A sodium supplement tablet and a secondary battery and its preparation method

Abstract

This invention discloses a sodium-supplementing sheet and a secondary battery and a method for preparing the same, comprising a support layer and a sodium-supplementing layer coated on the support layer. The support layer is made of at least one or more composites of polyolefins, polyimides, polyamides, ethylene-vinyl alcohol copolymers, polyvinylidene chloride, spandex or aramid, and ceramic membranes. This method can significantly improve initial efficiency and energy density, improve cycle stability, reduce capacity decay, and has a simple process that supports roll-to-roll continuous production.

Description

Technical Field

[0001] This invention relates to the field of sodium metal battery technology, specifically to a sodium supplement sheet, a secondary battery, and a method for preparing the same. Background Technology

[0002] Compared to lithium-ion batteries, sodium ions have a larger mass, resulting in lower energy density in traditional sodium-ion batteries. Furthermore, anode materials primarily composed of hard carbon and soft carbon irreversibly consume a large amount of sodium ions during the first charge / discharge cycle due to surface side reactions (forming a solid electrolyte interphase (SEI) film) and structural defects, leading to a generally low electrolyte concentration (ICE) (typically 60%-80%). This means that up to 20%-40% of the active sodium in the battery is permanently lost during initial use, directly lowering the overall battery energy density. Pre-sodiuming technology can replenish this lost sodium source in advance, making it the most direct and effective method to improve ICE and energy density.

[0003] Sodium-additive cathodes must meet a series of stringent requirements: high sodium content (to provide a sufficient sodium source), appropriate decomposition potential (below the upper limit of the cathode operating potential), high decomposition efficiency, harmless byproducts that do not affect battery performance, good air stability, and compatibility with existing processes. The decomposition potential must be matched; residues after decomposition may damage the electrode structure and affect cycle life, making industrialization difficult.

[0004] The negative electrode pre-sodiuming technology directly treats the negative electrode, pre-embedding sodium ions to compensate for irreversible consumption in subsequent cycles. It is more targeted and has high sodium replenishment efficiency. Depending on the treatment method, the negative electrode pre-sodiuming technology can be divided into direct contact method, electrochemical method and solution treatment method.

[0005] Patent CN 120473505 A developed a soft-contact pre-sodiuming technology to improve the uniformity and efficiency of pre-sodiuming: a trace amount of electrolyte is added between sodium metal and the negative electrode film layer as a "bridge" for sodium ion migration, and the contact is maintained for 0.5-2 hours under a certain pressure (1.6g-32g load). This method not only achieves efficient sodium ion compensation, but also removes and recovers unreacted sodium metal after pre-sodiuming, significantly improving safety and economy. However, sodium metal is relatively reactive in the drying room, posing certain safety hazards. The long contact time of 0.5-2 hours makes it difficult to improve the efficiency of mass production. Summary of the Invention

[0006] The purpose of this invention is to provide a sodium supplement sheet and a secondary battery and a method for preparing the same, which can significantly improve initial efficiency and energy density, improve cycle stability, reduce capacity decay, and has a simple process that supports roll-to-roll continuous production.

[0007] A sodium supplement sheet provided by the present invention includes a support layer and a sodium supplement layer coated on the support layer.

[0008] Furthermore, the material of the support layer is at least one or more composites of polyolefins, polyimides, polyamides, ethylene-vinyl alcohol copolymers, polyvinylidene chloride, spandex or aramid, and ceramic membranes.

[0009] Furthermore, the structure of the support layer adopts one or more composites of woven membranes, nonwoven membranes, extruded membranes, microporous membranes, and spun membranes.

[0010] Furthermore, the sodium-supplementing layer is made of a sodium alloy with the chemical formula NaXY, where X is a metallic element and Y is a non-metallic element, and the mass ratio of sodium element, metallic element X and non-metallic element Y is (75-98):(1-15):(1-10).

[0011] Furthermore, the metallic element X includes at least one of tin, gallium, bismuth, indium, and lithium, and the non-metallic element Y includes at least one of nitrogen, carbon, phosphorus, and sulfur.

[0012] The present invention also provides a method for preparing the sodium supplement tablets as described above, comprising the following steps: S1: Provides a support layer; S2: Melt sodium metal, add alloy phase components, mix evenly, and then add non-metallic materials to obtain a sodium-replenishing layer; S3: After melting the sodium-supplementing layer material, it is coated onto the support layer and collected by rolling to obtain the sodium-supplementing sheet.

[0013] The present invention also provides a secondary battery, comprising a positive electrode, a separator and a pre-sodiumized negative electrode stacked in sequence and filled with electrolyte.

[0014] Furthermore, the pre-sodium-treated negative electrode includes a negative electrode material layer and a current collector attached to the outside of the negative electrode material layer.

[0015] This invention also provides a method for preparing a secondary battery, comprising the following steps: A1: Both the positive electrode and the pre-sodium-treated negative electrode are ultrasonically welded with tabs and then baked. A2: The positive electrode, separator and pre-sodiumized negative electrode are wound and stacked in sequence; A3: After drying, a single formation process is performed followed by pre-packaging; A4: Secondary formation and secondary packaging are used to obtain a secondary battery.

