A sodium-ion battery pre-sodium negative electrode and a preparation method thereof

Abstract

The application relates to the technical field of batteries and discloses a sodium-ion battery pre-sodiumized negative electrode and a preparation method thereof. The sodium-ion battery pre-sodiumized negative electrode comprises a current collector and dry electrode films arranged on the two sides of the current collector; the dry electrode film is composed of a hard carbon negative electrode, a conductive agent, a binder and a sodium supplementing agent; the sodium supplementing agent is formed by vapor pre-sodiumizing a porous carbon and carrying out gas phase coating, provides an additional active sodium source in the first charging and discharging process, improves the first efficiency and the cycle performance of the battery; the dry electrode film is formed by uniformly dry mixing active particles, the conductive agent and the sodium supplementing material, adding the binder, and forming a self-supporting film under the fibrillation action of the binder, and finally, the self-supporting film is rolled and covered on the surface of the current collector. The application increases the compaction of the hard carbon negative electrode through the dry electrode process, improves the uniformity of the binder distribution, avoids the loss of the sodium supplementing material caused by the traditional slurry mixing process, improves the energy density, and reduces the manufacturing cost.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a pre-sodium-modified negative electrode for sodium-ion batteries and its preparation method. Background Technology

[0002] In recent years, with the continuous development and innovation of various new energy battery technologies, sodium-ion batteries have received increasing attention in research and industrialization as an electrochemical energy storage technology due to their abundant reserves, low cost, and excellent power performance. Currently, using hard carbon as the anode material for sodium-ion batteries has become a common choice for both research and industry. Hard carbon is inexpensive, has a lower sodium intercalation potential, and a higher theoretical capacity, making it a relatively ideal anode material for the industrialization of sodium-ion batteries. However, during the first charging cycle of a sodium-ion battery, hard carbon materials still form an SEI film, and sodium ions enter through structural defects, resulting in significant irreversible capacity loss after the first cycle. Furthermore, due to the disordered structural defects of hard carbon, it exhibits sodium adsorption and storage characteristics in the first half of the sodium-ion battery charging process, thus lacking a fixed potential plateau. Only in the subsequent half-cell discharge curve does the sodium ion intercalation plateau between the graphene layers become apparent. Pre-supplementing the hard carbon anode with sodium ions can effectively reduce the consumption of sodium ions in the cathode material and solvent, significantly extending the cycle life of sodium-ion batteries. This is of great significance for solving the industrial application of sodium-ion batteries. In recent years, pre-sodiuming strategies have been widely studied as a key strategy to compensate for capacity loss and improve electrochemical efficiency (ICE). Pre-sodiuming replenishes the irreversible sodium ion consumption during the first cycle of electrode materials through sodium doping or sodium-containing reagent reactions. Positive electrode pre-sodiuming aims to pre-replenish sodium ions transported to the negative electrode to prevent excessive consumption of positive electrode sodium ions and subsequent structural instability. Negative electrode pre-sodiuming directly replenishes the irreversible loss of sodium ions, and to prevent subsequent continuous consumption of sodium ions due to interfacial instability, the negative electrode typically needs to pre-form a high-quality solid electrolyte interface after sodium ion replenishment to maintain the beneficial effects of pre-sodiuming. Currently, the main pre-sodiuming strategies can be divided into direct contact, electrochemical pre-sodiuming, chemical reaction synthesis pre-sodiuming, and pre-sodiuming with sodium-containing additives. Different electrode materials employ different pre-sodiuming methods based on their structural defects, often leading to significant differences in electrochemical performance. Therefore, selecting an appropriate pre-sodiuming strategy for a specific electrode material is necessary and crucial. Summary of the Invention

[0003] The purpose of this invention is to provide a pre-sodium-modified negative electrode for sodium-ion batteries and its preparation method. The method involves forming a self-supporting film by using a dry process to combine active particles, conductive agents, and sodium-replenishing materials under the fibrillation effect of a binder. Finally, the film is rolled and covered onto the surface of the current collector to obtain the negative electrode sheet. This method avoids the loss of pre-sodium-modified reagents and the increase in alkalinity of the slurry caused by traditional slurry mixing. The pre-sodium agent replenishes the irreversible consumption of sodium ions during the first cycle in advance, giving sodium-ion batteries technical advantages such as high energy density, high rate capability, excellent cycle life, and low cost.

