Sodium ion battery

Abstract

The invention relates to the technical field of secondary batteries, in particular to a sodium ion battery. According to the sodium-ion battery, a polyanion compound and a layered metal oxide are compounded according to a certain proportion to serve as a positive electrode active material, amorphous hard carbon is matched to serve as a negative electrode active material, and the capacity ratio of a positive electrode to a negative electrode is regulated and controlled; through the synergistic effect of the positive and negative electrodes, the defects of the positive and negative electrode active materials are well overcome, so that the stability, the cycle life and the low-temperature performance of the sodium ion battery are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a sodium-ion battery. Background Technology

[0002] In recent years, lithium-ion batteries have become increasingly difficult to meet the needs of large-scale applications due to the high cost of raw materials, limited and uneven distribution of lithium resources. In contrast, sodium-ion batteries, with their abundant raw materials, wide geographical distribution, and low cost, and the ability to operate at temperatures ranging from -70°C to -100°C, are expected to become the next generation of high-performance batteries and have broad application prospects in technologies such as large-scale energy storage.

[0003] The overall performance and cost of sodium-ion batteries primarily depend on the positive and negative electrodes. The performance of these electrodes (such as specific capacity, voltage, and cycle life) is a key factor affecting the energy density, safety, and cycle life of sodium-ion batteries. Therefore, optimizing and designing the positive and negative electrodes to achieve synergistic effects and improve the overall performance of sodium-ion batteries is a current research hotspot. The positive and negative electrode active materials play a major role in these components. Positive electrode active materials for sodium-ion batteries mainly include layered metal oxides, polyanionic compounds, Prussian blue and its derivatives, and organic compounds. Among these, layered metal oxides suffer from structural instability, susceptibility to phase transitions, significant capacity decay during cycling, and short cycle life. Polyanionic compounds offer good safety and high voltage, but lack electron transport pathways, resulting in poor kinetics and conductivity. Negative electrode active materials for sodium-ion batteries mainly include amorphous hard carbon, titanium-based materials, alloy materials, and metal oxides. Amorphous hard carbon exhibits low initial coulombic efficiency, low rate capability, and poor cycle performance. Titanium-based materials have relatively low capacity. Alloy materials exhibit significant volume expansion and poor cycle performance after sodium intercalation. Metal oxides suffer from poor electrical conductivity and are prone to aggregation and irreversible conversion reactions.

[0004] The aforementioned positive and negative electrode active materials all have certain advantages and disadvantages. Therefore, how to overcome these defects and obtain sodium-ion batteries with better performance is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a sodium-ion battery that improves rate performance and cycle performance, as well as the performance of the sodium-ion battery at low temperatures, by optimizing and designing the positive and negative electrodes.

[0006] To achieve the above objectives, the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode active material comprises a polyanionic compound and a layered metal oxide, and the weight ratio of the polyanionic compound to the layered metal oxide is 1:0.5-2; the negative electrode active material comprises amorphous hard carbon; and the capacity ratio of the positive electrode to the negative electrode is 1:1.01-1.15.

[0007] The inventors of this invention have discovered that by combining polyanionic compounds and layered metal oxides in a certain proportion as positive electrode active materials, and simultaneously combining them with amorphous hard carbon as negative electrode active materials, and by controlling the capacity ratio of the positive and negative electrodes, the synergistic effect between them can effectively overcome the defects inherent in the aforementioned positive and negative electrode active materials, thereby greatly improving the stability, cycle life, and low-temperature performance of sodium-ion batteries. Detailed Implementation

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0009] This invention provides a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode active material comprises a polyanionic compound and a layered metal oxide, and the weight ratio of the polyanionic compound and the layered metal oxide is 1:0.5-2; the negative electrode active material comprises amorphous hard carbon; the capacity ratio of the positive electrode to the negative electrode is 1:1.01-1.15.

