Sodium-ion battery negative plate, preparation method thereof and sodium-ion battery

Abstract

The invention relates to the technical field of sodium-ion batteries, and discloses a sodium-ion battery negative plate, a preparation method thereof and a sodium-ion battery. On the basis of the total weight of the sodium ion battery negative plate, the content of the hard carbon in the negative plate is 97-99 wt%, and the content of the solid electrolyte membrane is 1-3 wt%. The invention also discloses a preparation method of the sodium ion battery negative electrode plate, and the method comprises the following steps: (1) carrying out compression molding and sintering on the solid electrolyte material to obtain a solid electrolyte target material; (2) performing magnetron sputtering by taking hard carbon as a substrate to obtain a substrate of which the surface is coated with a solid electrolyte membrane; and (3) carrying out heat treatment on the substrate of which the surface is coated with the solid electrolyte membrane. When the negative plate disclosed by the invention is applied to the sodium ion battery, the battery can have higher first efficiency, charge-discharge capacity and cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a negative electrode sheet for a sodium-ion battery, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] Environmental problems such as global warming caused by traditional energy sources are becoming increasingly severe, and it is urgent to develop new clean and renewable energy sources. In the past two decades, lithium-ion batteries (LIBs) have been discovered and widely used in fields such as energy and information conversion and drive. With the increase in the usage of lithium-ion batteries, the price of battery-grade lithium carbonate has also risen, and the cost issue has become an important factor restricting the further development of lithium-ion batteries.

[0003] The properties of sodium are similar to those of lithium, but the cost is lower. Therefore, sodium metal batteries are recognized as one of the most promising alternatives to lithium-ion batteries. Compared with liquid electrolyte sodium-ion batteries, solid-state sodium batteries (SSNBs) have both high energy density, high power density, and excellent safety, and have lower manufacturing costs and maintenance costs.

[0004] Hard carbon is a key component of sodium-ion batteries. Therefore, the preparation of excellent hard carbon negative electrode materials is the key to the development of sodium-ion batteries. Hard carbon is an amorphous carbon that is difficult to graphitize, has a larger interlayer spacing than graphite negative electrodes, has good fast charge and discharge performance, especially excellent low-temperature charge and discharge performance. However, due to the high specific surface area of hard carbon and its porous structure, the first efficiency and specific capacity of the material are low. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems of poor cycle stability, low first efficiency, and low specific capacity when applying hard carbon negative electrode materials to sodium-ion batteries in the prior art, and to provide a negative electrode sheet for a sodium-ion battery, a preparation method thereof, and a sodium-ion battery.

[0006] To achieve the above purpose, in the first aspect of the present invention, a negative electrode sheet for a sodium-ion battery is provided, and the negative electrode sheet for a sodium-ion battery includes: hard carbon and a solid electrolyte film coating the hard carbon.

[0007] In the second aspect of the present invention, a method for preparing a negative electrode sheet for a sodium-ion battery is provided, wherein the method includes:

[0008] (1) Pressing and forming a solid electrolyte material, and sintering to obtain a solid electrolyte target;

[0009] (2) Using hard carbon as a substrate, and performing magnetron sputtering to obtain a substrate with a solid electrolyte film coated on the surface;

[0010] (3) Heat-treat the substrate with a solid electrolyte film coated on its surface to obtain the negative electrode sheet of the sodium-ion battery.

[0011] The third aspect of the present invention provides a negative electrode sheet of a sodium-ion battery prepared by the preparation method provided in the second aspect of the present invention.

[0012] The fourth aspect of the present invention provides a sodium-ion battery, wherein the sodium-ion battery includes a positive electrode, an electrolyte, a separator, and a negative electrode, and the negative electrode includes the negative electrode sheet of the sodium-ion battery of the present invention.

