Modified negative electrode current collector, preparation method and application thereof, and negative-electrode-free sodium metal battery

Abstract

The invention belongs to the field of negative-electrode-free batteries, and particularly discloses a modified negative electrode current collector, a preparation method and application thereof and a negative-electrode-free sodium metal battery, the modified negative electrode current collector comprises a conductive substrate and a modified coating compounded on the surface of the conductive substrate, and the modified coating comprises modified graphite; the modified graphite is obtained by performing first-stage liquid phase modification on graphite through a modifier A and then performing second-stage liquid phase modification treatment on the graphite through a modifier B; the modifier A comprises HF and MFn; m comprises at least one of Cu, Ag, Mg and Ca, and n is the valence of M; the modifier B comprises a compound with a structure shown in a formula 1 (). The modified current collector provided by the invention can effectively reduce irreversible loss of sodium metal in the cycle process of the negative-electrode-free sodium metal battery and guide uniform sodium metal deposition / stripping, so that the long cycle life and the high-temperature performance of the negative-electrode-free sodium metal battery are remarkably improved.

Description

Modified negative electrode current collector, its preparation method, application and sodium metal battery without negative electrode Technical Field

[0001] This invention belongs to the field of sodium metal battery technology, and particularly relates to a modified current collector for a negative electrode in a negative electrode-free sodium metal battery. Background Technology

[0002] Sodium metal secondary batteries without a negative electrode differ fundamentally from traditional batteries containing negative electrode active materials in structure: their negative electrode side does not have any active material that can embed sodium metal, only retaining current collectors or surface-modified current collectors. While this structure helps to improve the battery's operating voltage and energy density, it also makes sodium dendrites easier to form and grow, causing long-cycle performance to often fail to meet the requirements of practical applications.

[0003] To address these challenges, current technological research and development primarily focuses on the interface control and structural modification of current collectors. For example, Chinese patent document CN119213584A discloses a method for constructing a composite undercoat containing at least two of zero-dimensional, one-dimensional, and two-dimensional carbon materials on the surface of a current collector. Chinese patent document CN119213595A discloses a current collector structure with a specific interface protective layer. Chinese patent document CN118398827A discloses a scheme to enhance interface stability by coating a carbon-based functional coating with multi-level particle size and composition design on the substrate surface. Chinese patent document CN118919734A proposes a scheme for a negative electrode current collector using a composite coating of graphite, carbon nanotubes, and a binder.

[0004] Although the aforementioned methods attempt to optimize the current collector interface behavior from different perspectives and improve electrode-electrolyte compatibility to some extent, they still cannot fundamentally suppress sodium dendrite formation or significantly improve the long-cycle stability of the battery under high-current conditions. Furthermore, these methods still cannot effectively address the poor electrochemical performance of anode-less sodium metal batteries at high temperatures, which is a significant obstacle to their commercialization. Therefore, developing novel current collector or electrolyte systems that combine high ion conduction capability, excellent interface stability, and dendrite suppression remains a key issue that urgently needs to be addressed in this field. Summary of the Invention

[0005] To address the problems of severe interfacial side reactions, unstable SEI film, uneven sodium deposition / stripping, and poor high-temperature performance in sodium-metal battery systems without a negative electrode, the primary objective of this invention is to provide a modified negative electrode current collector that is adapted to the characteristics of sodium-metal batteries without a negative electrode and can improve the performance of sodium-metal batteries without a negative electrode, especially their high-temperature performance.

[0006] The second objective of this invention is to provide a method for preparing a modified negative electrode current collector and its application in a sodium metal battery without a negative electrode.

[0007] A third objective of the present invention is to provide a sodium metal battery without a negative electrode, comprising the modified negative electrode current collector described above.

[0008] Existing research on current collector modification in anode-less sodium metal batteries mainly focuses on constructing alloyed sodium-loving coatings to improve the reversibility of sodium deposition / stripping. However, this method is not only costly and unsuitable for commercialization, but also causes significant volume expansion during cycling, leading to coating peeling. Therefore, this invention proposes the following improvement:

[0009] A modified negative electrode current collector includes a conductive substrate and a modified coating composited thereon on its surface, said modified coating including modified graphite.

[0010] The modified graphite is obtained by first-stage liquid-phase modification of graphite with modifier A, followed by second-stage liquid-phase modification with modifier B.

[0011] The modifier A includes HF and MF. n M includes at least one of Cu, Ag, Mg, and Ca, where n is the valence of M.

