A coated Prussian blue analog material and sodium ion battery

Abstract

This invention discloses a coated Prussian blue analog material and a sodium-ion battery. The material consists of a Prussian blue analog matrix and a coating layer, wherein the chemical formula of the Prussian blue analog PBA is A. x M A [M B (CN)6] 1‑y ·□ y The coating consists of nH₂O (0≤x≤2, 0≤y<1, n≥0), with the coating being a transition metal oxide (MO) and / or a boride (MB). This invention coats Prussian blue analogues, effectively improving their structural stability as a cathode material during cycling without affecting electrochemical performance. When used in sodium-ion batteries, it enhances cycle stability and cycle life while maintaining specific capacity and rate performance. Furthermore, the preparation method provided by this invention can form a uniform coating layer on the surface of Prussian blue analogues, using readily available raw materials, and is simple to operate, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a coated Prussian blue analog material and its preparation method, as well as a sodium-ion battery using this material as the positive electrode material. Background Technology

[0002] In recent years, the global demand for power batteries and energy storage devices has grown rapidly. Lithium-ion batteries, due to their high conversion efficiency, fast response to load changes, and low maintenance requirements, have been widely used in electric vehicles and large-scale energy storage. However, the limited availability of lithium resources in lithium-ion batteries has led to a rapid and volatile increase in raw material prices, drastically increasing market risk. Sodium-ion batteries, with their abundant sodium reserves, suitable electrochemical potential, excellent low-temperature performance, and high rate performance, are considered the most effective complement to lithium-ion batteries. However, sodium-ion batteries still face challenges such as low energy density and poor cycle stability, lagging behind existing lithium-ion batteries and limiting their large-scale application.

[0003] Currently, the main cathode materials for sodium-ion batteries include layered transition metal oxides, polyanionic compounds, and Prussian blue analogs. Among them, Prussian blue analogs have a theoretical specific capacity (170 mAh / g) higher than polyanionic compounds and comparable to lithium iron phosphate; their cycle stability is better than that of layered oxides; and their synthesis method is convenient, as the product can be obtained through solution co-precipitation. Their material and process costs are very competitive, making them promising for applications. However, the presence of vacancy defects and lattice water causes the material structure to gradually collapse during cycling, resulting in capacity decay and decreased cycle stability, thus limiting their practical application.

[0004] As can be seen from the above, Prussian blue analogues are currently unable to achieve both high specific capacity and long-term cycling stability. Summary of the Invention

[0005] To address the current problem that Prussian blue analogues cannot simultaneously achieve high specific capacity and long cycle stability, this invention provides a coated Prussian blue analogue material, its preparation method, and its application as a cathode material in sodium-ion batteries.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect of the invention, a coated Prussian blue analog material is provided, the material comprising a Prussian blue analog matrix and a coating layer thereof, wherein the chemical formula of the Prussian blue analog matrix is ​​A. x M A [M B (CN)6] 1-y ·□ y·nH2O (0≤x≤2, 0≤y<1, n≥0), denoted as PBA; the coating layer is a transition metal oxide and / or boride, denoted as MO and MB; the coated Prussian blue analog material is denoted as MO / MB@PBA.

[0008] In the chemical formula of Prussian blue analogues, A is an alkali metal or alkaline earth metal cation, and M... A M B M is a transition metal cation. A M B Each is independently selected from at least one of Fe, Mn, Co, Ni, Cu, and Zn, M A and M B They can be the same or different; □ represents M. B (CN)6 cavity. The transition metal M in the transition metal oxide and / or boride used as the coating layer is selected from at least one of Fe, Co, Ni, and Cu.

[0009] The coating layer can be a transition metal oxide or a transition metal boride, or a composite of transition metal oxides and transition metal borides, preferably at least one selected from FeO, Fe2O3, FeB, CoO, Co2O3, CoB, NiO, NiB, CuO, and CuB. The coating layer accounts for 0.5% to 10 wt% of the total mass of the material, and the coating layer thickness is approximately 5 to 10 nm.