[0010] According to the present invention, a polyanionic compound and a layered metal oxide are used in combination as positive electrode active materials, while amorphous hard carbon is used as negative electrode active material. By adjusting the capacity ratio of the positive and negative electrodes, the synergistic effect between the positive and negative electrodes can overcome the defects of the positive and negative electrode active materials to a certain extent, thereby improving the rate capability, cycle performance, and low-temperature performance of the sodium-ion battery. To further enhance the synergistic effect between the positive and negative electrodes, reduce volume deformation and capacity decay during charging and discharging, and improve the specific capacity and conductivity of the positive and negative electrodes, preferably, the weight ratio of the polyanionic compound and the layered metal oxide is 1:0.5-1.5, more preferably 1:0.5-1, for example, values ​​such as 1:0.5, 1:0.6, 1:0.8, and 1:1, and any range between these values. Preferably, the capacity ratio of the positive electrode to the negative electrode is 1:1.01-1.12, more preferably 1:1.01-1.09, for example, it can be 1:1.01, 1:1.05, 1:1.07 and 1:1.09 and any range between these values.

[0011] According to the present invention, the polyanionic compound and the layered metal oxide can be selected from a wide range. To better synergize the polyanionic compound, the layered metal oxide, and the amorphous hard carbon, thereby enhancing the ion diffusion rate between the positive and negative electrodes and resulting in a sodium-ion battery with better electrochemical performance, preferably, the polyanionic compound is selected from one or more of Na8Fe4(P2O7)5, Na3V2(PO4)3, NaFePO4, and Na4Fe3(PO4)2P2O7, more preferably one or more of Na3V2(PO4)3, Na4Fe3(PO4)2P2O7, and Na8Fe4(P2O7)5. Preferably, the layered metal oxide is selected from Na... 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, Na 0.67 Mn 2 / 3 Fe 1 / 3 O2, NaFe 0.5 Co 0.5 O2, NaNi 0.5 Mn 0.5 O2 and Na 2 / 3Fe 0.5 Mn 0.5 One or more of O2, preferably Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, Na 0.67 Mn 2 / 3 Fe 1 / 3 O2 and Na 2 / 3Fe0.5 Mn 0.5 One or more of O2.

[0012] According to the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode material layer, the positive electrode material layer comprising the positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode current collector, the positive electrode conductive agent, and the positive electrode binder can be selected from a wide range of materials. The positive electrode current collector can be selected, for example, from one or more metal foils (e.g., aluminum foil). The positive electrode conductive agent can be selected, for example, from one or more of conductive graphite, SP conductive carbon black, conductive carbon fiber, carbon nanotubes, and Ketjen black, preferably from one or more of SP conductive carbon black, conductive carbon fiber, and carbon nanotubes. The positive electrode binder can be selected, for example, from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and gelatin, preferably from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, and gelatin. Preferably, the weight ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder is 70-95:0.1-2:0.1-1, for example, it can be 80:1.5:0.5, 72:2:0.8, 90:0.1:1 and 85:1:0.1 and any range between these values.

[0013] According to the present invention, the negative electrode comprises a negative electrode current collector and a negative electrode material layer, the negative electrode material layer comprising the negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode current collector, negative electrode conductive agent, and negative electrode binder can be selected from a wide range of materials. The negative electrode current collector can be selected, for example, from one or more metal foils (e.g., copper foil). The negative electrode conductive agent can be selected, for example, from one or more of conductive graphite, SP conductive carbon black, conductive carbon fiber, carbon nanotubes, and Ketjen black, preferably from one or more of SP conductive carbon black, conductive carbon fiber, and carbon nanotubes. The negative electrode binder can be selected, for example, from one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, and gelatin, preferably from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, and gelatin. Preferably, the weight ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is 75-110:0.1-2:0.2-3, for example, it can be 109:0.9:3, 100:2:2, 80:0.5:0.2 and 95:1:1.5 and any other values ​​between them.