[0012] The modifier B includes compounds with the structure of Formula 1;

[0013] Formula 1

[0014] In Formula 1, R1 is a C1-C4 alkyl or phenyl group; R2 is an active group or a substituent with an active group; the active group is a hydroxyl, amino, or carboxyl group; a substituent with an active group refers to a substituent with the active group on a C1-C6 alkyl chain, benzene ring, or olefin chain.

[0015] This invention innovatively composites modified graphite containing the aforementioned two stages of liquid-phase modification onto a conductive substrate. Based on the two-stage modification treatment using pretreatment agent A and posttreatment agent B, the defects on the graphite surface and the bulk structure can be synergistically optimized. This adapts to the charge-discharge characteristics of anode-free sodium metal batteries, stabilizing sodium metal nucleophilic sites and achieving a highly efficient conductive interface. The modified current collector described in this invention effectively reduces irreversible sodium metal loss during cycling, guiding uniform sodium metal deposition / stripping, thereby significantly improving the long cycle life and high-temperature performance of anode-free sodium metal batteries.

[0016] In this invention, the conductive substrate includes a planar foil or a three-dimensional porous material, and the material includes at least one of copper, aluminum, and titanium.

[0017] The graphite has a diameter of 0.5~20μm and a D50 of 2~20μm; the degree of graphitization is 85~95%. The thickness is 50nm~500nm; more preferably 100~200nm.

[0018] In this invention, the MF n Special control over the types of graphite can be combined with other parameters to enhance the effect of graphite modification, thereby improving its electrochemical performance in negative electrode-free batteries.

[0019] MF in the first liquid-phase modification process n The preferred choice is CuF2; the preferred choice is MF. n It can work synergistically with other conditions and is expected to further enhance the electrochemical performance of electrodeless batteries.

[0020] In this invention, modifier A contains HF and MF. n The molar ratio is 1~5:1, more preferably 2~3:1; under the preferred ratio, it helps to combine and synergize, and enhance the electrochemical performance of the prepared anode-free material.

[0021] The solvent in the first liquid-phase modification process includes water. The concentration of HF in the first liquid-phase modification process is 0.2~0.5M, which can be further 0.25~0.4M; and even further 0.28~0.32M. Studies have shown that under the preferred conditions, it is helpful to synergistically enhance the electrochemical performance of the prepared anode-free material.

[0022] In the first stage of liquid-phase modification, the liquid-to-solid ratio is 1~15 ml / g; preferably 5~10 ml / g.

[0023] The temperature for the first stage of liquid-phase modification is 20~40℃, and the time is 3~6h.

[0024] In this invention, modifier B includes at least one of formulas 1A, 1B, and 1C;

[0025] Formula 1A;

[0026] Formula 1B;

[0027] Formula 1C;

[0028] Studies have shown that Formula 1A, and the combination of Formula 1A and Formula 1C, can be combined with other processes to enhance the modification effect and thus improve the electrochemical performance of anode-free batteries.

[0029] The solvent in the second-stage liquid-phase modification process includes water, ethanol, and oxalic acid, wherein the concentration of modifier B in the second-stage liquid-phase modification process is 0.2~0.5M.

[0030] In the second stage of liquid-phase modification, the mass ratio of water, ethanol, and oxalic acid in the solvent is 1:0.5~1.5:0.05~0.2.

[0031] In the second stage of liquid-phase modification, the liquid-to-solid ratio is 1~15 ml / g; preferably 5~10 ml / g.

[0032] The second stage of liquid-phase modification is performed at a temperature of 20~40℃ for 2~8 hours.

[0033] In this invention, the modified graphite, as a modifying material for a current collector without a negative electrode, operates differently from conventional ion batteries. Its function is not to provide sodium insertion / extraction sites, but rather to regulate the deposition / exfoliation behavior of sodium metal to improve its uniformity and reversibility.

[0034] In this invention, the modified coating further comprises an adhesive, wherein the adhesive includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide;

[0035] The modified coating contains 85-95 wt% modified graphite.

[0036] In this invention, the thickness of the modified coating is 50 nm to 500 nm; the loading of modified graphite is 0.1 to 0.8 mg / cm³. 2 Further, the concentration can be 0.25~0.5 mg / cm³. 2 .

[0037] The present invention also provides a modified negative electrode current collector, wherein the modified coating is formed on a conductive substrate by a coating or printing method.

