Electrode negative for sodium ion battery, preparation method thereof and sodium ion battery

Abstract

This invention relates to the field of battery technology, and in particular to a negative electrode for sodium-ion batteries, its preparation method, and a sodium-ion battery. The negative electrode for sodium-ion batteries comprises a hard carbon substrate with a sodium alloy layer modified on its surface; the sodium alloy layer comprises Na… x M; Na x M includes Na x Sn, Na x Bi, Na x Sb, Na x In, Na x Pb, Na x Zn, Na x One or more of Al. The hard carbon substrate with a surface modified with a sodium alloy layer prepared by the present invention uses one or more metals selected from tin, bismuth, antimony, indium, lead, zinc, and aluminum to form an ultra-thin uniform sodium alloy layer in situ, which does not block the hard carbon channels; it can significantly improve electronic conductivity and sodium ion diffusion kinetics.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode for sodium-ion batteries, a method for preparing the same, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have broad application prospects in energy storage and power fields due to their abundant resources and low cost. Hard carbon is the mainstream anode material, but its capacity and rate performance are limited. Metals such as tin, bismuth, antimony, indium, and lead can form high-capacity alloys with sodium, but traditional composite methods involve introducing metal precursors into the electrode and then treating them at high temperatures, which has problems such as complex processes, metal agglomeration, large volume expansion, and poor cycle performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a negative electrode for sodium-ion batteries, a method for preparing the same, and a sodium-ion battery.

[0004] To achieve the above objectives, this application adopts the following solution: A negative electrode for a sodium-ion battery includes a hard carbon substrate with a sodium alloy layer on its surface; the sodium alloy layer comprises Na x M; Na x M includes Na x Sn, Na x Bi, Na x Sb, Na x In, Na x Pb, Na x Zn, Na x One or more of Al, where x is a positive stoichiometric coefficient that satisfies the alloy valence ratio.

[0005] The sodium alloy layer includes Na x Sn, Na x Bi, Na x One or a mixture of Sb; preferably, the molar ratio of metal M in the mixed sodium alloy layer is 1.

[0006] The thickness of the sodium alloy layer is 5 nm to 2 μm; the hard carbon matrix does not contain metal M or its compounds; preferably, the hard carbon matrix has a hierarchical porous structure.

[0007] The present invention also includes a method for preparing the negative electrode of the sodium-ion battery, comprising the following steps: (1) preparing a negative electrode sheet composed of a hard carbon matrix, a conductive agent and a binder, wherein the negative electrode sheet does not contain a metal M source; (2) preparing an electrolyte, wherein a metal M source additive is added to the electrolyte; (3) assembling the negative electrode sheet and the electrolyte into a battery; wherein the battery includes a half-cell or a full-cell; (4) performing a formation treatment on the battery.

[0008] When the battery is a half-cell, the formation potential range is controlled between 0 and 0.8 V vs Na. + / Na; When the battery is a full cell, the cutoff potential is determined according to the positive electrode material used. The formation potential range of the full cell is the cutoff potential minus 0.8 V to the cutoff potential. Within the corresponding formation potential range, the metal M source additive in the electrolyte is reduced and forms a sodium alloy with sodium in situ, and a sodium alloy layer is generated on the hard carbon surface.

[0009] The formation process in step (4) is as follows: when the battery is a half-cell, discharge it to 0V~0.8V with a small current of 0.01C~0.2C, preferably to 0.4V with 0.1C, maintain constant voltage for 0.5h~4h, preferably maintain constant voltage for 1h, and then continue to discharge until cutoff to complete in-situ alloying; When the battery is a full cell, it is charged with a small current of 0.01 C to 0.2 C to the cutoff potential minus 0.8 V to the cutoff voltage, preferably 0.1 C to the cutoff potential minus 0.4 V, and held at a constant voltage for 0.5 h to 4 h, preferably 1 h, and then charged to the cutoff potential to complete the in-situ alloying.

[0010] The mass ratio of hard carbon, conductive agent, and binder in the negative electrode sheet is (80~98):(1~10):(1~10); preferably 90:5:5; preferably, the conductive agent is at least one of conductive carbon black, carbon nanotubes, carbon fiber, and graphene; the binder is at least one of CMC, SBR, polyacrylic acid, and PVDF.