[0016] Furthermore, prior to step A1, the process includes preparing the pre-sodium-treated negative electrode sheet, which comprises the following steps: B1: Provides the negative electrode plate; B2: The sodium-supplement sheet and the negative electrode material layer of the negative electrode sheet are bonded together, so that the sodium-supplement layer of the sodium-supplement sheet is in contact with the negative electrode material layer. After heating and rolling, the sodium-supplement sheet and the negative electrode sheet are subjected to self-discharge treatment, and then the sodium-supplement sheet is peeled off to obtain the pre-sodiumized negative electrode sheet.

[0017] The beneficial effects of this invention are as follows: 1. By precisely replenishing the sodium ions that are irreversibly consumed in the first cycle of the negative electrode, the initial efficiency and energy density are significantly improved. The ultra-thin sodium replenishment layer design reduces the proportion of inactive materials, further improving the energy density of the entire battery and solving the core problem that the energy density of sodium-ion batteries is lower than that of lithium-ion batteries.

[0018] 2. The alloy composition design of the sodium replenishment layer compensates for the loss of active sodium and interfacial side reactions. The pre-sodiumized negative electrode has a smaller volume change during cycling, which greatly reduces the capacity decay during battery cycling. Moreover, the sodium replenishment treatment does not have a negative impact on the battery cycling stability, improves cycling stability, and reduces capacity decay.

[0019] 3. Precise sodium source replenishment reduces the ineffective loss of sodium ions, significantly improving the charge utilization efficiency during battery charging and discharging, and further optimizing the battery's electrochemical performance. Attached Figure Description

[0020] Figure 1 This is a comparison chart of charge-discharge cycles for batteries #1, #2, #3, and #8.

[0021] Figure 2 The chart shows the rate performance test results for batteries #4, #5, and #9.

[0022] Figure 3 The above are the charge / discharge curves for batteries #6 and #7. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0024] The present invention provides a sodium supplementation tablet, comprising a support layer and a sodium supplementation layer coated on the support layer.

[0025] The material of the support layer is at least one or more composites of polyolefins, polyimides, polyamides, ethylene-vinyl alcohol copolymers, polyvinylidene chloride, spandex or aramid, and ceramic membranes.

[0026] The support layer is constructed using one or more composites of woven membranes, nonwoven membranes, extruded membranes, microporous membranes, and spun membranes.

[0027] It is worth noting that the thickness of the support layer is 3-55μm.

[0028] The sodium-filled layer is made of sodium alloy with the chemical formula NaXY, where X is a metallic element and Y is a non-metallic element. The mass ratio of sodium, metallic element X and non-metallic element Y is (75-98):(1-15):(1-10).

[0029] It is worth noting that the thickness of the sodium replenishment layer is 1-10 μm, corresponding to a replenishment capacity of 0.1 mAh·cm³. -2 -1mAh·cm -2 Surface capacity.

[0030] Metallic element X includes at least one of tin, gallium, bismuth, indium, and lithium, and non-metallic element Y includes at least one of nitrogen, carbon, phosphorus, and sulfur.

[0031] The present invention also provides a method for preparing the above-mentioned sodium supplement tablets, comprising the following steps: S1: Provides a support layer; S2: Melt sodium metal, add alloy phase components, mix evenly, and then add non-metallic materials to obtain a sodium-replenishing layer; S3: After melting the sodium-supplementing layer material, it is coated onto the support layer and collected by rolling to obtain the sodium-supplementing sheet.

[0032] It is worth noting that the alloy melting temperature is 200-450℃, and the non-metallic mixing temperature is 250-500℃. The melting point of the sodium-supplementing layer material is 90-150℃.

[0033] The present invention also provides a secondary battery, comprising a positive electrode, a separator and a pre-sodiumized negative electrode stacked in sequence and filled with electrolyte.

[0034] The pre-sodium-modified negative electrode includes a negative electrode material layer and a current collector attached to the outside of the negative electrode material layer.

[0035] This invention also provides a method for preparing a secondary battery, comprising the following steps: A1: Both the positive electrode and the pre-sodium-treated negative electrode are ultrasonically welded with tabs and then baked. A2: The positive electrode, separator and pre-sodiumized negative electrode are wound and stacked in sequence; A3: After drying, a single formation process is performed followed by pre-packaging; A4: Secondary formation and secondary packaging are used to obtain a secondary battery.

[0036] The process preceding step A1 includes preparing a pre-sodium-treated negative electrode sheet, which includes the following steps: B1: Provides the negative electrode plate; B2: The sodium-supplement sheet and the negative electrode material layer of the negative electrode sheet are bonded together, so that the sodium-supplement layer of the sodium-supplement sheet is in contact with the negative electrode material layer. After heating and rolling, the sodium-supplement sheet and the negative electrode sheet are subjected to self-discharge treatment, and then the sodium-supplement sheet is peeled off to obtain the pre-sodiumized negative electrode sheet.

[0037] It is worth noting that in step B2, the rolling pressure is 0.1-8MPa, the heating temperature is 60-150℃, and the rolling time is 5-60s. If the heating temperature is too low, the sodium supplement layer will embed slowly into the hard carbon layer of the negative electrode. If the temperature is too high, the sodium alloy will melt into small droplets and roll. The rolling time is adjusted according to the thickness of the sodium supplement layer and the heating temperature. The thinner the sodium supplement layer and the higher the temperature, the shorter the rolling time.

