A low temperature prussian white sodium-ion battery

Abstract

The application discloses a low-temperature Prussian white sodium ion battery, which comprises a positive electrode, an electrolyte and a negative electrode, the positive electrode is selected from a Prussian white positive electrode material; the electrolyte comprises a sodium salt, an organic solvent and an electrolyte additive; the concentration of the sodium salt in the electrolyte is 0.4-0.7 mol / L; and the electrolyte additive comprises a fluorinated carbonate and a fluorinated acetate. The low-temperature Prussian white sodium ion battery disclosed by the application has high specific capacity and long cycle life at a low temperature of-20 DEG C.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a low-temperature Prussian white sodium-ion battery. Background Technology

[0002] With the increasing severity of energy and environmental problems worldwide, the development of sustainable clean energy, such as wind, solar and tidal energy, has attracted widespread attention. However, these clean energy sources have the disadvantage of instability, that is, they are volatile with weather, climate and environment. Therefore, long-life, sustainable, inexpensive and environmentally friendly energy storage batteries are needed.

[0003] Currently, among numerous candidate batteries, lithium-ion batteries have become the mainstream energy storage battery due to their excellent overall performance, but they also face challenges related to resources and safety. In contrast, sodium-ion batteries have comprehensive advantages such as good safety, low cost, abundant resources, and environmental friendliness, making them very suitable for large-scale energy storage applications. As a cathode material for sodium-ion batteries, Prussian white material has advantages such as low cost and simple preparation.

[0004] For energy storage batteries, in addition to abundant resources, all-weather operation capability is required, especially excellent low-temperature performance to meet the needs of cold regions. Achieving excellent low-temperature performance requires innovation in materials, particularly cathode materials and electrolytes. Regarding materials, adding highly conductive agents, such as carbon nanotubes, or reducing particle size can promote charge transport to some extent, thereby improving low-temperature performance, but this increases manufacturing costs. As for electrolytes, high viscosity at low temperatures hinders sodium ion transport. One solution is to use special low-temperature organic solvents to reduce the viscosity of organic electrolytes at low temperatures; however, these solvents are generally expensive, leading to excessively high battery manufacturing costs, and they often cause adverse side reactions with electrode materials. Another solution is to reduce the concentration of sodium salts to lower electrolyte viscosity at low temperatures; however, reducing sodium salt concentration often sacrifices sodium ion mobility, and sodium ions themselves have a large ionic radius and atomic mass, resulting in low mobility, especially at low temperatures. Summary of the Invention

[0005] In view of the above-mentioned problems in the prior art, the present invention discloses a low-temperature Prussian white sodium-ion battery, which has high specific capacity and long cycle life at a low temperature of -20°C.

[0006] The specific technical solution is as follows:

[0007] A low-temperature Prussian white sodium-ion battery includes a positive electrode, an organic electrolyte, and a negative electrode.

[0008] The positive electrode is selected from Prussian white positive electrode material;

[0009] The electrolyte includes sodium salt, organic solvent, and electrolyte additives;

[0010] The sodium salt concentration in the electrolyte is 0.4–0.7 mol / L;

[0011] The electrolyte additives include fluorocarbonates and fluoroacetates.

[0012] This invention discloses a sodium-ion battery that uses Prussian white material as the positive electrode. By matching a special composition (adding special additives including fluorocarbonate and fluoroacetate) and a special content (controlling the sodium salt content in the electrolyte to 0.4-0.7 mol / L), the low-temperature performance of the sodium-ion battery is significantly improved.

[0013] The Prussian white cathode material used in this invention has a stable framework structure, with wide pores and channels for the diffusion of large-sized sodium ions, which is beneficial for the bulk diffusion of sodium ions at low temperatures, thereby improving low-temperature performance.

[0014] Preferably, the general chemical formula of the Prussian white cathode material is Na2M[Fe(CN)6], where M is selected from one or more of Ni, Fe, Mn, Zn, and Cu.

[0015] Preferably, M includes Mn, and manganese-based Prussian white has high capacity and operating voltage, which is beneficial to improving battery energy density; more preferably, Mn accounts for 50-70 mol% of the total M, and more preferably 60 mol%.