[0013] Through the above technical solutions, the present invention realizes the modification of the negative electrode sheet by coating the solid electrolyte on the surface of the negative electrode sheet. First, the surface of the hard carbon is directly coated with the solid electrolyte material. The electron insulation of the coating layer does not hinder the electron transport inside the electrode, so that the modified hard carbon negative electrode material of the present invention still has good fast charge and discharge performance. Secondly, the material constituting the solid electrolyte film is a doped sodium-based superionic conductor, which has excellent sodium ion conductivity, high thermal stability, chemical / electrochemical stability, and good chemical / electrochemical compatibility with the carbon electrode material. In addition, from Figure 1 the SEM photos of the modified negative electrode sheet prepared in Example 1 shown, it can be seen that the solid electrolyte film coating the surface of the negative electrode sheet is uniform, dense, and has a thickness of 10-100 nm. When the modified negative electrode material is applied to a sodium-ion battery, the solid electrolyte film can reduce the contact between the electrolyte and the negative electrode sheet, act as an SEI film, reduce the loss of Na ions caused by the rupture and regeneration of the SEI film, improve the initial efficiency of the material, and at the same time can effectively inhibit the formation of sodium dendrites and improve the safety performance of the sodium-ion battery. The nano-thickness of the solid electrolyte film can also improve the utilization rate of the film and reduce costs. Table 1 shows the charge-discharge capacity and the initial efficiency value of the negative electrode material when the negative electrode materials obtained in the examples and comparative examples of the present invention are applied to sodium-ion batteries. It can be seen from Table 1 that under the same test conditions, the modified negative electrode materials prepared in Examples 1 and 2 have higher initial efficiency and charge-discharge capacity.

[0014] The present invention uses high-vacuum magnetron sputtering technology to uniformly and densely coat the solid electrolyte material on the surface of the negative electrode sheet. By controlling the process parameters during the sputtering process, including sputtering power, pressure, temperature, oxygen-argon content ratio, gas flow rate, etc., a solid electrolyte film with a nano-scale thickness is grown on the negative electrode sheet. This film can not only significantly improve the electrochemical performance of the sodium-ion battery, but also inhibit the formation of sodium dendrites and improve the cycle stability and safety of the battery. Description of the Drawings

[0015] Figure 1 is the SEM photo of the negative electrode sheet prepared in Example 1;

[0016] Figure 2 It is the SEM photograph of the negative electrode sheet obtained in Example 1 after 500 battery cycles;

[0017] Figure 3 It is the change of the relative capacity of the negative electrode sheets obtained in Example 1 and Comparative Example 1 with the number of battery cycles. Detailed implementation manners

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0019] The following will describe in detail the specific implementation manners of the present invention with reference to the accompanying drawings. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0020] The first aspect of the present invention provides a negative electrode sheet for a sodium ion battery, wherein the negative electrode sheet for a sodium ion battery includes: hard carbon and a solid electrolyte film coating the hard carbon.

[0021] According to the present invention, coating the solid electrolyte film on the surface of the electrode sheet body is different from coating the active substance particles constituting the electrode in the prior art. The electron insulation of the coating layer of the present invention will not hinder the electron transport inside the electrode, and truly improves the first efficiency of the hard carbon material; the thickness of the coating layer on the surface of the electrode of the present invention is nanoscale, which can reduce the mass transfer resistance during the application of the electrode, improve the utilization rate of the solid electrolyte film, and increase the production cost; the coating layer of the present invention has good compactness, and the composition and thickness are more uniform, which improves the negative electrode conductivity, reduces the contact between the electrolyte and the negative electrode material, has the function of the SEI film, reduces the Na ion loss caused by the rupture and regeneration of the SEI film, improves the first efficiency of the material, and can effectively inhibit the formation of sodium dendrites and improve the safety performance of the sodium ion battery. The treated hard carbon electrode has lower impedance, longer cycle life, higher first efficiency and better safety performance.

[0022] According to the present invention, in order to accurately control the nanoscale thickness, coverage area and coverage position of the solid electrolyte film coating on the electrode surface, preferably, based on the total weight of the negative electrode sheet, the content of the hard carbon is 97-99% by weight, and the content of the solid electrolyte film is 1-3% by weight.

[0023] Further preferably, based on the total weight of the negative electrode sheet, the content of the hard carbon is 98.6-99.1% by weight, and the content of the solid electrolyte membrane is 0.9-1.4% by weight.

[0024] According to the present invention, in order to enable the electrode material to have good fast charge and discharge performance, especially excellent low-temperature charge and discharge performance, preferably, the hard carbon is at least one of resin carbon, organic polymer pyrolysis carbon, carbon black, and biochar, and further preferably resin carbon.

[0025] Preferably, the specific surface area of the hard carbon is 1-2.5 m 2 / g, and the pore volume is 0.05-0.5 cm 3 / g.