[0038] It is worth noting that in step B2, the theoretical areal capacity of the negative electrode sheet before pre-sodiumization on one side in step three is 1.5 mAh·cm³. -2 Up to 5mAh·cm -2 Based on the NP ratio (the ratio of the actual usable capacity of the negative electrode to the actual usable capacity of the positive electrode), which is generally between 1.1 and 1.5, the corresponding areal capacity of the positive electrode is approximately 1.0 mAh·cm³. -2 Up to 3.5mAh·cm -2 According to calculations, the initial efficiency of a full battery is generally 80-85% (based on the positive electrode), with a capacity loss of 0.1 mAh·cm³. -2 -1mAh·cm -2 The thickness of the sodium supplement layer corresponding to the areal capacity is approximately 1-10 μm. If the sodium supplement layer is too thin, the improvement is minimal, while if it is too thick, the overall energy density is reduced. Dynamic adjustments should be made based on the positive and negative electrode systems, with a slight excess of sodium supplement layer, even with capacity loss, being preferable (capacity loss...). 1.2 times).

[0039] Example 1 100 parts by mass of sodium metal were melted at 400℃, and then 14 parts by mass of tin metal were added. After mixing evenly, 10 parts by mass of conductive carbon were added and stirred evenly to obtain a sodium-supplementing layer melt with a melting point of 95℃. The melt was transferred to a coating hopper and heated to a coating temperature controlled at 100℃. The melt was then applied to a 10μm thick ceramic aramid film with a coating thickness controlled at 5μm to obtain the sodium-supplementing sheet material. Figure 2 As shown; the obtained sodium supplement sheet and negative electrode sheet are bonded together. The negative electrode sheet is a hard carbon electrode sheet that is well matched with the commercial sodium nickel manganese oxide (NFM) positive electrode sheet. The areal density of the positive electrode is 17.75 mg·cm³. -2 The N / P ratio is 1.1, and the single-sided areal capacity of the negative electrode is 2 mAh·cm³. -2 .

[0040] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the sodium-supplementing sheet into contact with the negative electrode material layer. The pre-sodiumized negative electrode sheet is obtained by heating and rolling at a pressure of 0.5 MPa and a heating temperature of 70°C for 5 seconds.

[0041] A pre-sodium-treated negative electrode was assembled with a positive electrode to form a full cell. The electrolyte used was 1.0M NaClO4 in EC:DMC:EMC=1:1:1 Vol% with 5.0% FEC, designated as cell number 1. A negative electrode without sodium addition was also assembled with a positive electrode to form a full cell, designated as cell number 2. The voltage window was 2-4V, and the charge / discharge rate was 0.1C. Cyclic charge / discharge tests were performed, and the data are shown below. Figure 1 .

[0042] It is worth noting that 1.0M NaClO4 in EC:DMC:EMC=1:1:1 Vol% with 5.0% FEC is the standard notation for describing electrolytes in the field of electrochemistry. Each part corresponds to the solute, solvent, additives, and their respective concentrations / ratios and volume percentages in the electrolyte. NaClO4 is sodium perchlorate, which is the sodium ion electrolyte salt of the electrolyte (this patent is for a sodium ion battery, so it is the core solute of the sodium ion source). Its function is to dissociate Na⁺ in the electrolyte and provide a carrier for ion migration during the charging and discharging process of the battery. 1.0M is a molar concentration, meaning that each liter of electrolyte contains 1.0 mole of sodium perchlorate; "in" indicates that the electrolyte salt is dissolved in the subsequent mixed organic solvent system. EC, DMC, and EMC are all commonly used carbonate organic solvents in electrolytes (non-aqueous solvents to avoid side reactions between water and sodium / electrode). EC is ethylene carbonate, which provides high ionic conductivity; DMC is dimethyl carbonate, which enhances the ion migration rate of the electrolyte. EMC is ethyl methyl carbonate, which balances dielectric constant and viscosity to optimize the overall performance of the electrolyte. 1:1:1 Vol% is a volume ratio, meaning that the three organic solvents EC, DMC, and EMC are mixed in a volume ratio of 1:1:1. "with" indicates the addition of functional additives to the above mixture. FEC: Fluorinated ethylene carbonate, is a film-forming additive for sodium electrolytes (SEI film). 5.0%: This means that the amount of FEC added is 5.0% of the total mass / volume of the electrolyte.

[0043] Example 2 100 parts by weight of sodium metal were melted at 400℃, followed by the addition of 12 parts by weight of tin metal and 2 parts by weight of gallium metal. After homogeneity, 10 parts by weight of conductive carbon were added and stirred until homogeneous, resulting in a sodium-supplementing layer melt with a melting point of 90℃. This melt was transferred to a coating hopper, and the coating temperature was controlled at 95℃. The melt was then applied to a 12μm polypropylene (PP) film, with a coating thickness controlled at 5μm. The resulting sodium-supplementing sheet material was obtained. This sodium-supplementing sheet was then bonded to a negative electrode sheet. The negative electrode sheet was a hard carbon electrode sheet well-matched to a commercially available sodium nickel manganese oxide (NFM) positive electrode sheet, with an areal density of 17.75 mg / cm³. 2 The N / P ratio is 1.1, and the single-sided areal capacity of the negative electrode is 2 mAh·cm³. -2 .

[0044] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the sodium-supplementing sheet into contact with the negative electrode material layer. The negative electrode sheet is then pre-sodiumized by heating and rolling at a pressure of 0.2 MPa and a heating temperature of 50°C for 10 seconds.