[0011] The electrolyte includes sodium salt, solvent, and additives; the additives include metal M-source additives and film-forming additives. Preferably, the amount of the metal M source additive added to the electrolyte is 0.05 wt% to 10 wt%; more preferably 0.2 wt% to 5 wt%; more preferably 0.08 wt%; the metal M is selected from one or more of tin, bismuth, antimony, indium, lead, zinc, and aluminum; preferably, the metal M source additive includes one or more of inorganic metal salts, organometallic compounds, and metal coordination compounds. Preferably, the solvent includes one or a mixture of EC and DEC; more preferably, it is a mixture of EC and DEC in a mass ratio of 1:1. Preferably, the film-forming additive includes one or a mixture of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and propylene sulfonate lactone (PS).

[0012] The full cell further includes a positive electrode and a separator; the positive electrode includes at least one of polyanionic positive electrode material, layered oxide positive electrode material, and Prussian blue positive electrode material; the separator is one of polypropylene separator, polyethylene separator, glass fiber separator, and cellulose composite separator; the counter electrode of the half cell is a sodium sheet.

[0013] The present invention also includes a sodium-ion battery, comprising the negative electrode for the sodium-ion battery.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The hard carbon substrate prepared by this invention, with a surface-modified sodium alloy layer, utilizes one or more metals selected from tin, bismuth, antimony, indium, lead, zinc, and aluminum to form an ultra-thin, uniform sodium alloy layer in situ, without clogging the hard carbon channels. This significantly improves electronic conductivity and sodium ion diffusion kinetics, achieving a 5C capacity retention rate of ≥75% and a reversible capacity of 350~450 mAh / g. The alloy layer structure is stable, with controllable volume expansion, and a capacity retention rate of ≥85% after 500 cycles. The initial coulombic efficiency is 3%~10% higher than that of pure hard carbon. The alloy layer can be used in single-metal or multi-metal blends, offering flexible formulations and wide applicability. Furthermore, the preparation process is extremely simple, requiring no high-temperature sintering, metal coating, or precursor blending, and is directly compatible with existing hard carbon anode production lines. Attached Figure Description

[0015] Figure 1 This is an HRTEM image of a hard carbon substrate SEI with a sodium alloy layer on its surface, according to an embodiment of the present invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0017] Example 1: Na with a surface modified with a sodium alloy layer x M-hard carbon matrix, with metal M-source additive at standard concentration, stannous trifluoromethanesulfonate, prepared as follows: Anode: 90% hard carbon matrix + 5% conductive carbon black + 5% polyacrylic acid; Electrolyte: EC:DEC = 1:1, 1 M NaPF6, with the addition of 0.8 wt% stannous trifluoromethanesulfonate + 2 wt% FEC; The full cell also includes the positive electrode: 94% sodium iron pyrophosphate (NFPP) + 3% conductive carbon black + 3% PVDF; Diaphragm: Glass fiber; The counter electrode of the half-cell is a sodium plate.

[0018] Formation: For half-cell, discharge at 0.1C to 0.2V, maintain constant voltage for 1 hour, and then continue discharging to 0.005V (cutoff); For full-cell, charge at 0.1C to 3.3V, maintain constant voltage for 1 hour, and then continue charging to 3.5V (cutoff). In-situ product: Na x The Sn alloy layer is approximately 80 nm thick.

[0019] Example 2: The difference between Example 2 and Example 1 is that the concentration of single tin-based electrolyte is low; electrolyte: EC:DEC=1:1, 1 M NaPF6, with the addition of 0.2 wt% stannous trifluoromethanesulfonate + 2 wt% FEC; Example 3: The difference between Example 3 and Example 1 is that the single tin-based electrolyte has a high concentration; the electrolyte is: EC:DEC=1:1, 1 M NaPF6, with the addition of 5.0 wt% stannous trifluoromethanesulfonate + 2 wt% FEC; Example 4: The difference between Example 4 and Example 1 is that the single tin base in the electrolyte is a different tin salt: stannous chloride; the electrolyte is: EC:DEC=1:1, 1 M NaPF6, with the addition of 0.8 wt% stannous chloride SnCl2 + 2 wt% FEC; Example 5: The difference between Example 5 and Example 1 is that the metal M source additive is a single metal bismuth-based electrolyte; the electrolyte is EC:DEC=1:1, 1 M NaPF6, with the addition of 0.8 wt% bismuth trifluoromethanesulfonate + 2 wt% FEC. Formation: Half-cell, discharge at 0.1C to 0.4V, maintain constant voltage for 1 hour, then continue discharging to 0.005V (cutoff); Full-cell, charge at 0.1C to 3.1V, maintain constant voltage for 1 hour, then continue charging to 3.5V (cutoff). In-situ product: Na x Bi alloy layer.