[0014] According to the present invention, in preparing the positive electrode, the positive electrode active material, positive electrode conductive agent, and positive electrode binder can be mixed with a positive electrode solvent to form a positive electrode slurry, which is then coated onto the surface of the positive electrode current collector. The slurry is then subjected to rolling, slitting, and sheet-making processes to obtain the positive electrode sheet. The positive electrode solvent can be selected from a wide range. To ensure better mixing of the components, the positive electrode solvent is preferably selected from a mixture of an organic solvent and oxalic acid. Preferably, the organic solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide, ethyl nitrate, and N-methylpyrrolidone, more preferably N,N-dimethylformamide and / or N-methylpyrrolidone. Preferably, the volume ratio of the organic solvent to oxalic acid is 1:0.01-0.03, more preferably 1:0.01-0.02, for example, values ​​such as 1:0.01, 1:0.014, 1:0.018, and 1:0.02, and any range between these values. Preferably, relative to 1g of the positive electrode active material, the amount of the positive electrode solvent is 0.8-1.2mL, preferably 0.9-1.1mL, and can be, for example, 0.9mL, 0.95mL, 1mL, and 1.04mL, or any range thereof. In preparing the negative electrode, the negative electrode active material, negative electrode conductive agent, and negative electrode binder can be mixed with the negative electrode solvent to form a negative electrode slurry, which is then coated onto the surface of the negative electrode current collector. The slurry is then subjected to rolling, slitting, and sheet-making processes to obtain the negative electrode sheet. The negative electrode solvent can be water. Preferably, relative to 1g of the negative electrode active material, the amount of the negative electrode solvent is 0.9-1.2mL, preferably 1-1.1mL, and can be, for example, 1mL, 1.06mL, 1.08mL, and 1.1mL, or any range thereof.

[0015] According to the present invention, the compaction densities of the positive and negative electrodes can be selected within a wide range, as long as they are suitable for sodium-ion batteries. For better matching of the positive and negative electrodes and to obtain better electrical performance, preferably, the compaction density of the positive electrode is 1.8-3.2 g / cm³. 3 The preferred value is 2.3-2.9 g / cm³. 3 For example, it can be 2.3 g / cm³. 3 2.5g / cm 3 2.7g / cm 3 and 2.9g / cm 3 The numerical values ​​and the range between any given values. Preferably, the compacted density of the negative electrode is 0.6-1.2 g / cm³. 3 Preferably, it is 0.7-1.1 g / cm³. 3 For example, it can be 0.79 g / cm³. 3 0.85g / cm 3 0.9g / cm 3 and 1.1 g / cm3 The range between equal values ​​and any of them.

[0016] The positive and negative electrodes of the present invention can be applied to various sodium-ion batteries. However, in a preferred embodiment, the positive and negative electrodes of the present invention are more suitable for sodium-ion batteries with a median voltage of 2.9-3.05V, thereby achieving higher battery reliability and stability, as well as a longer cycle life. More preferably, the median voltage of the sodium-ion battery is 2.95-3.01V, for example, it can be 2.95V, 2.98V, 3V and 3.01V and any range between these values.

[0017] According to the present invention, the separator can be selected from a wide range, as long as it is suitable for sodium-ion batteries. To facilitate the synergistic effect between the positive and negative electrodes and further improve the stability and electrochemical performance of the sodium-ion battery, preferably, the separator can be selected from one or more of ceramic separators, aramid separators, polyethylene separators, polypropylene separators, and glass fiber separators, and more preferably from one or more of ceramic separators, aramid separators, and glass fiber separators.

[0018] According to the present invention, the electrolyte typically comprises a sodium salt, and the sodium salt and its concentration can be selected within a wide range. To facilitate sodium ion conduction and further improve the capacity retention and electrical performance of the sodium-ion battery, preferably, the sodium salt is selected from one or more of NaClO4, NaPF6, NaBF4, NaOTf, NaFSI, and NaTFSI, preferably NaClO4 and / or NaPF6. Preferably, the concentration of the sodium salt is 0.3-4 mol / kg, more preferably 0.8-3 mol / kg, for example, it can be 0.8 mol / kg, 1.5 mol / kg, 2 mol / kg, and 2.7 mol / kg, or any value within any range thereof.

[0019] According to the present invention, the electrolyte typically further includes a solvent, which can be selected from a wide range. To obtain an electrolyte with better performance, the solvent is preferably selected from one or more of ethylene carbonate, propylene carbonate, trimethyl phosphate, dimethyl carbonate, ethyl propionate, methyl propyl propionate, ethyl butyrate, ethyl 2,2,2'-trifluoroethyl acetate, difluoroethyl acetate, ethylene carbonate, fluoroethylene carbonate, butyl butyrate, propyl butyrate, and ethyl carbonate, and is more preferably selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl carbonate.