[0004] To achieve the above objectives, the present invention provides the following solution: On one hand, the sodium-ion battery pre-sodium-modified negative electrode of the present invention includes a current collector and dry electrode films disposed on both sides of the current collector; the dry electrode films are composed of a negative electrode active material, a sodium replenishing agent, a conductive agent and a binder. The negative electrode active material is hard carbon and / or soft carbon; The sodium supplement is prepared by high-temperature vaporization of metallic sodium to form sodium vapor, which is then combined with porous carbon to form pre-sodium, and then coated with a carbon layer in the gas phase to form a stable core-shell structure. The conductive agent includes any one or a combination of several of the following: carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, and graphene. The adhesive includes a fiberizable adhesive and a non-fiberizable adhesive, wherein the ratio of the fiberizable adhesive to the non-fiberizable adhesive in the adhesive is 70-95%: 5-30%.

[0005] Furthermore, the fiberable adhesive is modified with a surface carbon layer, and the fiberable adhesive includes any one or a combination of several of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, perfluoroethylene propylene, perfluoroalkylates, and perfluorosulfonic acid resins.

[0006] Furthermore, the mass ratio of the negative electrode active material, sodium supplement, conductive agent and binder is 93-96:1-3:1-2:2-5.

[0007] Furthermore, the porous carbon particles have a diameter of 3-7 μm and a micropore size of 1-5 nm.

[0008] Furthermore, the coating material used for the gas-phase coated carbon layer is a carbon-containing gaseous organic compound, including one or more of methane, acetylene, ethanol, methanol, acetaldehyde, and gaseous alkanes.

[0009] Furthermore, the sodium content of the coating material is 40-60%, and the specific capacity is 450-800 mAh / g.

[0010] On the other hand, the present invention also proposes a method for preparing a pre-sodium-modified negative electrode for sodium-ion batteries, comprising the following preparation steps: (1) After mixing the negative electrode active material, conductive agent, and sodium supplement, add the binder, and then apply an external high shear force to the dry mixture to make it disperse evenly; (2) Perform hot rolling 2-3 times to fibrillate the binder, turning it from an agglomerate into a network of fibrils, which then binds the electrode powder in a network manner. The mixture is then extruded to form a self-supporting film. (3) The self-supporting membrane is placed on the surface of the current collector and cured at 180°C using a hot roller press to achieve the composite of the electrode membrane and the current collector, thereby obtaining a dry electrode sheet with high pressure density.

[0011] Furthermore, the areal density of the dry-process electrode sheet in step (3) is 120-210 g / m³. 2 The compacted density is 1.0-1.2 g / cm³. 3 .

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The dry-process pre-sodium-modified negative electrode sheet of the present invention is composed of active material, conductive agent, binder and sodium replenishing agent. The active particles, conductive agent and sodium replenishing material are formed into a self-supporting film by the fibrillation of the binder through a dry process and then rolled onto the surface of the current collector. On the one hand, the exogenous sodium introduced on the negative electrode side compensates for the active sodium from the positive electrode side consumed by the negative electrode material in the formation of the SEI film during cell formation, solving the problem of low initial efficiency of hard carbon negative electrode and improving the initial coulombic efficiency and cycle stability of battery; on the other hand, the dry process with fibrillation of the binder results in fewer gaps between the active material and conductive agent, and can achieve a higher compaction density. The fibrillated network structure can suppress the volume expansion of the active material, prevent particles from falling off the current collector, enhance stability, and thus realize a high energy density and long life sodium-ion battery.

[0013] (2) The present invention adsorbs metallic sodium in porous carbon micropores by steam method, thereby reducing the defect degree of porous carbon core material. At the same time, the metallic sodium doping in the micropores compensates for the loss of active sodium in the positive electrode during the first charge and discharge, thereby improving the first efficiency. The amorphous carbon layer coated on the outer layer of the sodium replenisher has the characteristic of high electronic conductivity, which can reduce the defects on the material surface and improve the rate capability and cycle performance.