[0020] Example 6: The difference between Example 6 and Example 1 is that the metal M source additive is a single metal antimony-based electrolyte; the electrolyte is EC:DEC=1:1, 1 M NaPF6, with the addition of 0.8 wt% antimony trichloride SbCl3 + 2 wt% FEC. Formation: For half-cell, discharge at 0.1C to 0.4V, maintain constant voltage for 1 hour, and then continue discharging to 0.005V to cut off; for full-cell, charge at 0.1C to 3.1V, maintain constant voltage for 1 hour, and then continue charging to 3.5V to cut off.

[0021] In-situ product: Na x Sb alloy layer.

[0022] Example 7: The difference between Example 7 and Example 1 is that the metal M source additive is a single metal indium-based; the electrolyte is EC:DEC = 1:1, 1 M NaPF6, with the addition of 0.8 wt% indium trichloride InCl3 + 2 wt% FEC; the in-situ product is Na... x In alloy layer.

[0023] Example 8: The difference between Example 8 and Example 1 is that the metal M source additive is a single metal lead-based additive; the electrolyte is EC:DEC = 1:1, 1 M NaPF6, with the addition of 0.8 wt% lead trifluoromethanesulfonate + 2 wt% FEC; the in-situ product is Na… x Pb alloy layer.

[0024] Example 9: The difference between Example 9 and Example 1 is that the metal M source additive is a single metal zinc-based electrolyte; the electrolyte is EC:DEC=1:1, 1 M NaPF6, with the addition of 0.8 wt% zinc acetate Zn(Ac)2 + 2 wt% FEC. Formation: For half-cells, discharge at 0.1C to 0.5V, maintain constant voltage for 1 hour, and then continue discharging to 0.005V (cutoff); for full-cells, charge at 0.1C to 3.0V, maintain constant voltage for 1 hour, and then continue charging to 3.5V (cutoff). In-situ product: Na x Zn alloy layer.

[0025] Example 10: The difference between Example 10 and Example 1 is that the metal M source additive is a single-metal aluminum-based electrolyte; the electrolyte is EC:DEC = 1:1, 1 M NaPF6, with the addition of 0.8 wt% aluminum trifluoromethanesulfonate + 2 wt% FEC; the in-situ product is Na… x Al alloy layer.

[0026] Example 11: The difference between Example 11 and Example 1 is that the metal M source additive is a bimetal; the bimetal molar ratio is 1:1; tin + bismuth; electrolyte: EC:DEC=1:1, 1 M NaPF6, 0.4 wt% stannous trifluoromethanesulfonate + 0.4 wt% bismuth trifluoromethanesulfonate + 2 wt% FEC; Formation: For half-cells, discharge at 0.1C to 0.4V, maintain constant voltage for 0.5h, then discharge to 0.2V, maintain constant voltage for 0.5h, and continue discharging to 0.005V (cutoff); For full-cells, charge at 0.1C to 3.1V, maintain constant voltage for 0.5h, then charge to 3.3V, maintain constant voltage for 0.5h, and continue charging to 3.5V (cutoff). In-situ product: Na x Sn+Na x Bi dual-phase alloys.

[0027] Example 12: The difference between Example 12 and Example 1 is that the metal M source additive is a bimetal: the bimetal molar ratio is 1:1; tin + zinc; the electrolyte: EC:DEC=1:1, 1 M NaPF6, 0.4 wt% stannous trifluoromethanesulfonate + 0.4 wt% zinc acetate + 2 wt% FEC; Formation: For half-cells, discharge at 0.1C to 0.5V, maintain constant voltage for 0.5h, then discharge to 0.2V, maintain constant voltage for 0.5h, and continue discharging to 0.005V (cutoff); For full-cells, charge at 0.1C to 3.0V, maintain constant voltage for 0.5h, then charge to 3.3V, maintain constant voltage for 0.5h, and continue charging to 3.5V (cutoff). In-situ product: Na x Sn+Na x Zn dual-phase alloys