[0045] The pre-sodium-treated negative electrode and the positive electrode were assembled into a full cell. The electrolyte used was 1.0M NaClO4 in EC:DMC:EMC=1:1:1 Vol% with 5.0% FEC, designated as battery No. 3. Cyclic charge-discharge tests were conducted with a voltage window of 2-4V and a charge-discharge rate of 0.1C.

[0046] Example 3 100 parts by weight of sodium metal were melted at 450℃, followed by the addition of 12 parts by weight of tin metal and 2 parts by weight of lithium metal. After mixing thoroughly, 10 parts by weight of black phosphorus were added and stirred until homogeneous, resulting in a sodium-supplementing layer melt with a melting point of 115℃. This melt was transferred to a coating hopper, and the coating temperature was controlled at 120℃. The melt was then applied to 16μm polyimide (PI) substrate with a coating thickness controlled at 10μm to obtain the sodium-supplementing sheet material. The resulting sodium-supplementing sheet was then bonded to the negative electrode sheet. The negative electrode sheet was a hard carbon electrode sheet well-matched with commercial sodium vanadium phosphate (NVP) positive electrode sheets, and the areal density of the positive electrode was 20 mg / cm³. 2 The N / P ratio is 1.5, and the single-sided surface capacity of the negative electrode is 3 mAh·cm³. -2 .

[0047] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the sodium-supplementing sheet into contact with the negative electrode material layer. The pre-sodiumized negative electrode sheet is obtained by heating and rolling at a pressure of 1 MPa and a heating temperature of 90°C for 30 seconds.

[0048] The pre-sodium-treated negative electrode was assembled with the positive electrode to form a full cell. The electrolyte used was 1M NaPF6 in DME = 100 Vol%, designated as cell No. 4. The negative electrode without sodium was also assembled with the positive electrode to form a full cell, designated as cell No. 5. The voltage window was 2-4V. The test procedure was set as follows: 5 cycles of 0.1C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 1C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.1C charge / discharge, for rate performance testing.

[0049] Example 4 100 parts by weight of sodium metal were melted at 400℃, followed by the addition of 10 parts by weight of tin metal and 2 parts by weight of bismuth metal. After mixing thoroughly, 8 parts by weight of carbon black and 2 parts by weight of black phosphorus were added and stirred until homogeneous, resulting in a sodium-supplementing layer melt with a melting point of 130℃. This melt was transferred to a coating hopper, and the coating temperature was controlled at 135℃. The melt was then applied to 16μm polyimide (PI) with a coating thickness controlled at 8μm to obtain the sodium-supplementing sheet material. The resulting sodium-supplementing sheet was then bonded to the negative electrode sheet. The negative electrode sheet was a hard carbon electrode sheet that was well-matched to a commercially available sodium iron pyrophosphate (NFPP) positive electrode sheet, with an areal density of 20 mg / cm³. 2 The N / P ratio is 1.3, and the single-sided areal capacity of the negative electrode is 3 mAh·cm³. -2 .

[0050] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the negative electrode sheet into contact with the negative electrode material layer. The negative electrode sheet is then pre-sodiumized by heating and rolling at a pressure of 1 MPa and a heating temperature of 90°C for 30 seconds.

[0051] The pre-sodium-treated negative electrode was assembled with the positive electrode to form a full cell. The electrolyte used was 1M NaPF6 in DME=100 Vol%, which was designated as cell No. 6. The negative electrode without sodium was also assembled with the positive electrode to form a full cell, designated as cell No. 7. The voltage window was 2-4V, the charge-discharge rate was 0.5C, and a cyclic charge-discharge test was performed.

[0052] Example 5 100 parts by weight of sodium metal were melted at 400℃, followed by 14 parts by weight of tin metal. After mixing thoroughly, 10 parts by weight of conductive carbon were added and stirred until homogeneous, resulting in a sodium-replenishing layer molten liquid with a melting point of 95℃. This molten liquid was transferred to a coating hopper, and the coating temperature was controlled at 100℃. The mixture was then coated onto a 10μm thick ceramic aramid film, with the coating thickness controlled at 1μm, to obtain the sodium-replenishing sheet material. The resulting sodium-replenishing sheet was then bonded to a negative electrode sheet. The negative electrode sheet was a hard carbon electrode sheet well-matched to a commercially available sodium nickel manganese oxide (NFM) positive electrode sheet, with an areal density of 17.75 mg·cm³. -2The N / P ratio is 1.1, and the single-sided areal capacity of the negative electrode is 2 mAh·cm³. -2 .

[0053] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the sodium-supplementing sheet into contact with the negative electrode material layer. The pre-sodiumized negative electrode sheet is obtained by heating and rolling with a rolling pressure of 0.1 MPa and a heating temperature of 60℃ for 5 seconds.

[0054] The pre-sodium-treated negative electrode and positive electrode were assembled into a full cell. The electrolyte used was 1.0M NaClO4 in EC:DMC:EMC=1:1:1 Vol% with 5.0% FEC, which was designated as battery No. 8. The voltage window was 2-4V and the charge / discharge rate was 0.1C. Cyclic charge / discharge tests were conducted.