[0016] Further optimization revealed that M is selected from Mn, Fe, and Ni, with a molar ratio of 2.5–5.0:1.0–1.5:1. Experiments showed that sodium-ion batteries assembled using this cathode material, combined with a specially formulated and partially formulated organic electrolyte, exhibit superior low-temperature performance.

[0017] The Prussian white cathode material used in this invention can be prepared by conventional techniques in the field. Specifically, it is prepared by co-precipitation in an aqueous phase using sulfate, sodium ferrocyanide and complexing agent sodium citrate as raw materials.

[0018] The Prussian white cathode material prepared by this method exhibits a micro-nano structure, with secondary particles composed of primary particles ranging from 100 to 300 nm in size and 1 to 2 μm in diameter. This morphology is beneficial for increasing the interfacial area between the material and the electrolyte, promoting the diffusion of sodium ions at the interface, and also for inhibiting the corrosion of the material by the electrolyte, thereby further improving the low-temperature cycle life.

[0019] The electrolyte disclosed in this invention contains:

[0020] The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, and sodium bis(oxalato)borate; the concentration of sodium salt in the electrolyte is 0.4–0.7 mol / L.

[0021] Experiments have shown that within this concentration range, the electrolyte viscosity and ionic conductivity reach equilibrium, which is conducive to the diffusion of sodium ions in the electrolyte and at the material / electrolyte interface, thereby enabling sodium-ion batteries to achieve high capacity and stable cycling at low temperatures. If the sodium salt concentration range is too low or too high, the low-temperature stability of the prepared sodium-ion battery will decrease significantly.

[0022] Preferably, the sodium salt concentration in the electrolyte is 0.5 mol / L; with the optimization of the sodium salt concentration, the low-temperature stability of the finally assembled sodium-ion battery is further improved.

[0023] The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0024] Preferably, the organic solvent is selected from one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and a mixed solvent composed of propylene carbonate.

[0025] The preferred organic solvent of this invention contains propylene carbonate. Experiments have shown that when the organic solvent contains propylene carbonate, the prepared sodium-ion battery is more likely to achieve excellent low-temperature performance.

[0026] More preferably, the volume ratio of propylene carbonate to other organic solvents (one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) is 0.2 to 5:1; more preferably, it is 1:1.

[0027] The fluorocarbonate is selected from one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate;

[0028] The fluoroacetate is selected from one or more of ethyl trifluoroacetate, ethyl difluoroacetate, ethyl monofluoroacetate, methyl trifluoroacetate, and propyl trifluoroacetate.

[0029] Preferably, the mass ratio of fluorocarbonate to fluoroacetate is 3–9:1. Experiments have shown that when the two additives are controlled at this mass ratio, a stable protective layer can be formed on the negative electrode, and an ideal solvation structure can be formed with organic solvents and sodium ions. This reduces the binding force between organic solvent molecules and sodium ions, promotes sodium ion transport in the electrolyte at low temperatures, and facilitates rapid desolvation and transport at the material / electrolyte interface, significantly improving the low-temperature cycle performance of sodium-ion batteries. Experiments also revealed that if no electrolyte additives are added, or if only fluorocarbonate or fluoroacetate is added, the low-temperature performance of the assembled sodium-ion batteries significantly decreases.

[0030] Further preferred, the mass ratio of fluorocarbonate to fluoroacetate is 3–7:1; more preferably 4–7:1. With further optimization of the mass ratio, the low-temperature stability of the finally assembled sodium-ion battery is continuously improved.

[0031] Preferred:

[0032] The amount of electrolyte additives used is 1–8 wt% based on the total mass of the organic electrolyte.

[0033] Further preferred, the amount of electrolyte additive used is 2.5–8.0 wt%;

[0034] In this invention, by controlling the sodium salt concentration (0.4-0.7 mol / L) in the electrolyte and the amount of specific electrolyte additives (2.5-8.0 wt%), the assembled sodium-ion battery exhibits excellent low-temperature performance, with a capacity retention rate of not less than 91% after 500 cycles at -20°C and 1C current.

[0035] More preferably, the amount added is 5 to 8 wt%. With the optimization of the amount added, the low-temperature stability of the final assembled sodium-ion battery is further optimized.