[0028] Example 13: The difference between Example 13 and Example 1 is that the metal M source additive is a trimetallic compound: tin + antimony + bismuth; the molar ratio of the three metals is 1:1:1; the electrolyte is: EC:DEC=1:1, 1 M NaPF6, 0.4 wt% stannous trifluoromethanesulfonate + 0.2 wt% antimony trichloride + 0.2 wt% bismuth trifluoromethanesulfonate + 2 wt% FEC; Formation: For half-cells, discharge at 0.1C to 0.4V, maintain constant voltage for 0.5h, then discharge to 0.2V, maintain constant voltage for 0.5h, and continue discharging to 0.005V (cutoff); For full-cells, charge at 0.1C to 3.1V, maintain constant voltage for 0.5h, then charge to 3.3V, maintain constant voltage for 0.5h, and continue charging to 3.5V (cutoff). In-situ product: Na x Sn+Na x Sb+Na x Bi three-phase alloy.

[0029] Comparative Example 1: Pure hard carbon anode (without metal additives). The difference from Example 1 is that the anode is composed of 90% hard carbon, 5% conductive agent, and 5% binder; the electrolyte is composed of EC:DEC = 1:1, 1 M NaPF6, and 2 wt% FEC; and it has no sodium alloy layer.

[0030] Comparative Example 2: Traditional electrode premixed tin (non-in-situ), the difference from Example 1 is that the negative electrode is composed of 85% hard carbon, 5% tin powder, 5% conductive agent, and 5% binder; the electrolyte is free of metal additives.

[0031] Comparative Example 3: Formation without constant voltage stage. The difference from Example 1 is that the formation process is as follows: half-cell, continuously discharged at 0.1C to 0.005 V, without constant voltage maintenance; full-cell, continuously charged at 0.1C to 3.5 V, without constant voltage maintenance.

[0032] Comparative Example 4: High-potential formation, the difference from Example 1 is that the formation process is as follows: half-cell, discharged at 0.1C to 1V, held at constant voltage for 1 h, and then discharged at 0.1C to 0.005V to cut off; full-cell, charged at 0.1C to 2.5V, held at constant voltage for 1 h, and then charged at 0.1C to 3.5V to cut off.

[0033] Electrochemical performance testing methods The negative electrode sheets prepared in each embodiment and comparative example were assembled into coin cell half-cells, with a sodium metal sheet as the counter electrode. The capacity and initial coulombic efficiency were tested in a battery testing system. Voltage window: 0.005 V~2.0 V (vs Na) + / Na) Initial coulombic efficiency: 0.1C first-cycle discharge capacity / charge capacity The negative and positive electrode sheets prepared in each embodiment and comparative example were assembled into coin cell full cells, and the rate capability and cycle stability were tested in a battery testing system. Voltage window: 1.5 V~3.5 V (vs Na) + / Na) Rate performance: 0.1C, 0.5C, 1C, 2C, 5C constant current charge and discharge. 5C capacity retention rate = 5C capacity / 0.5C capacity × 100% Cyclic stability: Calculate capacity retention after 500 cycles at 0.5C. Table 1 shows the test results of sodium alloy hard carbon anode batteries.

[0034] Table 1

[0035] The results showed that for single-metal systems, Sn and Sb exhibited the best performance, with a capacity >420 mAh / g and a 5C retention rate >75%. Bi, In, Pb, Zn, and Al showed good improvement in that order. Regarding metal salts, trifluoromethanesulfonate, chloride, and acetate could all be in-situ alloyed with similar performance. Concentration optimization was achieved in the range of 0.2–1.0 wt%, with insufficient alloying at lower concentrations and increased impedance at higher concentrations. For multi-metal complexes, the Sn+Sb+Bi trimetallic combination showed the best performance, with a capacity of 448 mAh / g, a first-cycle efficiency of 90.5%, and a cycle retention rate of 88.5%. The key to formation was the presence of Na at 0–0.8 V. + / Na low potential constant voltage is required to form a uniform and continuous sodium alloy layer; the in-situ alloying of the electrolyte in this invention is significantly better than the traditional electrode premixed metal, and comprehensively surpasses the existing technology in terms of capacity, rate capability, cycle life and first efficiency.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0037] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A negative electrode for a sodium-ion battery, characterized in that, Includes a hard carbon substrate with a surface-modified sodium alloy layer; the sodium alloy layer includes Na. x M; Na x M includes Na x Sn, Na x Bi, Na x Sb, Na x In, Na x Pb, Na x Zn, Na x One or more of Al, where x is a positive stoichiometric coefficient that satisfies the alloy valence ratio.