[0038] The present invention also provides an application of the modified negative electrode current collector described above, using it as a negative electrode current collector for the preparation of a sodium metal battery without a negative electrode.

[0039] The present invention also provides a negative electrode-free sodium metal battery, comprising a battery cell and an electrolyte for soaking the battery cell, wherein the battery cell comprises a positive electrode, a separator and a current collector sequentially combined, and the current collector is the modified current collector described in the present invention.

[0040] The present invention also provides a positive electrode active material in the aforementioned positive electrode comprising at least one of a polyanionic compound, a transition metal oxide, and a Prussian blue compound;

[0041] The diaphragm includes at least one of glass fiber and polypropylene;

[0042] The electrolyte comprises a conductive sodium salt and an organic solvent.

[0043] The conductive sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium di(fluorooxalateborate).

[0044] The organic solvent includes carbonate and / or ether organic solvents; preferably, the carbonate organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate. The ether organic solvent includes at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, or 2-methyltetrahydrofuran.

[0045] The concentration of the conductive sodium salt in the electrolyte is 0.5~1.5M.

[0046] Beneficial effects

[0047] This invention innovatively composites modified graphite containing the aforementioned two stages of liquid-phase modification onto a conductive substrate. Based on the two-stage modification treatment using pretreatment agent A and posttreatment agent B, the defects on the graphite surface and the bulk structure can be synergistically optimized. This adapts to the charge-discharge characteristics of anode-free sodium metal batteries, stabilizing sodium metal nucleophilic sites and achieving a highly efficient conductive interface. The modified current collector described in this invention effectively reduces irreversible sodium metal loss during cycling, guiding uniform sodium metal deposition / stripping, thereby significantly improving the long cycle life and high-temperature performance of anode-free sodium metal batteries. Attached Figure Description

[0048] Figure 1 is a scanning electron microscope image of the modified composite current collector of Example 1;

[0049] Figure 2 shows the cycling stability of the electrodeless sodium metal battery assembled using the modified composite current collector in Example 1 at a current density of 300 mA / g.

[0050] Figure 3 shows the cycle stability of the anode-free sodium metal battery assembled using the modified composite current collector from Example 1 at a current density of 200 mA / g. Detailed Implementation

[0051] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the implementation of the present invention without creative effort are all within the scope of protection of the present invention.

[0052] Test conditions

[0053] The preparation process of the NFPP positive electrode is as follows: 0.9g of sodium iron pyrophosphate (NFPP) positive electrode material and 0.05g of conductive carbon black were weighed and ground together for 30 minutes to ensure uniform mixing. The mixed powder was transferred to a weighing bottle, and 1g of PVDF / NMP solution with a PVDF content of 5% (using N-methylpyrrolidone as solvent) and 1ml of supplementary NMP were added sequentially. The mixture was stirred continuously for 12 hours to form a uniform slurry. Using carbon-coated aluminum foil as the current collector, the obtained slurry was uniformly coated onto its surface. After being smoothed with a scraper, the slurry was placed in a vacuum drying oven and dried sequentially at 60℃ for 6 hours and 90℃ for 12 hours. Finally, the dried electrode was cut into round pieces with a diameter of 12 mm to obtain the NFPP positive electrode, with an active material loading of approximately 13 ± 1 mg / cm³. 2 .

[0054] The electrolyte for a negative electrode-free sodium metal battery was prepared as follows: 15.1 g of sodium hexafluorophosphate (NaPF6) and 0.109 g of sodium tetrafluoroborate (NaBF4) were accurately weighed and dissolved in 100 mL of diethylene glycol dimethyl ether (DEGDME). Then, 10 g of molecular sieve was added to adsorb any residual water in the solvent, resulting in a DEGDME-based electrolyte with a concentration of 0.9 M NaPF6 + 0.1 M NaBF4. The battery was assembled using a 19 mm diameter polyethylene membrane and a 19 mm glass fiber membrane, with the prepared positive electrode, electrolyte, and current collector as components. Battery testing was conducted at 30 °C, with a voltage window set to 1.5–3.9 V.

[0055] Example 1

[0056] Step 1:

[0057] Graphite sheets with a D50 of 5 μm and a graphitization degree of 92-93% were selected (the thickness of which was mainly distributed in the range of 150±10 nm accounted for more than 50%).

[0058] Step 2: Immerse the graphite from Step 1 in modification solution A and stir for 5 hours at room temperature; the modification solution A is an aqueous solution containing 0.15M metal fluoride (CuF2) and 0.3M HF (the liquid-to-solid ratio during the modification process is 5~15mL / g), and then the solid and liquid are separated and dried to obtain a modified material.

