reactions of these highly active functional groups with the carbonate electrolyte. The resulting Si-O-Si and BOB network also enhances the surface strength of the hard carbon anode. Furthermore, the hydrogen atoms on the trimethoxysilane molecules form strong hydrogen bonds with the fluorine-containing sodium salt anions, and the unsaturated boron atoms in the borate esters and their derivatives also strongly adsorb the anions. Together, these atoms induce the enrichment of the fluorine-containing sodium salt on the surface of the hard carbon anode, thereby facilitating the formation of an anion-derived fluorine-boride-rich SEI film and greatly enhancing interfacial stability. Furthermore, the R2 functional group is a hydrophobic group, attached to the molecular network and extending into the electrolyte, preventing trace water in the electrolyte from damaging the surface during the film formation process of the hard carbon anode. Secondary sodium-ion batteries prepared using this modified hard carbon anode exhibit excellent first coulombic efficiency, cycling stability, and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The first charge-discharge curves of the Na||HC half-cells prepared in Example 1(a) and Comparative Example 1(b) at a current density of 50 mA / g;

[0019] Figure 2 Long cycle curves of the Na||HC half-cells prepared in Example 2(a) and Comparative Example 2(b) at a current density of 100 mA / g;

[0020] Figure 3 The first charge-discharge curves of the HC||Prussian blue full battery prepared in Example 3(a) and Comparative Example 3(b) at a current density of 20 mA / g;

[0021] Figure 4 Long cycle curves of HC||Prussian blue full cells prepared in Example 4(a) and Comparative Example 4(b) at a current density of 200 mA / g;

[0022] Figure 5 Rate performance curves of HC||Prussian blue full cells prepared in Example 5(a) and Comparative Example 5(b);

[0023] Figure 6Long cycle curve of the HC||Na4Fe3(PO4)2P2O7 full battery prepared in Example 6 at a current density of 100 mA / g;

[0024] Figure 7 Long cycle curve of the HC||Na4Fe3(PO4)2P2O7 full battery prepared in Comparative Example 6 at a current density of 100 mA / g. DETAILED DESCRIPTION

[0025] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] A modified hard carbon negative electrode and preparation method are provided. First, 0.015 g of deionized water is added to 2 g of methanol solvent, and then 0.2 g of trimethoxysilane and 0.1 g of o-methylcyclohexanol diethanolamine borate are added and mixed uniformly to obtain an interface modifier. The interface modifier is heated to 45°C and then sprayed on the hard carbon negative electrode. The active material loading of the treated hard carbon negative electrode is 10 mg / cm 2 , the treatment area is 100cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 80°C for 8 hours.

[0028] The specific battery assembly process and electrochemical performance test are as follows:

[0029] A CR2025 button half-cell was assembled using a modified hard carbon negative electrode and a sodium metal disc. The electrolyte used was EC / PC / EMC (1:1:4)-NaPF6 (1 mol / L), the electrolyte dosage was 200 μL, and the diaphragm was GF / D, thus obtaining a Na||HC half-cell. The prepared Na||HC half-cell was charged and discharged at a current density of 50 mA / g at room temperature. The experimental results are shown in FIG. Figure 1 As shown in (a), the battery operates normally and the first coulombic efficiency is 82.56%.

[0030] Example 2

[0031] A modified hard carbon negative electrode and preparation method, first adding 0.005g of deionized water to 1g of ether solvent, then adding 0.1g of trimethoxysilane and 0.1g of dimethoxyphenylborane and mixing them evenly to obtain an interface modifier, heating the interface modifier to 45°C and then coating the hard carbon negative electrode. The active material loading of the treated hard carbon negative electrode is 10mg / cm 2 , the treatment area is 60cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 80°C for 8 hours.

[0032] The specific battery assembly process and electrochemical performance test are as follows:

[0033] A CR2025 button half-cell was assembled using a modified hard carbon negative electrode and a sodium metal disc. The electrolyte used was EC / PC / EMC (1:1:4)-NaPF6 (1 mol / L), the electrolyte dosage was 200 μL, and the diaphragm was GF / D, thus obtaining a Na||HC half-cell. The prepared Na||HC half-cell was activated at room temperature at a current density of 50 mA / g, and then subjected to a long cycle charge and discharge test at a current density of 100 mA / g. The experimental results are shown in FIG. Figure 2 As shown in (a), the battery operates normally and the discharge capacity still reaches 266.45mAh / g after 300 cycles.

[0034] Example 3

[0035] A modified hard carbon negative electrode and preparation method, first adding 0.001g of deionized water to 1g of methanol solvent, then adding 0.1g of trimethoxysilane and 0.1g of diethoxyphenylborane, mixing evenly to obtain an interface modifier, heating the interface modifier to 50°C and then spraying it to treat the hard carbon negative electrode. The active material loading of the treated hard carbon negative electrode is 15mg / cm 2 , the treatment area is 60cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 70°C for 8 hours.