[0055] Example 6 100 parts by weight of sodium metal were melted at 450℃, followed by the addition of 12 parts by weight of tin metal and 2 parts by weight of lithium metal. After mixing thoroughly, 10 parts by weight of black phosphorus were added and stirred until homogeneous, resulting in a sodium-supplementing layer melt with a melting point of 115℃. This melt was transferred to a coating hopper, and the coating temperature was controlled at 120℃. The melt was then applied to 16μm polyimide (PI) substrate with a coating thickness controlled at 10μm to obtain the sodium-supplementing sheet material. The resulting sodium-supplementing sheet was then bonded to the negative electrode sheet. The negative electrode sheet was a hard carbon electrode sheet well-matched with commercial sodium vanadium phosphate (NVP) positive electrode sheets, and the areal density of the positive electrode was 20 mg / cm³. 2 The N / P ratio is 1.5, and the single-sided surface capacity of the negative electrode is 3 mAh·cm³. -2 .

[0056] The sodium-supplementing sheet and the negative electrode sheet are subjected to self-discharge treatment to bring the sodium-supplementing layer of the sodium-supplementing sheet into contact with the negative electrode material layer. The pre-sodiumized negative electrode sheet is obtained by heating and rolling at a pressure of 8 MPa and a heating temperature of 150°C for 60 seconds.

[0057] The pre-sodium-treated negative electrode and the positive electrode were assembled into a full cell. The electrolyte used was 1M NaPF6 in DME = 100 Vol%, designated as a No. 9 battery. The voltage window was 2-4V. The test procedure was set as follows: 5 cycles of 0.1C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 1C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.1C charge / discharge, for rate performance testing.

[0058] Table 1 Comparison of Battery Main Materials Comparative Example 1 Sodium metal was placed in a heating funnel, with the funnel temperature controlled at 100℃ and the heating coating temperature controlled at 95℃. The coating was then applied to a 10μm thick ceramic aramid film with a coating gap of 5μm. The molten sodium could not be coated on the support layer and formed spherical droplets. Even after changing to other support film substrates, the coatings remained sparse, and an ultrathin sodium-replenishing layer could not be obtained.

[0059] Comparative Example 2 After melting 100 parts by mass of sodium metal at 400℃, 10 parts by mass of conductive carbon were added and stirred. However, the non-metallic material could not be compatible with the sodium molten material, and the powder floated on the upper layer of the liquid, making it impossible to obtain a uniform sodium-filled molten solution.

[0060] Comparative Example 3 100 parts by mass of sodium metal were melted at 400℃, and then 14 parts by mass of tin metal were added. After mixing evenly, a sodium-replenishing layer melt with a melting point of 180℃ was obtained. The melt was transferred to a coating hopper and heated to a coating temperature controlled at 190℃. The melt was then applied to a 10μm thick ceramic aramid film. The coating thickness was controlled at 5μm. The contact angle with the support film was large, resulting in missed spots and uneven coating. Even after changing to other support film substrates (with excessively high melting points), the coating was still sparse and an ultra-thin sodium-replenishing layer could not be obtained.

[0061] Comparative Example 4 100 parts by weight of sodium metal were melted at 400℃, followed by the addition of 12 parts by weight of tin metal and 2 parts by weight of gallium metal. After thorough stirring, a sodium-replenishing layer molten liquid with a melting point of 130℃ was obtained. This molten liquid was transferred to a coating hopper, and the coating temperature was controlled at 135℃. The coating was then applied to a 16μm PI film (12μm polypropylene film cannot withstand 130℃), with a coating thickness controlled at 5μm. However, the large contact angle with the support film resulted in missed coating points and uneven coating. Even after changing to other support film substrates, the coating remained sparse, and an ultra-thin sodium-replenishing layer could not be obtained.

[0062] Depend on Figure 1 It is evident that when the pre-sodium-treated negative electrode is assembled into a full cell with the same positive electrode, under the same charge-discharge cycle test conditions, the first-cycle efficiency is increased from 77% to 99% compared to the non-pre-sodium-treated negative electrode (comparison between batteries #1 and #2). Calculated by the specific capacity of the positive electrode, the first-cycle discharge specific capacity increases from 82mAh / g to 105mAh / g, and the cycle stability is not affected by pre-sodium treatment. The pre-sodium-treated negative electrode can significantly improve the first-cycle efficiency of the hard carbon negative electrode in sodium-ion batteries, thereby increasing the energy density of the full sodium-ion battery.

[0063] As can be seen from the comparison between Examples 1-6 and Comparative Example 1, pure sodium cannot be used to prepare a qualified sodium replenishment layer. It must be modified by alloying. In Comparative Example 1, pure sodium molten liquid is directly coated on various support layers. The molten sodium is extremely amorphous with the support film and cannot be spread to form a uniform film. It only appears as spherical droplets and cannot be used to prepare an ultra-thin sodium replenishment layer of 1-10 μm. Examples 1-6 completely solved the coating problem of pure sodium by forming an alloy with metals such as tin / gallium / bismuth / lithium, and can obtain a uniform sodium supplement layer (5-10μm) on support layers such as ceramic aramid film, PP, and PI.