[0036] The negative electrode is selected from low-voltage negative electrodes, including one or more of metallic sodium, soft carbon, hard carbon, hard carbon / soft carbon composite material, sodium / carbon composite material, and metal / carbon composite material.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention combines Prussian white cathode, low-concentration sodium salt, and low-dose electrolyte additives to achieve low electrolyte viscosity, rapid material / electrolyte interface diffusion rate, and rapid Prussian white bulk phase diffusion at low temperatures, thereby achieving high specific capacity and long cycle life of Prussian white-based sodium-ion batteries at low temperatures.

[0039] 2. The low-temperature Prussian white sodium-ion battery disclosed in this invention uses inexpensive Prussian white material cathode, low concentration of lithium salt and additives, which makes the battery low in cost, suitable for large-scale energy storage, and the battery manufacturing process is simple, short in cycle, low in energy consumption and suitable for mass production. Attached Figure Description

[0040] Figure 1 The charge-discharge curves of the sodium-ion battery prepared in Example 1;

[0041] Figure 2 The cycle life of the sodium-ion battery prepared in Example 1;

[0042] Figure 3 The cycle life of the sodium-ion battery prepared in Comparative Example 1 is shown.

[0043] Figure 4 The cycle life of the sodium-ion battery prepared in Comparative Example 2 is shown.

[0044] Figure 5 The cycle life of the sodium-ion battery prepared in Comparative Example 3 is shown.

[0045] Figure 6 The cycle life of the sodium-ion battery prepared in Comparative Example 4 is given. Detailed Implementation

[0046] The present invention will be described in further detail below with reference to embodiments and comparative examples, but the implementation of the present invention is not limited thereto.

[0047] Example 1

[0048] The composition of a sodium-ion battery: The positive electrode is Na2Mn. 0.6 Fe 0.2 Ni 0.2 The battery is assembled using [Fe(CN)6] as the negative electrode (sodium metal) and glass fiber as the separator. The electrolyte is a 0.5 mol / L NaPF6 solution of propylene carbonate / ethyl methyl carbonate (volume ratio 1:1) (with 4 wt% fluoroethylene carbonate and 1 wt% ethyl trifluoroacetate as additives).

[0049] The Prussian white cathode material is prepared using a co-precipitation method, specifically as follows:

[0050] Manganese sulfate, ferrous sulfate, and nickel sulfate were prepared according to a stoichiometric ratio and dissolved in a mixed solution of sodium citrate and sodium sulfate to obtain solution A. Sodium ferrocyanide was dissolved in deionized water according to a stoichiometric ratio to obtain solution B. Solution B was added dropwise to solution A at 60°C to carry out a co-precipitation reaction. After aging, centrifugation, washing, and vacuum drying, Prussian white cathode material was obtained.

[0051] The above-mentioned battery was subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. The charge-discharge curves at a current density of 0.1C (1C = 150mAh / g) are shown below. Figure 1 As shown, the initial charge and discharge capacities are 89.1 mAh / g and 89.6 mAh / g, respectively; after 500 cycles at 1C current, the capacity retention is 95.0%. Figure 2 .

[0052] The above-mentioned batteries were subjected to charge-discharge tests at room temperature, with a voltage range of 2–4V, and after 300 cycles at a 1C current, the capacity retention rate was 90.0%. (See attached data.) Figure 3 .

[0053] Therefore, it can be seen that the sodium-ion battery prepared by this invention has better low-temperature performance than room-temperature performance and can be used in low-temperature scenarios.

[0054] Comparative Example 1

[0055] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the concentration of NaPF6 in the electrolyte is replaced with 0.3 mol / L.

[0056] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. After 100 cycles at a 1C current, the capacity retention rate was 87.7%. (See attached data.) Figure 4 .

[0057] Comparative Example 2

[0058] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the concentration of NaPF6 in the electrolyte is replaced with 1.0 mol / L.

[0059] The above-mentioned battery was subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. After 50 cycles at 1C current, the capacity retention rate was 47.5%. (See attached data.) Figure 5 .

[0060] Comparing the capacity retention data of sodium-ion batteries prepared in Example 1 and Comparative Examples 1-2, it can be found that both excessively high and excessively low concentrations of sodium ions in the battery can lead to a significant decrease in battery cycle life.