[0014] (3) The adhesive of the present invention is composed of a fibrous adhesive and a non-fibrillated polymer. First, by coating the surface of the fibrillated adhesive with conductive carbon, the adhesive is passivated and modified, thereby enhancing the conductivity of the active material, improving the stability of the adhesive, and inhibiting the decomposition of materials such as electrolytes. Second, by mixing with non-fibrillated materials, the particle size is reduced, uniformity is improved, and adhesion is enhanced. The particulate polymer (i.e., the non-fibrillated adhesive) can be incorporated into the dry electrode film at a certain particle size. Together with the fibrous adhesive, it can achieve close contact between the negative electrode active material, the conductive agent, and the adhesive. After compaction under dry conditions, there are fewer problems such as cracks and micropores. The fibrillated network structure can inhibit the volume expansion of the active material, prevent particles from falling off the current collector, enhance stability, and improve electrical performance.

[0015] (4) In this invention, the negative electrode active material, conductive agent, sodium supplementer and binder are uniformly mixed. Under the action of external shear force, the binder is fibrillated into a network to bond the electrode powder. The fibrillated powder is then repeatedly hot-rolled to form a self-supporting film. The self-supporting film is combined with the surface-treated current collector hot roller to prepare a high-load and high-compact dry pre-sodium-based negative electrode. The obtained sodium-based negative electrode has a uniform pore size and pore distribution, good uniformity and relatively high compaction density, which reduces the contact resistance and charge exchange impedance between the negative electrode materials, increases the ion migration rate, and is conducive to the insertion and extraction of sodium ions. This significantly improves the energy density of the battery and the utilization rate of the negative electrode material, thus obtaining an electrode structure with excellent energy density and rate performance. (5) The pre-sodium strategy prefers a dry electrode production environment. In the wet process, the solvent reacts with the pre-sodium additives, consuming active sodium, increasing battery impedance and weakening the pre-sodium effect. The dry process does not require solvents, and the dry production environment is more suitable for the needs of the pre-sodium strategy. Under the action of fibrillation, the dry electrode can achieve a smoother morphology than the wet electrode. The dry electrode can achieve a higher compaction density. This preparation method has simpler processing equipment and more reliable and easy on-site process control. It avoids the use of a large amount of harmful solvents, complex coating processes, and the influence of trace moisture in NMP on charge and discharge capacity, thus affecting cycle life and improving the electrical performance of the cell. It also avoids the problems of difficult binder fibrillation and complex equipment in the dry electrode process, thereby reducing the production cost and energy consumption of sodium-ion battery electrodes. The process steps are fewer, it is more environmentally friendly, and it is more suitable for large-scale production.

[0016] (6) The dry sodium-ion pre-sodium anode of the present invention has low cost, high loading capacity, high capacity, high first efficiency, high rate and excellent cycle performance. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments. Example 1

[0019] (1) Metallic sodium and porous carbon with a mass ratio of 2:1 are vaporized at high temperature to form sodium vapor and porous carbon composite pre-sodium, and then methane gas is introduced to form a carbon layer coating to form a pre-sodium agent with a stable core-shell structure.

[0020] (2) After mixing the negative electrode active material, sodium supplement, and conductive agent, add the binder in a mass ratio of 96.0:1.5:1.0:1.5. Then apply external high shear force to the dry mixture to make it disperse evenly. (3) Perform hot rolling 2-3 times to fibrillate the binder (from agglomerates to network fibrils) to form a network of bonded electrode powder. The binder consists of 95% PTFE and 5% CMC. Then, the mixture is extruded to form a self-supporting membrane.

[0021] (4) The prepared electrode film is placed on both sides of the current collector surface and cured at 180°C using a hot roller press to achieve the composite of the electrode film and the current collector, resulting in an area density of 210 μm. 2 / g, compacted density is 1.20g / cm³ 3 Dry pre-sodium-based negative electrode.

[0022] Then, a full cell was assembled and tested by combining it with an O3 layered transition metal oxide cathode. Example 2

[0023] (1) Metallic sodium and porous carbon with a mass ratio of 3:2 are vaporized at high temperature to form sodium vapor and porous carbon composite pre-sodium, and then acetylene gas is introduced to form a carbon layer coating to form a pre-sodium agent with a stable core-shell structure.

[0024] (2) After mixing the negative electrode active material, sodium supplement, and conductive agent, add the binder in a mass ratio of 94.5:2.0:1.0:2.5. Then apply external high shear force to the dry mixture to make it disperse evenly. (3) Perform hot rolling 2-3 times to fibrillate the binder (from agglomerates to network fibrils) to form a network of bonded electrode powder. The binder consists of 85% PTFE and 15% CMC. Then, the mixture is extruded to form a self-supporting membrane.