[0064] Secondly, as can be seen from the comparison between Examples 1-6 and Comparative Example 2, non-metallic materials need to be compounded with the sodium-metal alloy system. They are incompatible when directly added to pure sodium. In Comparative Example 2, conductive carbon was directly added to the pure sodium melt. The non-metallic materials and pure sodium were completely incompatible. The powder floated on the liquid surface and could not form a uniform sodium-filling molten liquid, making subsequent coating impossible. However, Examples 1-6 all followed a step-by-step preparation process from melting sodium to adding metal to form an alloy to adding non-metallic materials. The non-metallic materials (carbon black, black phosphorus) could be uniformly mixed with the sodium-metal alloy system to form a stable and uniform molten liquid, providing a basis for coating.

[0065] The addition of metallic elements is the key to achieving compatibility between nonmetals and sodium molten systems. The sodium-metal-nonmetal ternary system is the only feasible solution for preparing a uniform sodium-filled molten liquid.

[0066] Furthermore, Examples 1-4 are adaptation experiments of different parameters / components under the same sodium replenishment technology route. By making a horizontal comparison of the different adjustments of metal X combination, non-metal Y type, sodium replenishment layer thickness, matching positive and negative electrode systems, and rolling process parameters, the universality, controllability, and process adaptability of the sodium replenishment technology can be verified. At the same time, the influence of different component / parameter adjustments on sodium replenishment layer performance, process conditions, and battery adaptability can be clarified. Ultimately, it is proved that this technology can be finely customized according to actual industrialization needs and adapted to different sodium-ion battery systems. The sodium replenishment layer formulation system has extremely strong component controllability. The melting point of the sodium replenishment layer can be precisely controlled by fine-tuning the metal / non-metal components. All four examples are based on the Na-metal X-non-metal Y ternary alloy system. By adjusting the combination of metal X (pure Sn / Sn+Ga / Sn+Li / Sn+Bi) and the type of non-metal Y [conductive carbon / (carbon black + black phosphorus)], the melting point of the sodium replenishment layer can be achieved between 90℃ and 130℃. Precise control of the melting point range, by introducing low-melting-point Ga (Example 2), the melting point is reduced to the lower limit of the system at 90°C; by replacing / combining non-metallic Y (using carbon black + black phosphorus in Example 4), the melting point is increased to 130°C; the pure Sn + carbon black base system (Example 1) has a melting point of 95°C, taking into account both processability and stability. The fine-tuning of the components of the ternary system can achieve controllable adjustment of the core physicochemical properties (melting point) of the sodium supplement layer without changing the overall technical route, and adapt to different process temperature requirements.

[0067] The sodium replenishment process parameters can be dynamically matched with the performance of the sodium replenishment layer, resulting in high process flexibility and no fixed parameter limitations. In the six embodiments, the rolling pressure, heating temperature, and rolling time were adjusted according to the different melting points and thicknesses of the sodium replenishment layer, and all of them achieved efficient pre-sodiumization without any process failures. The sodium replenishment layer with a low melting point (Example 2, 90°C) was matched with a lower heating temperature (50°C), a smaller rolling pressure (0.2MPa), and a slightly longer rolling time (10s). High melting point and thick sodium replenishment layer (Examples 3 / 4, 115 / 130℃, 8 / 10μm): matched with higher heating temperature (90℃), greater rolling pressure (1MPa), and longer rolling time (30s); the thin sodium replenishment layer of the base system (Example 1, 95℃, 5μm) is matched with medium process parameters (0.5MPa, 70℃, 5s) to achieve short-time and efficient sodium replenishment. Therefore, the process parameters are not fixed values ​​and can be flexibly adjusted according to the actual performance of the sodium replenishment layer. Moreover, the adjustment rules are clear, which facilitates process debugging in the industrialization process.

[0068] The six embodiments are adapted to the two mainstream cathode systems of sodium-ion batteries, and cover designs with N / P ratios of 1.1-1.5 and negative electrode surface capacities of 2-3 mAh·cm³. -² Full range: Examples 1 and 2 use NFM (sodium nickel iron manganese oxide) cathodes with an N / P ratio of 1.1, a single-sided anode capacity of 2 mAh·cm⁻², and a sodium-filled layer thickness of 5 μm, making them suitable for battery systems with medium to low anode capacity and high matching degree. Examples 3 and 4 use NVP (sodium vanadium phosphate) cathodes with an N / P ratio of 1.5, a single-sided negative electrode capacity of 3 mAh·cm⁻², and a sodium supplement layer thickness of 8 / 10 μm, making them suitable for battery systems with higher surface capacity and greater negative electrode capacity redundancy.

[0069] Meanwhile, different cathode systems are also matched with special electrolytes (NaClO4 system for NFM, NaPF6 system for NVP), and the sodium replenishment layer can still achieve efficient pre-sodiumification. This sodium replenishment technology is not tied to specific cathode materials or electrolytes, and can be adapted to sodium-ion batteries of different specifications and systems in industrialization, with strong versatility.

[0070] Tin (Sn) is the core main component of metal X, while other metals (Ga / Li / Bi) are auxiliary modifying components. A small amount of these components can be added to achieve fine optimization of performance. In all six embodiments, Sn is the main component of metal X (accounting for more than 80% of the total mass of metal X), while Ga / Li / Bi are only added in trace amounts. Furthermore, the roles of the different auxiliary metals are clearly distinct, all serving to optimize the basic performance rather than replacing the core function of Sn. The core function of Ga (Example 2) is to further reduce the melting point and adapt to lower process heating temperatures; The core function of Li (Example 3) is to improve the intercalation compatibility of sodium ions with hard carbon anodes, and to adapt to anodes with higher areal capacity. The core function of Bi (Example 4) is to improve the chemical stability of sodium alloys, and to further optimize cycle compatibility when combined with composite nonmetal Y.