[0059] Step 3: Immerse a section of modified material in 0.3M modifier B (Formula 1A). In the modified solution B, the solvent in the modified solution B is a mixed solvent of water, ethanol and oxalic acid with a weight ratio of 1:1:0.1. The liquid-solid ratio in the modification process can be 5~10mL / g, the modification time is 5h, and then the solid-liquid separation and drying are used to obtain the two-stage modified material.

[0060] Step 4: Using the two-stage modified material as the active coating material, PVDF binder was added at 10% of the weight of the two-stage modified material powder. After dispersion with NMP, it was uniformly coated onto the surface of aluminum foil and dried at 80 ℃ for 12 h to obtain a composite current collector with a coating thickness of 8 μm and a loading of 0.3 mg / cm² (see Figure 1 for coating morphology). It was cut into discs with a diameter of 14 mm and assembled with an NFPP positive electrode and corresponding electrolyte to form a negative electrode-free sodium metal battery.

[0061] The electrochemical test results are shown in Figures 2 and 3: at current densities of 300 mA / g and 200 mA / g, the battery cycle life exceeded 1000 cycles. Among them, the capacity retention rates at 200 cycles at current densities of 300 mA / g and 200 mA / g reached 93.1% and 93.6%, respectively, indicating that the composite current collector has a significant modification effect and effectively improves the cycle stability of the battery.

[0062] Comparative Example 1:

[0063] Compared with Example 1, the only difference is that aluminum foil is directly used as the negative electrode current collector, while other operations and parameters are the same as in Example 1.

[0064] Comparative Example 2:

[0065] Compared with Example 1, the only difference is that the second-stage modification treatment in step 3 was not performed. Instead, the first-stage modified material in step 2 was used as the active material for the treatment in step 4. All other operations and parameters are the same as in Example 1.

[0066] Comparative Example 3:

[0067] Compared with Example 1, the only difference is that the modification treatment in step 2 was not performed. Instead, the graphite in step 1 was replaced with a portion of the material for the treatment in step 3. The graphite only underwent the first modification treatment. All other operations and parameters were the same as in Example 1.

[0068] Comparative Example 4:

[0069] Compared with Example 1, the only difference is that the graphite is pre-treated with the second stage of modification in step 3, and then the first stage of modification in step 2 is performed. All other operations and parameters are the same as in Example 1.

[0070]

[0071] The data in Table 1 clearly show that the negative electrode current collector coated with two-stage treated graphite can significantly improve battery performance.

[0072] Example 2

[0073] Compared with Example 1, the only difference is that in step 2, the type of metal fluoride is changed, as shown in Table 2; all other operations, parameters, and tests are the same as in Example 1. The results are shown in Table 2.

[0074]

[0075] When the preferred type of metal fluoride is CuF2, better performance of sodium metal batteries without a negative electrode can be obtained.

[0076] Example 3

[0077] Compared with Example 1, the only difference is that in step 2, the concentration of gold HF is changed; all other operations, parameters, and tests are the same as in Example 1. The results are shown in Table 3.

[0078]

[0079] A HF concentration of 0.3~0.4M can yield better performance of sodium metal batteries without a negative electrode.

[0080] Example 4

[0081] Compared with Example 1, the only difference is that the modifier B in step 3 is changed; all other operations, parameters, and tests are the same as in Example 1. The results are shown in Table 4.

[0082]

[0083] When the modifier B is of type 1A, combining formula 1A and formula 1B can yield better performance of sodium metal batteries without a negative electrode.

[0084] Example 5:

[0085] Compared with Example 1, the only difference is that the properties of graphite and the coating thickness are changed; all other operations, parameters, and tests are the same as in Example 1. The results are shown in Table 5.

[0086]

[0087] Controlling the particle size of graphite, especially keeping the D50 of graphite within 2~25μm, preferably 5~12μm, can yield better performance of sodium metal batteries without a negative electrode. Controlling the thickness of the modified coating within the range of 0.5~50 μm can significantly improve battery performance, with 5~20 μm being the best. In the range of 8~12 μm, the battery exhibits the best high-current cycle stability.

[0088] Example 6:

[0089] Compared to Example 1, the only difference is the battery testing temperature; all other operations, parameters, and tests are the same as in Example 1. The results are shown in Table 6.