[0036] The specific battery assembly process and electrochemical performance test are as follows:

[0037] A modified hard carbon negative electrode was used as the negative electrode, Prussian blue was used as the positive electrode, EC / PC (1:1)-NaFSI (1 mol / L) was used as the electrolyte, the electrolyte dosage was 200 μL, and the GF / D diaphragm was used as the separator to assemble a CR2025 type HC||Prussian blue button full battery. The prepared HC||Prussian blue full battery was charged and discharged at a current density of 20 mA / g at room temperature. The experimental results are shown in Figure 2. Figure 3 As shown in (a), the battery operates normally and the first coulombic efficiency is 94.5%.

[0038] Example 4

[0039] A modified hard carbon negative electrode plate and preparation method are provided. First, 0.005 g of deionized water is added to 1 g of ethylene glycol dimethyl ether solvent, and then 0.2 g of trimethoxysilane and 0.1 g of o-methylcyclohexanol diethanolamine borate are added and mixed evenly to obtain an interface modifier. The interface modifier is heated to 35°C and then impregnated into the hard carbon negative electrode plate. The active material loading of the treated hard carbon negative electrode plate is 15 mg / cm 2 , the treatment area is 60cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 80°C for 8 hours.

[0040] The specific battery assembly process and electrochemical performance test are as follows:

[0041] The modified hard carbon negative electrode was used as the negative electrode, Prussian blue was used as the positive electrode, the electrolyte was EC / PC (1:1)-NaFSI (1 mol / L), the electrolyte dosage was 200 μL, and the GF / D diaphragm was used to assemble the CR2025 type HC||Prussian blue button full battery; the prepared HC||Prussian blue full battery was activated at room temperature at a current density of 20 mA / g and then subjected to a long cycle charge and discharge test at a current density of 200 mA / g. The experimental results are shown in FIG. Figure 4 As shown in (a), the battery operates normally and the discharge capacity still reaches 117.32 mAh / g after 80 cycles.

[0042] Example 5

[0043] A modified hard carbon negative electrode and preparation method, first adding 0.01g of deionized water to 1g of ethanol solvent, then adding 0.2g of trimethoxysilane and 0.1g of (4-formylphenyl) dimethyl borate and mixing them uniformly to obtain an interface modifier, and then heating the interface modifier to 40°C and spraying it on the hard carbon negative electrode. The active material loading of the treated hard carbon negative electrode is 15mg / cm 2 , the treatment area is 100cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 80°C for 8 hours.

[0044] The specific battery assembly process and electrochemical performance test are as follows:

[0045] The modified hard carbon negative electrode was used as the negative electrode, Prussian blue was used as the positive electrode, the electrolyte was EC / DEC (1:1)-NaPF6 (1 mol / L), the electrolyte dosage was 200 μL, and the GF / D diaphragm was used to assemble the CR2025 type HC||Prussian blue button full battery. The prepared HC||Prussian blue full battery was subjected to rate charge and discharge tests at room temperature at current densities of 20 mA / g, 100 mA / g, 200 mA / g, 400 mA / g and 600 mA / g, respectively. The experimental results are shown in Figure 2. Figure 5 As shown in (a), the battery operates normally and the discharge capacity still reaches 60-80mAh / g at a current density of 600mA / g.

[0046] Example 6

[0047] A modified hard carbon negative electrode and preparation method are provided. First, 0.002 g of deionized water is added to 0.5 g of tetrahydrofuran solvent, and then 0.05 g of trimethoxysilane and 0.05 g of diethyl (4-formylphenyl) borate are added and mixed uniformly to obtain an interface modifier. The interface modifier is heated to 40° C. and then sprayed on the hard carbon negative electrode. The active material loading of the treated hard carbon negative electrode is 5 mg / cm 2 , the treatment area is 100cm 2 After standing for 30 minutes, the modified hard carbon negative electrode was obtained by vacuum drying at 80°C for 8 hours.

[0048] The specific battery assembly process and electrochemical performance test are as follows:

[0049] The modified hard carbon negative electrode is used as the negative electrode, Na4Fe3(PO4)2P2O7 is used as the positive electrode, and the electrolyte is