[0071] Sn's core modification function is to reduce surface tension, ensure coating properties, and reduce basic melting point, which is irreplaceable. Other metals are finely optimized components that can be selectively added according to actual needs to achieve a combination of "basic performance guarantee + personalized performance enhancement".

[0072] Compared with Comparative Example 3, which used a Na-Sn system without a third metal, its melting point is 180℃. The coating has a large contact angle, omissions, unevenness, and poor adhesion to the substrate. Example 1 used a Na-Sn system with a melting point of 95℃. The coating was uniform and there were no omissions. Comparative Example 4 used a Na-Sn-Ga system without a conductive phase / black phosphorus. The melting point is 130℃. The coating was uneven, with omissions and a large contact angle. Example 2 used a Na-Sn-Ga system with the addition of conductive carbon. The melting point is 90℃. It can be uniformly coated on the PP film.

[0073] Therefore, it can be seen that the melting point of the Na-Sn binary system is relatively high and the wettability is still insufficient. Introducing third metals such as Ga, Li, and Bi can further reduce the melting point and improve wettability. At the same time, adding conductive carbon / black phosphorus can further optimize the melt flow and interfacial compatibility, achieving uniform coating. The melting point of the sodium supplement layer is controlled in the range of 90-130℃, which is the suitable range for achieving ultra-thin uniform coating.

[0074] The sodium replenishment layer thickness can be dynamically adjusted according to the capacity loss during the first cycle of the battery to achieve precise sodium replenishment, balancing the sodium replenishment effect with the battery energy density. The sodium replenishment layer thickness (5μm, 8μm, 10μm) in the six embodiments is positively correlated with the negative electrode surface capacity and N / P ratio of the matched battery. Low areal capacity anode (2mAh・cm⁻², Examples 1 and 2): small capacity loss in the first cycle, matched with a 5μm thin sodium replenishment layer, which meets the sodium replenishment requirement while reducing the proportion of inactive materials; High areal capacity negative electrode (3mAh・cm⁻², Examples 3 and 4): The capacity loss is large in the first cycle. Matching with a slightly thicker 8 / 10μm sodium replenishment layer ensures sufficient sodium source and avoids insufficient sodium replenishment.

[0075] The core process of stepwise melt preparation, heated coating, and heated rolling self-discharge exhibits high stability. It can achieve uniform and efficient pre-sodiuming under different parameters. Although the four embodiments differ in composition, thickness, process parameters, and battery system, they all strictly follow the core process route of this patent and have successfully prepared a uniformly thick sodium-supplemented layer and a pre-sodiumed negative electrode sheet without uneven coating or insufficient sodium supplementation. The core process route is not designed for a specific parameter but is a universally applicable and stable process. As long as the parameters are adjusted within the range specified by the patent, the expected sodium supplementation effect can be achieved, providing a key guarantee for continuous and large-scale industrial production.

[0076] A comparison of Examples 1-6 shows that the melting temperature of the sodium-supplementing layer must match the thermal stability of the supporting base film. PP film is only suitable for low-temperature coating at <100℃; ceramic aramid and PI films are suitable for medium-high temperature coating at 95-135℃. Therefore, the type of base film determines the upper limit of the coating process temperature, which in turn limits the selection of the sodium-supplementing layer alloy system.

[0077] Combination Figure 1 , Figure 2 , Figure 3 , Figure 1The charge-discharge cycle diagrams for batteries #1, #2, #3, and #8 are shown. The negative electrode is a hard carbon electrode that is well matched with commercial sodium nickel iron manganese oxide (NFM) positive electrode. The areal density of the positive electrode is 17.75 mg·cm⁻², the N / P ratio is 1.1, and the single-sided areal capacity of the negative electrode is 2 mAh·cm⁻². The electrolyte used is 1.0 M NaClO₄ in EC:DMC:EMC=1:1:1 Vol% with 5.0% FEC. The voltage window is 2-4 V, and the charge-discharge rate is 0.1 C. Cyclic charge-discharge tests were conducted.

[0078] In the figure, battery #1 has an initial discharge capacity of 105.5 mAh / g and an initial efficiency of 99.5%; battery #2 has an initial discharge capacity of 81.7 mAh / g and an initial efficiency of 77%; battery #3 has an initial discharge capacity of 102 mAh / g and an initial efficiency of 96.5%; and battery #8 has an initial discharge capacity of 93.4 mAh / g and an initial efficiency of 88%.

[0079] Depend on Figure 1 It is evident that when the pre-sodium-treated negative electrode is assembled into a full cell with the same positive electrode, under the same charge-discharge cycle test conditions, the first-cycle efficiency is increased from 77% to 99% compared to the non-pre-sodium-treated negative electrode (comparison between batteries #1 and #2). Calculated by the specific capacity of the positive electrode, the first-cycle discharge specific capacity increases from 82mAh / g to 105mAh / g, and the cycle stability is not affected by pre-sodium treatment. The pre-sodium-treated negative electrode can significantly improve the first-cycle efficiency of the hard carbon negative electrode in sodium-ion batteries, thereby increasing the energy density of the full sodium-ion battery.