[0025] (4) The prepared electrode film is placed on both sides of the current collector surface and cured at 180°C using a hot roller press to achieve the composite of the electrode film and the current collector, resulting in an area density of 180 μm. 2 / g, compacted density is 1.10g / cm³ 3 Dry pre-sodium-based negative electrode.

[0026] Then, a full cell was assembled and tested by combining it with an O3 layered transition metal oxide cathode. Example 3

[0027] (1) Metallic sodium and porous carbon with a mass ratio of 1:1 are vaporized at high temperature to form sodium vapor and porous carbon composite pre-sodium, and then a mixture of methane and acetylene is introduced to form a carbon layer coating to form a pre-sodium agent with a stable core-shell structure.

[0028] (2) After mixing the negative electrode active material, sodium supplement, and conductive agent, add the binder in a mass ratio of 93.0:3.0:1.0:3.0. Then apply an external high shear force to the dry mixture to make it disperse evenly. (3) Perform hot rolling 2-3 times to fibrillate the binder (from agglomerates to network fibrils) to form a network of bonded electrode powder. The binder consists of 75% PTFE and 25% PVDF. Then, the mixture is extruded to form a self-supporting membrane.

[0029] (4) The prepared electrode film is placed on both sides of the current collector surface and cured at 180°C using a hot roller press to achieve the composite of the electrode film and the current collector, resulting in an area density of 160 μm. 2 / g, compacted density is 1.00g / cm³ 3 Dry pre-sodium-based negative electrode.

[0030] Then, a full cell was assembled and tested by combining it with an O3 layered transition metal oxide cathode. Example 4

[0031] The difference between Example 4 and Example 2 is that metallic sodium and porous carbon in a mass ratio of 2:1 are vaporized at high temperature to form sodium vapor and porous carbon composite pre-sodium, and then acetylene gas is introduced to form a carbon layer coating to form a stable core-shell structure pre-sodium agent. The remaining steps are the same as in Example 2. Example 5

[0032] The difference between Example 5 and Example 2 is that the negative electrode active material, sodium supplement, and conductive agent are mixed and then a binder is added in a mass ratio of 93.5:2.5:1.5:2.5. Then, a high external shear force is applied to the dry mixture to make it dispersed evenly. The remaining steps are the same as in Example 2. Example 6

[0033] The difference between Example 6 and Example 2 is that the adhesive consists of 90% PTFE and 10% CMC, while the remaining steps are the same as in Example 2.

[0034] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in step (2), no sodium supplement was added. The negative electrode active material and conductive agent were mixed and then added to the binder in a mass ratio of 96.0:1.5:2.5. The remaining steps are the same as in Example 1.

[0035] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that in step (3), only PTFE is used as the binder, and then the mixture is extruded to form a self-supporting membrane; the remaining steps are the same as in Example 2.

[0036] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that the traditional wet slurry mixing process is used. Specifically, the negative electrode active material, sodium supplement, and conductive agent are mixed and then added to the PVDF binder to form a slurry with a mass ratio of 94.5:2.0:1.0:2.5. Then, the mixture is coated and rolled to prepare a pre-sodium-treated negative electrode.