[0026] According to the present invention, in order to enable the electrode material to have high thermal stability and chemical / electrochemical stability, preferably, the material constituting the solid electrolyte membrane is doped sodium-based superionic conductor NaSICON, preferably Na 3.3 Zr 1.7 La 0.3 Si 2 PO 12 ,Na 3.3 Zr 1.85 Mg 0.15 Si 2 PO 12 ,Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 etc.

[0027] In the present invention, the hard carbon and the doped sodium-based superionic conductor NaSICON can be commercially available products or prepared by existing methods.

[0028] According to the present invention, in order to reduce the mass transfer resistance during the application of the electrode and improve the utilization rate of the solid electrolyte membrane, preferably, the average thickness of the solid electrolyte membrane is 10-100 nm, and further preferably 10-60 nm.

[0029] According to the present invention, preferably, the hetero-valent cations in the hetero-valent cation-doped sodium-based superionic conductor NaSICON are Mg 2+ 、Ca 2+ 、Sr 2+ 、Ba 2+ 、Zn 2+ 、Co 2+ 、Sc 3+ 、Pr 3+ 、Eu 3+, Lu 3+ , La 3+ , Nb 5+ at least one of

[0030] Further preferably, the heterovalent cation is preferably Zn 2+ , Mg 2+ , La 3+ or Eu 3+ .

[0031] According to the present invention, preferably, relative to 1 mol of the heterovalent cation-doped sodium-based superionic conductor NaSICON, the molar number of the heterovalent cation is 0.0002 - 0.4 mol.

[0032] In the present invention, when the material constituting the solid electrolyte membrane is changed to undoped sodium-based superionic conductor NaSICON, the performance of the negative electrode sheet obtained deteriorates.

[0033] The present invention does not particularly limit the preparation method of the negative electrode sheet of the sodium ion battery, and the preparation method provided in the second aspect of the present invention can also be adopted.

[0034] In the present invention, the structure of the negative electrode sheet of the sodium ion battery is obtained by scanning electron microscopy (SEM) and transmission electron microscopy, and the composition of the negative electrode sheet of the sodium ion battery is obtained by calculating the feeding amount.

[0035] The second aspect of the present invention provides a method for preparing a negative electrode sheet of a sodium ion battery, wherein the method includes:

[0036] (1) Press and mold the solid electrolyte material, and sinter it to obtain a solid electrolyte target;

[0037] (2) Use hard carbon as a substrate, and perform magnetron sputtering to obtain a substrate with a solid electrolyte membrane coated on the surface;

[0038] (3) Heat-treat the substrate with the solid electrolyte membrane coated on the surface to obtain the negative electrode sheet of the sodium ion battery.

[0039] The present invention prepares a ultra-thin solid electrolyte membrane on the electrode surface through magnetron sputtering technology. By controlling magnetron sputtering conditions, including factors such as target-substrate distance, rotation speed, pressure, etc., precise control of the nano-scale thickness, density, coverage area, and coverage position of the solid electrolyte layer on the electrode surface can be achieved, thereby improving the conductivity of the negative electrode and improving the safety of the obtained negative electrode sheet during application. The present invention conducts electrochemical performance tests on the negative electrode sheet prepared by the method. From the test results, it can be seen that the negative electrode sheet coated with the solid electrolyte has lower impedance, longer cycle life, higher initial efficiency, and better safety performance.

[0040] According to the preparation method of the present invention, in order to make the prepared negative electrode material of the electrode have high thermal stability and chemical / electrochemical stability, preferably, the solid electrolyte material is doped sodium-based superionic conductor NaSICON.

[0041] More preferably, the hetero-valent cation is Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ , Co 2+ , Sc 3+ , Pr 3+ , Eu 3+ , Lu 3+ , Nb 5+ or at least one of the following; even more preferably Zn 2+ , Mg 2+ , La 3+ or Eu 3+ .

[0042] According to the preparation method of the present invention, preferably, relative to 1 mol of the hetero-valent cation-doped sodium-based superionic conductor NaSICON, the molar number of the hetero-valent cation is 0.0002 - 0.4 mol.

[0043] According to the preparation method of the present invention, in order to make the target material evenly distributed, preferably, in step (1), the pressure for pressing and forming is 20 - 80 MPa, and more preferably 30 - 60 MPa.

[0044] According to the preparation method of the present invention, in order to sinter and form the solid electrolyte, in step (1), the sintering is carried out under a protective atmosphere, the temperature is 200 - 1000 °C, preferably 400 - 800 °C, and the time is 2 - 6 h, preferably 3 - 5 h.