[0080] Figure 2 The rate performance test charts for batteries #4, #5, and #9 are shown. The test steps are set as follows: 5 cycles of 0.1C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 1C charge / discharge → 5 cycles of 0.5C charge / discharge → 5 cycles of 0.2C charge / discharge → 5 cycles of 0.1C charge / discharge.

[0081] The negative electrode is a hard carbon electrode that is well matched with commercial sodium vanadium phosphate (NVP) positive electrode. The electrolyte is 1M NaPF6 in DME=100 Vol%, the areal density of the positive electrode is 20mg / cm2, the N / P ratio is 1.5, and the single-sided areal capacity of the negative electrode is 3mAh·cm-2.

[0082] In the figure, the first discharge of battery #4 is 104.4 mAh / g, with an initial efficiency of 97.7%; the first discharge of battery #5 is 88 mAh / g, with an initial efficiency of 83%; and the first discharge of battery #9 is 103 mAh / g, with an initial efficiency of 97%. Batteries #4 and #5 exhibit good rate performance, with their charging and discharging curves basically overlapping throughout the rate performance test. However, the charging and discharging curves of battery #9 are basically overlapping at lower rates of 0.1C-0.2C, but overcharging occurs at higher rates. Battery #9 was produced by rolling at a pressure of 8 MPa, a heating temperature of 150℃, and a rolling time of 60 s to obtain a pre-sodium-treated negative electrode sheet. Compared to the No. 4 battery, increasing the rolling pressure does not affect the sodium replenishment effect, and the initial efficiency improvement is still considerable. Charge and discharge are normal at low rates. However, excessive rolling pressure may damage the bonding strength of the hard carbon in the negative electrode and the surface structure. At low rates, sodium metal slowly embeds into the negative electrode, and charge and discharge are unaffected. At high rates, it leads to slight overcharging, and the discharge capacity also decreases slightly, but it is still higher than the No. 5 battery without pre-sodium treatment.

[0083] Figure 3 The graphs show the charge-discharge curves of batteries #6 and #7. The test procedure was set to 0.5C charge-discharge cycle. In the graphs, the first discharge of battery #6 is 102.8 mAh / g, with an initial efficiency of 100%; the first discharge of battery #7 is 76 mAh / g, with an initial efficiency of 79%.

[0084] From the above Figures 1-3 It is known that pre-sodium treatment of hard carbon anodes can significantly improve the first coulombic efficiency and discharge capacity of sodium-ion batteries, and improve the overall electrochemical performance of the battery.

[0085] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A sodium supplement tablet, characterized by comprising: It includes a support layer and a sodium replenishment layer coated on the support layer.

2. The sodium supplement tablet according to claim 1, wherein The material of the support layer is at least one or more composites of polyolefins, polyimides, polyamides, ethylene-vinyl alcohol copolymers, polyvinylidene chloride, spandex or aramid, and ceramic membranes.

3. The sodium supplement tablet of claim 1, wherein The support layer is constructed using one or more composites of woven membranes, nonwoven membranes, extruded membranes, microporous membranes, and spun membranes.

4. The sodium supplement tablet of claim 1, wherein The sodium-supplementing layer is made of a sodium alloy with the chemical formula NaXY, where X is a metallic element and Y is a non-metallic element. The mass ratio of sodium, metallic element X, and non-metallic element Y is (75-98):(1-15):(1-10).

5. The sodium supplement tablet according to claim 4, wherein The metallic element X includes at least one of tin, gallium, bismuth, indium, and lithium, and the non-metallic element Y includes at least one of nitrogen, carbon, phosphorus, and sulfur.

6. A process for the preparation of a sodium supplement tablet according to any one of claims 1 to 5, characterised in that, Including the following steps: S1: Provides a support layer; S2: Melt sodium metal, add alloy phase components, mix evenly, and then add non-metallic materials to obtain a sodium-replenishing layer; S3: After melting the sodium-supplementing layer material, it is coated onto the support layer and collected by rolling to obtain the sodium-supplementing sheet.

7. A secondary battery characterized by comprising: It is formed by sequentially stacking a positive electrode, a separator, and a pre-sodiumized negative electrode and then filling them with electrolyte.

8. The secondary battery according to claim 7, characterized by The pre-sodium-treated negative electrode includes a negative electrode material layer and a current collector attached to the outside of the negative electrode material layer.

9. The method for preparing a secondary battery according to claim 8, characterized in that, Including the following steps: A1: Both the positive electrode and the pre-sodium-treated negative electrode are ultrasonically welded with tabs and then baked. A2: The positive electrode, separator and pre-sodiumized negative electrode are wound and stacked in sequence; A3: After drying, a single formation process is performed followed by pre-packaging; A4: Secondary formation and secondary packaging are used to obtain a secondary battery.

10. The method for preparing a secondary battery according to claim 9, characterized in that, Before step A1, the process further includes preparing the pre-sodium-treated negative electrode sheet, which includes the following steps: B1: Provides the negative electrode plate; B2: The sodium-supplement sheet and the negative electrode material layer of the negative electrode sheet are bonded together, so that the sodium-supplement layer of the sodium-supplement sheet is in contact with the negative electrode material layer. After heating and rolling, the sodium-supplement sheet and the negative electrode sheet are subjected to self-discharge treatment, and then the sodium-supplement sheet is peeled off to obtain the pre-sodiumized negative electrode sheet.

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