[0037] Table 1 below shows the performance data of sodium-ion batteries prepared by dry composite anodes of sodium-ion batteries in Examples 1-3 and Comparative Examples 1-3 of the present invention: Table 1 Sodium supplement capacity (mAh / g) Electrode compaction (g / cm3) First charge / discharge efficiency Energy density (Wh / kg) 500-week cycle retention rate Example 1 750.9 1.20 88.2% 159.3 95.2% Example 2 676.2 1.10 87.4% 152.8 94.5% Example 3 549.5 1.00 87.7% 152.5 94.6% Example 4 749.0 1.11 88.5% 156.7 95.5% Example 5 660.6 1.08 87.6% 155.6 95.1% Example 6 658.1 1.15 87.9% 156.2 94.6% Comparative Example 1 / 1.12 82.5% 136.4 91.8% Comparative Example 2 650.7 1.18 87.2% 151.2 93.5% Comparative Example 3 657.0 0.96 85.5% 141.1 92.2% As shown in Table 1, the sodium-ion batteries of Examples 1-6 exhibit high initial efficiency and energy density, as well as good cycle stability. Comparing Example 1 with Comparative Example 1, adding a sodium supplement to the negative electrode formulation to prepare a dry-process pre-sodiumized electrode sheet simultaneously improves the initial charge-discharge efficiency, cycle performance, and rate performance of the sodium-ion battery negative electrode, resulting in high sodium storage capacity. Comparing Example 2 with Comparative Example 2, the dry electrode fabrication process uses a composite of fibrous binder and small-particle polymer, leading to higher energy density, better rate performance, and better cycle stability in the sodium-ion battery. Comparing Example 2 with Comparative Example 3, the dry electrode process represents a comprehensive upgrade over the traditional wet process. In terms of manufacturing process, the dry electrode involves fewer steps, resulting in lower manufacturing costs and energy consumption. The raw materials are environmentally friendly, making it more suitable for large-scale production. Regarding battery performance, dry-process batteries can achieve higher energy density, and both electrical and mechanical properties are superior. The method of this invention is simple, easy to implement, and less prone to generating byproducts. In terms of applications, dry-process batteries are more suitable for the manufacturing needs of next-generation batteries such as solid-state batteries and 4680 batteries.

[0038] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A pre-sodium-modified negative electrode for a sodium-ion battery, characterized in that, It includes a current collector and dry electrode films disposed on both sides of the current collector; the dry electrode films are composed of a negative electrode active material, a sodium supplement, a conductive agent and a binder; The negative electrode active material is hard carbon and / or soft carbon; The sodium supplement is prepared by high-temperature vaporization of metallic sodium to form sodium vapor, which is then combined with porous carbon to form pre-sodium, and then coated with a carbon layer in the gas phase to form a stable core-shell structure. The conductive agent includes any one or a combination of several of the following: carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, and graphene. The adhesive includes a fiberizable adhesive and a non-fiberizable adhesive, wherein the ratio of the fiberizable adhesive to the non-fiberizable adhesive in the adhesive is 70-95%: 5-30%.

2. The sodium-ion battery pre-sodium-modified negative electrode according to claim 1, characterized in that, The fiberable adhesive is modified with a surface carbon layer, and the fiberable adhesive includes any one or a combination of several of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, perfluoroethylene propylene, perfluoroalkyl compounds, and perfluorosulfonic acid resins.

3. The sodium-ion battery pre-sodium-modified negative electrode according to claim 1, characterized in that, The mass ratio of the negative electrode active material, sodium supplement, conductive agent and binder is 93-96:1-3:1-2:2-5.

4. The sodium-ion battery pre-sodium-modified negative electrode according to claim 1, characterized in that, The porous carbon particles have a diameter of 3-7 μm and a micropore size of 1-5 nm.

5. The sodium-ion battery pre-sodium-modified negative electrode according to claim 4, characterized in that, The coating material used for the gas-phase coated carbon layer is a carbon-containing gaseous organic compound, including one or more of methane, acetylene, ethanol, methanol, acetaldehyde, and gaseous alkanes.

6. The sodium-ion battery pre-sodium-modified negative electrode according to claim 5, characterized in that, The coating material has a sodium content of 40-60% and a specific capacity of 450-800 mAh / g.

7. A method for preparing a pre-sodium-modified negative electrode for a sodium-ion battery as described in any one of claims 1-6, comprising the following preparation steps: (1) After mixing the negative electrode active material, conductive agent, and sodium supplement, add the binder, and then apply an external high shear force to the dry mixture to make it disperse evenly; (2) Perform hot rolling 2-3 times to fibrillate the binder into a mesh-like adhesive electrode powder, and then extrude the mixture to form a self-supporting film; (3) The self-supporting membrane is placed on the surface of the current collector and cured at 180°C using a hot roller press to achieve the composite of the electrode membrane and the current collector, thereby obtaining a dry electrode sheet with high pressure density.

8. The method for preparing a pre-sodium-modified negative electrode for a sodium-ion battery according to claim 7, characterized in that, The areal density of the dry-process electrode sheet in step (3) is 120-210 g / m³. 2 The compacted density is 1.0-1.2 g / cm³. 3 .