[0020] According to the present invention, the sodium-ion battery described above is preferably a cylindrical sodium-ion battery.

[0021] This invention uses a polyanionic compound and layered metal oxide in a certain ratio as the positive electrode active material, and amorphous hard carbon as the negative electrode active material. The capacity ratio of the positive and negative electrodes is controlled. By utilizing the synergistic effect between the positive and negative electrodes, the stability, cycle life and low temperature performance of sodium-ion batteries are greatly improved.

[0022] The present invention will be described in detail below through embodiments.

[0023] The methods and apparatus used in the following examples are conventional in the field, and the raw materials and reagents used are commercially available.

[0024] SP conductive carbon black was purchased from Wuxi Dongheng New Energy Co., Ltd.

[0025] Polyvinylidene fluoride was purchased from Zhejiang Funolin Chemical New Materials Co., Ltd.

[0026] Sodium carboxymethyl cellulose was purchased from Changshu Weiyi Technology Co., Ltd.

[0027] Amorphous hard carbon was purchased from BTR New Materials Group Co., Ltd.

[0028] The graphite was purchased from Shanghai Shanshan Technology Co., Ltd.

[0029] The ceramic diaphragm was purchased from Shanghai Enjie New Materials Technology Co., Ltd.

[0030] Examples 1-11

[0031] The positive electrode active material, negative electrode active material, and capacity ratios of the positive and negative electrodes in Examples 1-11 are shown in Table 1. The preparation process of the sodium-ion battery includes:

[0032] A positive electrode slurry was prepared by mixing positive electrode active material, SP conductive carbon black, and polyvinylidene fluoride at a mass ratio of 80:1.5:0.5 with a mixed solvent of N-methylpyrrolidone and oxalic acid (the volume ratio of N-methylpyrrolidone to oxalic acid was 1:0.02, and the amount of mixed solvent used was 1.04 mL relative to 1 g of positive electrode active material). The positive electrode slurry was coated onto the surface of aluminum foil, and a compaction density of 2.7 g / cm³ was obtained through rolling, slitting, and sheet forming processes. 3 The positive pole.

[0033] A negative electrode active material, SP conductive carbon black, and sodium carboxymethyl cellulose were mixed with water (1.06 mL relative to 1 g of negative electrode active material) at a mass ratio of 109:0.9:3 to form a negative electrode slurry. The negative electrode slurry was coated onto the surface of copper foil, and a compaction density of 0.79 g / cm³ was obtained through rolling, slitting, and sheet forming processes. 3 The negative electrode.

[0034] The prepared positive and negative electrodes were assembled with a ceramic separator and an electrolyte (2 mol / kg NaPF6 sodium salt and ethylene carbonate solvent) into a cylindrical sodium-ion battery. The median voltage range of the prepared sodium-ion battery was 2.95-3.01V.

[0035] Comparative Examples 1-8

[0036] The capacities of the positive electrode active material, negative electrode active material, and positive and negative electrodes in Comparative Examples 1-8 are shown in Table 1. The preparation process of the sodium-ion battery is the same as that in Examples 1-11.

[0037] Table 1

[0038]

[0039]

[0040] Test case

[0041] 1C cycle test: (1) Let stand at room temperature for 30 minutes; (2) Discharge with 1C to 1.8V; (3) Constant current with 1C to 3.9V and then constant voltage to cutoff current of 0.05C; (4) Let stand for 30 minutes; (5) Discharge with 1C to 1.8V; (6) Repeat steps (3) to (5) 1000 times.

[0042] 30C discharge test: (1) Let stand at room temperature for 30 minutes; (2) Discharge at 0.5C to 1.8V; (3) Constant current at 0.5C to 3.9V and then constant voltage to cutoff current of 0.05C; (4) Let stand for 30 minutes; (5) Discharge at 30C to 0V.

[0043] Low temperature discharge test: (1) Let stand at room temperature for 30 min; (2) Discharge at 0.5C to 1.8V; (3) Constant current at 0.5C to 3.9V and then constant voltage to cutoff current of 0.05C; (4) Let stand at -40℃ for 6.5 h; (5) Discharge at -40℃ at 0.5C to 1.8V.