[0061] Example 2

[0062] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the concentration of NaPF6 in the electrolyte is replaced with 0.4 mol / L.

[0063] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 93.8%.

[0064] Example 3

[0065] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the concentration of NaPF6 in the electrolyte is replaced with 0.7 mol / L.

[0066] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 94.2%.

[0067] Comparative Example 3

[0068] The composition of the sodium-ion battery is basically the same as that in Example 1, except that 4 wt% of fluoroethylene carbonate is added to the electrolyte, while ethyl trifluoroacetate is not added.

[0069] The above-mentioned battery was subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. After 50 cycles at 1C current, the capacity retention rate was only 11.9%. (See attached data.) Figure 6 .

[0070] As can be seen from the comparison between Example 1 and Comparative Example 3, the cycle life of the sodium-ion battery assembled in Comparative Example 3 is significantly reduced. This may be because, without the use of ethyl trifluoroacetate as an additive in the electrolyte, sodium ions do not form an ideal solvation structure, resulting in increased internal resistance of sodium ion transport and thus reduced cycle life.

[0071] Comparative Example 4

[0072] The composition of the sodium-ion battery is basically the same as that in Example 1, except that 1 wt% of ethyl trifluoroacetate is added to the electrolyte instead of fluoroethylene carbonate.

[0073] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 67.5%.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 4, the cycle life of the sodium-ion battery assembled in Comparative Example 4 is significantly reduced. This may be because when fluoroethylene carbonate is not added to the electrolyte, a stable SEI film is not formed on the negative electrode surface, resulting in a decrease in cycle life.

[0075] Comparative Example 5

[0076] The composition of the sodium-ion battery is basically the same as that in Example 1, except that no electrolyte additives are added to the electrolyte.

[0077] The above-mentioned battery was subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V. After 50 cycles at a 1C current, the capacity retention rate was only 6.8%.

[0078] Comparing Example 1 with Comparative Example 5, it can be found that the cycle life of the sodium-ion battery assembled in Comparative Example 5 is significantly reduced. This may be because without the electrolyte additives fluoroethylene carbonate and ethyl trifluoroacetate, neither an ideal solvation structure is formed nor an effective SEI film is formed on the negative electrode, resulting in increased battery internal resistance and a significant decrease in cycle life.

[0079] Example 4

[0080] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the electrolyte additives added are 7 wt% fluoroethylene carbonate and 1 wt% ethyl trifluoroacetate.

[0081] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 94.3%.

[0082] Example 5

[0083] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the electrolyte additives added are 1.9 wt% fluoroethylene carbonate and 0.6 wt% ethyl trifluoroacetate.

[0084] The above-mentioned batteries were charged and discharged at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 91.7%.

[0085] Example 6

[0086] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the electrolyte additives added are 4.5 wt% fluoroethylene carbonate and 0.5 wt% ethyl trifluoroacetate.

[0087] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 85.8%.

[0088] Comparative Example 6

[0089] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the electrolyte additives added are 2.5 wt% fluoroethylene carbonate and 2.5 wt% ethyl trifluoroacetate.

[0090] The above-mentioned batteries were charged and discharged at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at 1C current, the capacity retention rate was 77.5%.

[0091] Example 7

[0092] The composition of the sodium-ion battery is basically the same as that in Example 1, except that ethylene carbonate and methyl ethyl carbonate in a volume ratio of 1:1 are used as organic solvents in the electrolyte.

[0093] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at a 1C current, the capacity retention rate was 84.3%.

[0094] As can be seen from the comparison between Example 1 and Example 7, the cycle life of the sodium-ion battery assembled in Example 7 is reduced. This may be because when propylene carbonate is not used as a solvent, an effective solvation structure is not formed, which leads to an increase in battery internal resistance and a decrease in cycle life.

[0095] Comparative Example 7

[0096] The composition of the sodium-ion battery is basically the same as that in Example 1, except that the positive electrode is replaced with a material with the structural formula NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 layered material.

[0097] The above-mentioned batteries were charged and discharged at -20°C, with a voltage range of 2 to 4V, and after 500 cycles at 1C current, the capacity retention rate was 72.1%.

[0098] Comparing Example 1 with Comparative Example 7, it can be found that the special Prussian white framework structure of the present invention plays a key role in the low-temperature performance of the battery, and this structure is conducive to the rapid transport of sodium ions at low temperatures.