[0045] Preferably, the protective atmosphere is one or more of nitrogen, helium, neon, and argon.

[0046] According to the preparation method of the present invention, in order to make the prepared electrode material have good fast charge and discharge performance, especially excellent low-temperature charge and discharge performance, preferably, in step (2), the negative electrode sheet is at least one of resin carbon, organic polymer pyrolytic carbon, carbon black, and biochar, and more preferably resin carbon.

[0047] Preferably, the specific surface area of the hard carbon is 1 - 2.5 m 2 / g, and the pore volume is 0.05 - 0.5 cm 3 / g.

[0048] According to the preparation method of the present invention, in order to precisely control the nano-scale thickness, density, coverage area, and coverage position of the solid electrolyte layer on the electrode surface, thereby achieving an increase in the conductivity of the negative electrode and improving the safety of the obtained negative electrode during application, preferably, in step (2), the conditions for magnetron sputtering are as follows: the power is 300 - 700 W, the temperature is 30 - 300 °C, the pressure is 10 -3 -10 -5 Pa, the oxygen-to-argon content ratio is 1:10 - 1:40, the gas flow rate is 20 - 40 sccm, the target-substrate distance is 6 - 8 cm, the rotation speed is 20 - 40 r / min, and the time is 5 - 7 h.

[0049] In the preparation method of the present invention, the thickness of the solid electrolyte film on the surface of the obtained negative electrode sheet is controlled by controlling the time of magnetron sputtering.

[0050] According to the preparation method of the present invention, in order to eliminate internal stress, preferably, in step (3), the heat treatment is annealing.

[0051] Further preferably, the conditions for annealing include: under vacuum conditions, preferably 0.01 - 0.5 MPa, the annealing temperature is 100 - 800 °C, preferably 300 - 600 °C, and the time is 2 - 8 h, preferably 3 - 5 h.

[0052] The third aspect of the present invention provides a negative electrode sheet for a sodium-ion battery prepared by the preparation method provided in the second aspect of the present invention.

[0053] The fourth aspect of the present invention provides a sodium-ion battery, wherein the sodium-ion battery includes a positive electrode, an electrolyte, a separator, and a negative electrode, and the negative electrode includes the negative electrode sheet for a sodium-ion battery of the present invention.

[0054] According to the present invention, the active material of the positive electrode is: (1) P2, O3, P3, or O2 type layered oxides, with the general formula Na x MO 2 , where M is one or more transition metal elements or other doping and substitution elements, such as Al, Mg, etc.; (2) tunnel-type oxides; (3) Prussian blue compounds, with the general formula Na x MM’(CN) 6 ·xH 2 O, usually M’ is Fe element, and M is a transition metal element; (4) sulfates, including phosphates, pyrophosphates, and fluorophosphates, etc., such as Na 3 V 2 (PO 4 ) 3 with a NASICON structure, but not limited to the listed examples; (4) organic compounds.

[0055] According to the present invention, the electrolyte is one of a liquid electrolyte, a solid-liquid composite electrolyte, and a solid electrolyte.

[0056] According to the present invention, the separator is a cellulose fiber composite separator.

[0057] According to the present invention, the positive electrode of the sodium-ion battery, the separator, and the negative electrode of the sodium-ion battery coated with the solid electrolyte are assembled by winding or laminating.

[0058] According to the present invention, the sodium-ion battery can be made into, but not limited to, a square battery, a cylindrical battery, or a soft-pack battery.

[0059] Preferably, the upper cut-off voltage of the sodium-ion battery is 3.8 - 4.2V.

[0060] The present invention will be described in detail below through examples.

[0061] Na 3.3 Zr 1.7 La 0.3 Si 2 PO 12 , with a purity of 99.9%, purchased from Haistars Power Co., Ltd.

[0062] Na 3.3 Zr 1.85 Mg 0.15 Si 2 PO 12 , with a purity of 99.9%, purchased from Haistars Power Co., Ltd.

[0063] Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 , with a purity of 99.9%, purchased from Haistars Power Co., Ltd.

[0064] The structure of the negative electrode sheet of the sodium-ion battery is obtained by scanning electron microscopy (SEM) and transmission electron microscopy tests, and the composition of the negative electrode sheet of the sodium-ion battery is obtained by calculating the feeding amount.