[0044] -10℃ 0.1C / 1C cycle test: (1) rest at -10℃ for 6h; (2) discharge at 1C to 1.8V; (3) constant current at 0.1C to 3.9V and then constant voltage to cutoff current of 0.05C; (4) rest for 30min; (5) discharge at 1C to 1.8V; (6) repeat steps (3) to (5) 50 times.

[0045] The test results are shown in Table 2.

[0046] Table 2

[0047]

[0048]

[0049] As shown in Table 2, Examples 1-11, employing the technical solution of this invention, exhibit superior cycle performance, high-rate discharge performance, and low-temperature performance compared to Comparative Examples 1-8. Specifically, Examples 1-4 demonstrate a capacity retention rate exceeding 95% after 1000 cycles at 1C, can discharge for over 20 seconds at 30C current, and achieves over 80% of the initial discharge capacity at -40℃ (0.5C) compared to the initial discharge capacity at room temperature (0.5C). Furthermore, the capacity retention rate after 50 cycles at -10℃ (0.1C / 1C) also exceeds 80%. Therefore, the sodium-ion battery employing the technical solution of this invention exhibits excellent performance.

[0050] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode active material includes a polyanionic compound and a layered metal oxide, and the weight ratio of the polyanionic compound and the layered metal oxide is 1:0.5-2; the negative electrode active material includes amorphous hard carbon; the capacity ratio of the positive electrode to the negative electrode is 1:1.01-1.

15.

2. The sodium-ion battery according to claim 1, wherein, The weight ratio of the polyanionic compound to the layered metal oxide is 1:0.5-1.5, more preferably 1:0.5-1.

3. The sodium-ion battery according to claim 1 or 2, wherein, The capacity ratio of the positive electrode to the negative electrode is 1:1.01-1.12, more preferably 1:1.01-1.

09.

4. The sodium-ion battery according to any one of claims 1-3, wherein, The polyanionic compound is selected from one or more of Na8Fe4(P2O7)5, Na3V2(PO4)3, NaFePO4 and Na4Fe3(PO4)2P2O7, preferably one or more of Na3V2(PO4)3, Na4Fe3(PO4)2P2O7 and Na8Fe4(P2O7)5.

5. The sodium-ion battery according to any one of claims 1-4, wherein, The layered metal oxide is selected from Na. 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, Na 0.67 Mn 2 / 3 Fe 1 / 3 O2, NaFe 0.5 Co 0.5 O2, NaNi 0.5 Mn 0.5 O2 and Na 2 / 3 Fe 0.5 Mn 0.5 One or more of O2, preferably Na 0.9 Cu 0.22 Fe 0.30 Mn 0.48 O2, Na 0.67 Mn 2 / 3 Fe 1 / 3 O2 and Na 2 / 3 Fe 0.5 Mn 0.5 One or more of O2.

6. The sodium-ion battery according to any one of claims 1-5, wherein, The median voltage of the sodium-ion battery is 2.9-3.05V, preferably 2.95-3.01V.

7. The sodium-ion battery according to any one of claims 1-6, wherein, The electrolyte includes a sodium salt, which is selected from one or more of NaClO4, NaPF6, NaBF4, NaOTf, NaFSI, and NaTFSI, preferably NaClO4 and / or NaPF6.

8. The sodium-ion battery according to claim 7, wherein, The concentration of the sodium salt is 0.3-4 mol / kg, preferably 0.8-3 mol / kg.

9. The sodium-ion battery according to any one of claims 1-8, wherein, The electrolyte further includes a solvent selected from one or more of ethylene carbonate, propylene carbonate, trimethyl phosphate, dimethyl carbonate, ethyl propionate, propyl methyl propionate, ethyl butyrate, ethyl 2,2,2,-trifluoroethyl acetate, difluoroethyl acetate, ethylene carbonate, fluoroethylene carbonate, butyl butyrate, propyl butyrate, and ethyl carbonate, preferably one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl carbonate.

10. The sodium-ion battery according to any one of claims 1-9, wherein, The sodium-ion battery is a cylindrical sodium-ion battery.

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