[0099] Example 8

[0100] The composition of a sodium-ion battery: The positive electrode is Na2Mn. 0.5 Fe 0.3 Ni 0.2 The battery is assembled using [Fe(CN)6] as the negative electrode (sodium metal) and glass fiber as the separator. The electrolyte is a propylene carbonate / dimethyl carbonate (1:1 volume ratio) solution of 0.5 mol / L NaClO4 (with 4 wt% difluoroethylene carbonate and 1 wt% ethyl difluorocarbonate as additives).

[0101] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. At a current density of 0.1C, the initial charge and discharge capacities were 86.3 mAh / g and 85.6 mAh / g, respectively. After 500 cycles at 1C, the capacity retention rate was 96.1%.

[0102] Example 9

[0103] The composition of a sodium-ion battery: The positive electrode is Na2Mn. 0.7 Fe0.15 Ni 0.15 The battery is assembled using [Fe(CN)6] as the negative electrode (sodium metal) and glass fiber as the separator. The electrolyte is a 0.5 mol / L NaBF4 solution of propylene carbonate / diethyl carbonate (volume ratio 1:1) (with 4 wt% trifluoromethyl ethylene carbonate and 1 wt% trifluoroacetate as additives).

[0104] The above-mentioned batteries were subjected to charge-discharge tests at -20°C, with a voltage range of 2–4V. At a current density of 0.1C, the initial charge and discharge capacities were 92.1 mAh / g and 91.6 mAh / g, respectively. After 500 cycles at 1C, the capacity retention rate was 91.5%.

[0105] Comparing Example 1 and Example 9, it can be seen that, due to Mn 3+ The Jahn-Teller effect means that increasing the manganese content leads to a decrease in cycle life.

[0106] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed methods.

Claims

1. A low-temperature Prussian white sodium-ion battery, comprising a positive electrode, an electrolyte, and a negative electrode, characterized in that: The positive electrode is selected from Prussian white positive electrode material; The electrolyte includes sodium salt, organic solvent, and electrolyte additives; The sodium salt concentration in the electrolyte is 0.4~0.7 mol / L; The electrolyte additives include fluorocarbonates and fluoroacetates. The fluorocarbonate is selected from one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate; The fluoroacetate is selected from one or more of ethyl trifluoroacetate, ethyl difluoroacetate, ethyl monofluoroacetate, methyl trifluoroacetate, and propyl trifluoroacetate. The amount of electrolyte additives used is 1~8 wt%, based on the total mass of the electrolyte as 100%.

2. The low-temperature Prussian white sodium-ion battery according to claim 1, characterized in that: The general chemical formula of the Prussian white cathode material is Na2M[Fe(CN)6], where M is selected from one or more of Ni, Fe, Mn, Zn, and Cu.

3. The low-temperature Prussian white sodium-ion battery according to claim 2, characterized in that: In the general chemical formula of the Prussian white cathode material, M is selected from Mn, Fe and Ni, and the molar ratio of the three is 2.5~5.0:1.0~1.5:

1.

4. The low-temperature Prussian white sodium-ion battery according to claim 1, characterized in that: The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium tetrafluoroborate, and sodium bis(oxalate-borate). The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

5. The low-temperature Prussian white sodium-ion battery according to claim 4, characterized in that: The organic solvent is selected from one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and a mixed solvent composed of propylene carbonate.

6. The low-temperature Prussian white sodium-ion battery according to claim 1, characterized in that: The mass ratio of fluorocarbonate to fluoroacetate is 3~9:

1.

7. The low-temperature Prussian white sodium-ion battery according to claim 6, characterized in that: The mass ratio of fluorocarbonate to fluoroacetate is 3~7:

1.

8. The low-temperature Prussian white sodium-ion battery according to claim 1, characterized in that: Based on the total mass of the electrolyte as 100%, the amount of electrolyte additive is 5~8wt%.

9. The low-temperature Prussian white sodium-ion battery according to claim 1, characterized in that: The negative electrode is selected from low-voltage negative electrodes, including one or more of metallic sodium, soft carbon, hard carbon, hard carbon / soft carbon composite materials, and metal / carbon composite materials.

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