[0065] Example 1

[0066] (1) Take Na 3.3 Zr 1.7 La 0.3 Si 2 PO 12Place it in a copper-back mold, press the solid electrolyte into shape under a pressure of 40 MPa, then place it in a tube furnace, sinter it for 4 h under an argon atmosphere at 800 °C, and cool it naturally to obtain a uniform and dense NASICON-type solid electrolyte target;

[0067] (2) Use the dried resin carbon (specific surface area of 2.0798 m 2 / g) as the substrate, and install it together with the NASICON-type solid electrolyte target obtained in step (1) into a magnetron device; pump the pressure in the chamber to a high vacuum state of 10 -4 Pa, introduce the sputtering gas oxygen-argon mixed gas, control the flow rate at 30 sccm, the target-substrate distance is 7 cm, and the rotation speed is 30 r / min. By adjusting the sputtering process parameters, adjust the sputtering power to 500 W, the working pressure to 10 -4 Pa, the oxygen-argon content ratio to 2:40, and the temperature to 180 °C, and sputter for 6 h to obtain a substrate coated with a solid electrolyte film on the surface;

[0068] (3) Place the substrate coated with a solid electrolyte film on the surface obtained in step (1) in a high-temperature oven, evacuate to 0.1 MPa, carry out high-temperature holding at 400 °C for 4 h, and naturally cool and anneal to obtain the negative electrode sheet 1 of the sodium-ion battery.

[0069] Observe the negative electrode sheet 1 of the sodium-ion battery by scanning electron microscope (SEM), and the scanning results are as Figure 1 shown. It can be seen from Figure 1 that the surface of the negative electrode 1 of the sodium-ion battery obtained in Example 1 is smooth and dense, and the thickness is uniform; apply the negative electrode sheet 1 of the sodium-ion battery to the sodium-ion battery. After the battery is cycled 500 times, scan the disassembled negative electrode sheet 1 by scanning electron microscope (SEM), and the results are as Figure 2 shown. It can be seen from Figure 2 that after being cycled 500 times in the battery, the surface of the negative electrode sheet 1 is still smooth and dense, the thickness is uniform, and no crystal branches are generated on the surface of the negative electrode sheet 1.

[0070] Perform transmission electron microscopy measurement on the negative electrode sheet 1 of the sodium-ion battery. From the measurement results, it can be known that the average thickness of the solid electrolyte film coated on the surface of the negative electrode 1 of the sodium-ion battery is 30 nm; weigh the resin carbon before and after sputtering. After calculation, based on the total weight of the negative electrode sheet 1 of the sodium-ion battery, the resin carbon content in the negative electrode sheet 1 of the sodium-ion battery is 99 wt%, and the content of the solid electrolyte film is 1 wt%.

[0071] Example 2

[0072] According to the method of Example 1, the difference is that the sputtering time is extended to 8 h to obtain the negative electrode sheet 2 of the sodium-ion battery.

[0073] In the same manner as in Example 1, the negative electrode sheet 2 of the sodium-ion battery was scanned by SEM. From the scanning results, it can be seen that after 500 cycles in the battery, the surface of the negative electrode sheet 2 is still smooth and dense, with uniform thickness, and no dendritic crystals are formed on the surface of the negative electrode sheet.

[0074] The negative electrode sheet 2 of the sodium-ion battery was measured by transmission electron microscopy. From the measurement results, it can be known that the average thickness of the solid electrolyte film coated on the surface of the negative electrode sheet 2 of the sodium-ion battery is 40 nm; the resin carbon before and after sputtering was weighed, and through calculation, based on the total weight of the negative electrode sheet 2 of the sodium-ion battery, the resin carbon content in the negative electrode sheet 1 of the sodium-ion battery is 98.6 wt%, and the content of the solid electrolyte film is 1.4 wt%.

[0075] Example 3

[0076] According to the method of Example 1, except that Na 3.3 Zr 1.7 La 0.3 Si 2 PO 12 was changed to Na 3.3 Zr 1.85 Mg 0.15 Si 2 PO 1 , the negative electrode sheet 3 of the sodium-ion battery was obtained.

[0077] In the same manner as in Example 1, the negative electrode sheet 3 of the sodium-ion battery was scanned by SEM. From the scanning results, it can be seen that after 500 cycles in the battery, the surface of the negative electrode sheet 3 is still smooth and dense, with uniform thickness, and no dendritic crystals are formed on the surface of the negative electrode sheet.