[0050] EC / PC / DEC (1:1:4)-NaPF6 (1 mol / L), the electrolyte dosage was 200 μL, and the GF / D diaphragm was used to assemble the CR2025 type HC||Na4Fe3(PO4)2P2O7 button full battery. The prepared HC||Na4Fe3(PO4)2P2O7 full battery was subjected to a long cycle charge and discharge test at room temperature at a current density of 100 mA / g. The experimental results are shown in Figure 2. Figure 6 As shown in the figure, the battery operates normally and the discharge capacity still reaches 75.82mAh / g after 100 cycles.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 1. The CR2025 type Na||HC half-cell assembled in Comparative Example 1 is subjected to charge and discharge tests at a current density of 50 mA / g at room temperature. The experimental results are shown in FIG. Figure 1As shown in (b), the first coulombic efficiency of the battery is 75.85%.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 2 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 2. The Na||HC half-cell assembled in Comparative Example 2 is activated at a current density of 50 mA / g at room temperature and then subjected to a long cycle charge and discharge test at a current density of 100 mA / g. The experimental results are shown in FIG. Figure 2 As shown in (b), the discharge capacity is 187.34 mAh / g after 100 cycles.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 3 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 3. The CR2025 type HC||Prussian blue button full battery assembled in Comparative Example 3 is subjected to charge and discharge tests at a current density of 20 mA / g at room temperature. The experimental results are shown in FIG. Figure 3 As shown in (b), the first charge and discharge coulombic efficiency is 84.9%.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 4 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 4. The CR2025 type HC||Prussian blue button full battery assembled in Comparative Example 4 was activated at a current density of 20 mA / g at room temperature and then subjected to a long cycle charge and discharge test at a current density of 200 mA / g. The experimental results are shown in FIG. Figure 4 As shown in (b), the discharge capacity of the battery is 98.48 mAh / g after 80 cycles.

[0059] Comparative Example 5

[0060] The difference between this comparative example and Example 5 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 5. The HC||Prussian blue full battery assembled in Comparative Example 5 is subjected to rate charge and discharge tests at room temperature at current densities of 20 mA / g, 100 mA / g, 200 mA / g, 400 mA / g and 600 mA / g, respectively. The experimental results of Comparative Example 5 are shown in FIG. Figure 5 As shown in (b), the discharge specific capacity is less than 60 mAh / g at a current density of 600 mA / g.

[0061] Comparative Example 6

[0062] The difference between this comparative example and Example 6 is that the negative electrode adopts an untreated hard carbon negative electrode, and the rest is the same as Example 6. The HC||Na4Fe3(PO4)2P2O7 full battery assembled in Comparative Example 6 was subjected to a long cycle charge and discharge test at a current density of 100 mA / g at room temperature. The experimental results of Comparative Example 6 are shown in FIG. Figure 7 As shown, the discharge capacity of the battery is 30.61 mAh / g after 100 cycles.

[0063] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A modified hard carbon negative electrode plate, characterized in that: The modified hard carbon negative electrode plate is obtained by in-situ surface treatment of the hard carbon negative electrode plate with an interfacial modifier, wherein the interfacial modifier is an alcohol-based solution or an ether-based solution of trimethoxysilane and a compound with the molecular formula (R1)2BR2; wherein R1 is a hydrolyzable methoxy, ethoxy, aminomethoxy or aminoethoxy functional group, and R2 is a non-hydrolyzable, hydrophobic hydrocarbon group, benzene ring or ester functional group, and the amount of water added to the alcohol-based solution or the ether-based solution is 0.5%-5% of the total mass of trimethoxysilane and (R1)2BR2.

2. The modified hard carbon negative electrode according to claim 1, characterized in that: The added amount of the trimethoxysilane is 5%-20% of the mass of the alcohol-based solvent or the ether-based solvent, and the added amount of the compound with the molecular formula (R1)2BR2 is 0.2%-10% of the mass of the alcohol-based solvent or the ether-based solvent.

3. The modified hard carbon negative electrode according to claim 1, characterized in that: The compound with the molecular formula (R1)2BR2 includes one or more combinations of borate esters and their derivatives, the solvent of the alcohol-based solution includes one or more combinations of methanol, ethanol, propanol, and ethylene glycol, and the solvent of the ether-based solution includes one or more combinations of diethyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

4. A method for preparing a modified hard carbon negative electrode sheet according to claim 1, 2 or 3, characterized in that: The following steps are involved: Step 1: adding deionized water to an alcohol-based solvent or an ether-based solvent, and then adding trimethoxysilane and a compound with a molecular formula of (R1)2BR2, and mixing them uniformly to obtain an interfacial modifier; Step 2: Heat the interface modifier to 30° C.-50° C. and then spray, immerse or coat the hard carbon negative electrode sheet, let it stand and dry to obtain a modified hard carbon negative electrode sheet.

5. The preparation method according to claim 4, characterized in that In step 2, the drying treatment conditions are: vacuum drying at 80° C. for 6-8 hours.

6. The preparation method according to claim 4, characterized in that: The total mass of the trimethoxysilane and (R1)2BR2 used is 2%-35% of the mass of the hard carbon active material contained in the processed hard carbon negative electrode sheet.

7. An application of the modified hard carbon negative electrode sheet according to claim 1, 2 or 3, characterized in that: The modified hard carbon negative electrode plate is used in sodium ion batteries.

8. The use according to claim 7, characterized in that: The sodium ion battery further includes an electrolyte, which is a carbonate-based electrolyte.

9. The use according to claim 8, characterized in that: The carbonate-based electrolyte includes a carbonate solvent and a fluorine-containing sodium salt.

10. The use according to claim 7, characterized in that: The sodium ion battery further comprises a positive electrode, which comprises any one of a layered oxide positive electrode, a Prussian blue positive electrode, a polyanion positive electrode and an organic positive electrode.

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