[0090]

[0091] As can be seen from Examples 1 and 6, the negative electrode of the present invention has good high temperature resistance.

[0092] Comparative Example 2

[0093] Compared to Comparative Example 1, the only difference is the battery testing temperature; all other operations, parameters, and tests are the same as in Comparative Example 1. The results are shown in Table 7.

[0094]

[0095] As shown in Tables 9 and 10, the modified graphite coating with two-stage treatment can achieve better performance of high-temperature sodium metal batteries without negative electrodes.

Claims

1. A modified negative electrode current collector, comprising a conductive substrate and a modified coating composited thereon, characterized in that, The modified coating includes modified graphite; the modified graphite is obtained by pre-modifying graphite with modifier A in a first-stage liquid phase and then with modifier B in a second-stage liquid phase; modifier A includes HF and MF. n M includes at least one of Cu, Ag, Mg, and Ca, and n is the valence of M; the modifier B includes a compound with the structure of Formula 1. In Formula 1, R1 is a C1-C4 alkyl or phenyl group; R2 is an active group or a substituent with an active group; the active group is a hydroxyl, amino, or carboxyl group; a substituent with an active group refers to a substituent with the active group on a C1-C6 alkyl chain, benzene ring, or olefin chain.

2. The modified negative electrode current collector as described in claim 1, characterized in that, The conductive substrate includes a planar foil or a three-dimensional porous material, the material of which includes at least one of copper, aluminum, and titanium; the graphite has a diameter of 0.5~20μm and a D50 of 2~20μm; and the degree of graphitization is 85~95%.

3. The modified negative electrode current collector as described in claim 1, characterized in that, MF in the first liquid-phase modification process n The preferred form is CuF2; in modifier A, HF and MF are preferred. n The molar ratio is 1~5:1, more preferably 2~3:1; the solvent in the first liquid-phase modification process includes water, wherein the concentration of HF in the first liquid-phase modification process is 0.2~0.5M, more preferably 0.25~0.4M; even more preferably 0.28~0.32M; in the first liquid-phase modification, the liquid-solid ratio is 1~15ml / g; preferably 5~10ml / g; the temperature of the first liquid-phase modification is 20~40℃, and the time is 3~6h.

4. The modified negative electrode current collector as described in claim 1, characterized in that, Modifier B includes at least one of formulas 1A, 1B, and 1C; Formula 1A; Formula 1B; Formula 1C; Second paragraph The solvent in the liquid-phase modification process includes water, ethanol and oxalic acid. The concentration of modifier B in the second-stage liquid-phase modification process is 0.2~0.5M. In the second-stage liquid-phase modification, the liquid-to-solid ratio is 1~15ml / g, preferably 5~10ml / g. The second stage of liquid-phase modification is performed at a temperature of 20~40℃ for 2~8 hours.

5. The modified negative electrode current collector according to any one of claims 1 to 4, characterized in that, The modified coating further includes a binder, wherein the binder includes at least one of polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, and polyethylene oxide; and the modified graphite content in the modified coating is 85-95 wt%.

6. The modified negative electrode current collector as described in claim 1, characterized in that, The thickness of the modified coating is 50 nm to 500 nm; the loading of modified graphite is 0.1 to 0.8 mg / cm³. 2 .

7. A modified negative electrode current collector according to any one of claims 1 to 6, characterized in that, The modified coating is formed on a conductive substrate using a coating or printing method.

8. An application of the modified negative electrode current collector according to any one of claims 1 to 6, characterized in that, It was used as a negative electrode current collector to prepare a negative electrode-free sodium metal battery.

9. A negative electrode-free sodium metal battery, comprising a cell and an electrolyte for soaking the cell, wherein the cell comprises a positive electrode, a separator, and a current collector sequentially bonded together, characterized in that, The current collector is the modified current collector according to any one of claims 1 to 6.

10. The sodium metal battery without a negative electrode as described in claim 9, characterized in that, The positive electrode active material includes at least one of polyanionic compounds, transition metal oxides, and Prussian blue compounds; the separator includes at least one of glass fiber and polypropylene; the electrolyte includes a conductive sodium salt and an organic solvent; the conductive sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium di(fluorooxalate-borate); the organic solvent includes carbonate and / or ether organic solvents; preferably, the carbonate organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate; the ether organic solvent includes at least one of dimethoxymethane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, or 2-methyltetrahydrofuran; the concentration of the conductive sodium salt in the electrolyte is 0.5~1.5M.

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