[0078] The negative electrode sheet 3 of the sodium-ion battery was measured by transmission electron microscopy. From the measurement results, it can be known that the average thickness of the solid electrolyte film coated on the surface of the negative electrode 3 of the sodium-ion battery is 28 nm; the resin carbon before and after sputtering was weighed, and through calculation, based on the total weight of the negative electrode sheet 3 of the sodium-ion battery, the resin carbon content in the negative electrode sheet 3 of the sodium-ion battery is 99.1 wt%, and the content of the solid electrolyte film is 0.9 wt%.

[0079] Example 4

[0080] According to the method of Example 1, except that Na 3.3 Zr 1.7 La 0.3 Si 2 PO 12 was changed to Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O12 , the negative electrode sheet 4 of the sodium-ion battery is obtained.

[0081] In the same manner as in Example 1, SEM scanning was performed on the negative electrode sheet 4 of the sodium-ion battery. From the scanning results, it can be seen that after 500 cycles in the battery, the surface of the negative electrode sheet 4 is still smooth and dense, with uniform thickness, and no crystal branches are generated on the surface of the negative electrode sheet.

[0082] Transmission electron microscopy measurement was performed on the negative electrode sheet 4 of the sodium-ion battery. From the measurement results, it can be known that the average thickness of the solid electrolyte film coated on the surface of the negative electrode 4 of the sodium-ion battery is 32 nm; the resin carbon negative electrode sheet before and after sputtering was weighed, and after calculation, based on the total weight of the negative electrode sheet 4 of the sodium-ion battery, the resin carbon content in the negative electrode sheet 4 of the sodium-ion battery is 98.8% by weight, and the content of the solid electrolyte film is 1.2% by weight.

[0083] Comparative Example 1

[0084] Uncoated resin carbon, specific surface area 2.0798 m 2 / g.

[0085] Comparative Example 2

[0086] Uncoated biochar, specific surface area is 3.4324 m 2 / g.

[0087] Comparative Example 3

[0088] Uncoated organic polymer pyrolytic carbon, specific surface area is 2.8032 m 2 / g.

[0089] Test Example

[0090] The negative electrodes of the sodium-ion batteries respectively contain the negative electrode sheets of the sodium-ion batteries prepared in the examples and comparative examples. Specifically, the negative electrodes of the sodium-ion batteries include (by weight): 95% by weight of the negative electrode sheet of the sodium-ion battery, 1% by weight of conductive carbon black, 1% by weight of binder, and 3% by weight of CMC.

[0091] The positive electrodes of the sodium-ion batteries include (by weight): 94.7% by weight of layered oxide material, 2.5% by weight of binder, 2% by weight of conductive carbon black, and 0.8% of conductive agent.

[0092] The separator of the sodium-ion battery is a cellulose fiber composite material.

[0093] Preparation of the sodium-ion battery: Conductive electrode ears were respectively welded on the positive electrode sheet and the negative electrode sheet, the separator was placed between the positive electrode and the negative electrode, and it was wound to form a bare battery core, which was wrapped in an aluminum-plastic film; the electrolyte was injected; it was encapsulated, and the battery was formed and aged to obtain a plurality of soft-packaged batteries.

[0094] Electrochemical performance tests were carried out on the obtained multiple soft-packaged batteries. The test conditions were: constant current and constant voltage charging at 0.2C / 0.2C at room temperature, and constant current and constant voltage discharging. The test results are shown in Table 1:

[0095] Table 1

[0096]

[0097]

[0098] As can be seen from Table 1, the initial efficiency of the sodium-ion battery using the coated negative electrode sheet is significantly higher than that of the sodium-ion battery using the uncoated negative electrode sheet; the charge and discharge capacities of the sodium-ion battery using the coated negative electrode sheet are significantly greater than those of the sodium-ion battery using the uncoated negative electrode sheet.

[0099] From the above examples and comparative examples, it can be seen that when the hard carbon negative electrode coated with the solid electrolyte of the present invention is applied to a sodium-ion battery, it is found that the modified negative electrode material has higher initial efficiency and charge-discharge capacity, and during use, the solid electrolyte coating film can also inhibit the formation of sodium dendrites on the electrode surface, improving the cycle stability and safety of the battery.

[0100] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A negative electrode sheet for a sodium-ion battery, characterized in that, the negative electrode sheet for a sodium-ion battery comprises: hard carbon and a solid electrolyte film coating the hard carbon.