2. The negative electrode for a sodium-ion battery according to claim 1, characterized in that, The sodium alloy layer includes Na x Sn, Na x Bi, Na x One or a mixture of Sb; preferably, the molar ratio of metal M in the mixed sodium alloy layer is 1.

3. The negative electrode for a sodium-ion battery according to claim 1, characterized in that, The thickness of the sodium alloy layer is 5 nm to 2 μm; the hard carbon matrix does not contain metal M or its compounds; preferably, the hard carbon matrix has a hierarchical porous structure.

4. A method for preparing a negative electrode for a sodium-ion battery according to any one of claims 1-3, characterized in that, The process includes the following steps: (1) preparing a negative electrode sheet composed of a hard carbon matrix, a conductive agent, and a binder, wherein the negative electrode sheet does not contain a metal M source; (2) preparing an electrolyte solution, wherein a metal M source additive is added to the electrolyte solution; (3) assembling the negative electrode sheet and the electrolyte solution into a battery; wherein the battery includes a half-cell or a full-cell; and (4) performing a formation treatment on the battery.

5. The preparation method according to claim 4, characterized in that, When the battery is a half-cell, the formation potential range is controlled between 0 and 0.8 V vs Na. + / Na; When the battery is a full cell, the cutoff potential is determined according to the positive electrode material used. The formation potential range of the full cell is the cutoff potential minus 0.8 V to the cutoff potential. Within the corresponding formation potential range, the metal M source additive in the electrolyte is reduced and forms a sodium alloy with sodium in situ, generating a sodium alloy layer on the hard carbon surface.

6. The method for preparing the negative electrode for a sodium-ion battery according to claim 4, characterized in that, The formation process in step (4) is as follows: when the battery is a half-cell, discharge it to 0 V to 0.8 V with a small current of 0.01 C to 0.2 C, preferably to 0.4 V with 0.1 C, maintain constant voltage for 0.5 h to 4 h, preferably maintain constant voltage for 1 h, and then continue to discharge until cutoff to complete in-situ alloying; When the battery is a full cell, it is charged with a small current of 0.01 C to 0.2 C to the cutoff potential minus 0.8 V to the cutoff voltage, preferably 0.1 C to the cutoff potential minus 0.4 V, and held at a constant voltage for 0.5 h to 4 h, preferably 1 h, and then charged to the cutoff potential to complete the in-situ alloying.

7. The method for preparing the negative electrode for a sodium-ion battery according to claim 4, characterized in that, The mass ratio of hard carbon, conductive agent, and binder in the negative electrode sheet is (80~98):(1~10):(1~10); preferably 90:5:5; preferably, the conductive agent is at least one of conductive carbon black, carbon nanotubes, carbon fiber, and graphene; the binder is at least one of CMC, SBR, polyacrylic acid, and PVDF.

8. The method for preparing the negative electrode for a sodium-ion battery according to claim 4, characterized in that, The electrolyte includes sodium salt, solvent, and additives; the additives include metal M-source additives and film-forming additives. Preferably, the amount of the metal M source additive added to the electrolyte is 0.05 wt% to 10 wt%; more preferably 0.2 wt% to 5 wt%; more preferably 0.08 wt%; the metal M is selected from one or more of tin, bismuth, antimony, indium, lead, zinc, and aluminum; preferably, the metal M source additive includes one or more of inorganic metal salts, organometallic compounds, and metal coordination compounds. Preferably, the solvent includes one or a mixture of EC and DEC; more preferably, it is a mixture of EC and DEC in a mass ratio of 1:

1. Preferably, the film-forming additive includes one or a mixture of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and propylene sulfonate lactone (PS).

9. The method for preparing the negative electrode for a sodium-ion battery according to claim 4, characterized in that, The full cell further includes a positive electrode and a separator; the positive electrode includes at least one of polyanionic positive electrode material, layered oxide positive electrode material, and Prussian blue positive electrode material; the separator is one of polypropylene separator, polyethylene separator, glass fiber separator, and cellulose composite separator; the counter electrode of the half cell is a sodium sheet.

10. A sodium-ion battery, characterized in that, Includes the negative electrode for sodium-ion batteries as described in any one of claims 1-3.

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