2. The negative electrode sheet for a sodium-ion battery according to claim 1, wherein, based on the total weight of the negative electrode sheet for a sodium-ion battery, the content of the hard carbon is 97-99% by weight, and the content of the solid electrolyte film is 1-3% by weight; preferably, the content of the hard carbon is 98.6-99.1% by weight, and the content of the solid electrolyte film is 0.9-1.4% by weight.

3. The negative electrode sheet according to claim 1 or 2, wherein, the hard carbon is at least one of resin carbon, organic polymer pyrolysis carbon, carbon black, and biochar; and / or, the specific surface area of the hard carbon is 1-2.5 m 2 / g, and the pore volume is 0.05-0.5 cm 3 / g.

4. The negative electrode sheet according to any one of claims 1-3, wherein, the material constituting the solid electrolyte film is a heterovalent cation-doped sodium-based superionic conductor NaSICON; and / or, the average thickness of the solid electrolyte film is 10-100 nm, preferably 10-60 nm.

5. The negative electrode sheet according to claim 4, wherein, The hetero-valent cation in the hetero-valent cation-doped sodium-based superionic conductor NaSICON is Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ , Co 2+ , Sc 3+ , Pr 3+ , Eu 3+ , Lu 3+ , La 3+ , Nb 5+ or at least one of them; Preferably, the hetero-valent cation is preferably Zn 2+ , Mg 2+ , La 3+ or Eu 3+ ; and / or, relative to 1 mol of the heterovalent cation-doped sodium-based superionic conductor NaSICON, the number of moles of the heterovalent cation is 0.0002-0.4 mol.

6. A method for preparing a negative electrode sheet for a sodium-ion battery, characterized in that, the method comprises: (1) Compacting and sintering a solid electrolyte material to obtain a solid electrolyte target; (2) Using hard carbon as a substrate and performing magnetron sputtering to obtain a substrate with a solid electrolyte film coated on the surface; (3) Heat-treating the substrate with the solid electrolyte film coated on the surface to obtain the negative electrode sheet for a sodium-ion battery.

7. The preparation method according to claim 6, wherein, in step (1), the pressure for compacting is 20-80 MPa, preferably 30-60 MPa; and / or, the sintering is carried out in a protective atmosphere at a temperature of 200-1000 °C, preferably 400-800 °C, and the time is 2-6 h, preferably 3-5 h.

8. The preparation method according to claim 6 or 7, wherein, in step (1), the solid electrolyte material is a heterovalent cation-doped sodium-based superionic conductor NaSICON; Among them, the hetero-valent cation is Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Zn 2+ , Co 2+ , Sc 3+ , Pr 3+ , Eu 3+ , La 3+ , Lu 3+ , Nb 5+ and at least one of them; Preferably, the hetero-valent cation is preferably Zn 2+ , Mg 2+ , La 3+ or Eu 3+ ; and / or, relative to 1 mol of the heterovalent cation-doped sodium-based superionic conductor NaSICON, the number of moles of the heterovalent cation is 0.0002-0.4 mol.

9. The preparation method according to any one of claims 6-8, wherein, in step (2), the hard carbon is at least one of resin carbon, organic polymer pyrolysis carbon, carbon black, and biochar; and / or, the specific surface area of the hard carbon is 1-2.5 m 2 / g, and the pore volume is 0.05-0.5 cm 3 / g.

10. The preparation method according to any one of claims 6-9, wherein, In step (2), the conditions for magnetron sputtering are as follows: the power is 300 - 700 W, the temperature is 30 - 300 °C, the pressure is 10 -3 - 10 -5 Pa, the oxygen-argon content ratio is 1:10 - 1:40, the gas flow rate is 20 - 40 sccm, the target-substrate distance is 6 - 8 cm, the rotation speed is 20 - 40 r / min, and the time is 5 - 7 h.

11. The preparation method according to any one of claims 6-10, wherein, in step (3), the heat treatment is annealing; Preferably, the conditions for annealing include: under a vacuum condition, preferably 0.01 - 0.5 MPa, the annealing temperature is 100 - 800 °C, preferably 300 - 600 °C, and the time is 2 - 8 h, preferably 3 - 5 h.

12. A negative electrode sheet for a sodium ion battery prepared by the preparation method according to any one of claims 6 - 11.

13. A sodium ion battery, characterized in that the sodium ion battery includes a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the negative electrode comprises the negative electrode sheet for a sodium ion battery according to any one of claims 1 - 5 and 12.

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