[0010] Furthermore, the coated Prussian blue analogue material is a face-centered cubic crystal with a particle size of 400–600 nm.

[0011] Furthermore, the preferred ranges for x, y, and n are 1.7 ≤ x ≤ 2, 0 ≤ y ≤ 0.2, and 0 ≤ n ≤ 3.

[0012] In a second aspect of the present invention, a method for preparing the above-mentioned coated Prussian blue analog material is provided, comprising the following steps:

[0013] 1) Preparation of Prussian blue analogues;

[0014] 2) Prussian blue analogues and transition metal M salts are reacted in solution to obtain coated Prussian blue analogue materials.

[0015] Step 1) above can be used to prepare Prussian blue analogues by solution coprecipitation, that is, sodium ferrocyanide or sodium ferricyanide and transition metal M A Prussian blue analogues were obtained by precipitation using salts, chelating agents, and antioxidants, specifically including:

[0016] 1a) Transition metal M ASalt, chelating agent, and antioxidant are dissolved in a solvent in a certain proportion to obtain solution A; wherein, transition metal M A The molar ratio of salt to chelating agent is in the range of 1:1 to 1:10, preferably 1:4 to 1:6; the antioxidant accounts for a certain percentage of the transition metal M. A 1% of the total mass fraction of salt and chelating agent;

[0017] 1b) Dissolve sodium ferrocyanide or sodium ferricyanide and a chelating agent in a solvent in a certain proportion to obtain solution B; wherein, the molar ratio of sodium ferrocyanide or sodium ferricyanide to the chelating agent is in the range of 1:0 to 1:10, preferably 1:0 to 1:3;

[0018] 1c) Under an inert atmosphere, solution A is added to solution B at a certain rate, and the mixture is stirred and reacted at 0–100°C for 0.5–24 h; wherein the addition rate of solution A is 0.4%–4% per minute, preferably 0.6%–1.5%;

[0019] 1d) After the reaction is complete, age the mixture at 0–100°C for 0.5–24 h under static conditions;

[0020] 1e) After aging, the product is vacuum dried at 80–150°C to obtain a Prussian blue analogue.

[0021] The solvent mentioned in steps 1a) and 1b) above can be water, or a mixture of water and ethanol.

[0022] Preferably, the transition metal M A The salt is selected from one or more of iron salts, manganese salts, cobalt salts, nickel salts, copper salts, and zinc salts, wherein the salt is a sulfate and its hydrate, a nitrate and its hydrate, a chloride and its hydrate, an acetate and its hydrate, or an oxalate and its hydrate.

[0023] Preferably, the chelating agent is selected from one or more of sodium citrate, disodium ethylenediaminetetranitrite, sodium diethylenetriaminepentamethylphosphonate, sodium carboxymethyl cellulose, sodium gluconate, and sodium pyrophosphate.

[0024] Preferably, the antioxidant is selected from one or more of ascorbic acid, glutathione, vitamin E, and melatonin.

[0025] Preferably, the inert atmosphere in step 1c) is either nitrogen or argon.

[0026] Step 2) above specifically includes:

[0027] 2a) A solution C is obtained by mixing a Prussian blue analogue and a transition metal M salt in a solvent at a certain ratio; wherein the molar ratio of the Prussian blue analogue and the transition metal M salt is 1:0.01 to 1:0.2, preferably 1:0.05 to 1:0.1;

[0028] 2b) Dissolve sodium borohydride and / or sodium hydroxide in a solvent at a certain concentration to obtain solution D; wherein the mass fraction of sodium borohydride in solution D is 1% to 20%, and / or the mass fraction of sodium hydroxide is 1% to 5%; the molar ratio of transition metal M salt contained in solution C to sodium borohydride and / or sodium hydroxide contained in solution D is 1:1 to 1:2.

[0029] 2c) Add solution D to solution C at a certain rate and react at 0–100°C for 0.5–24 h with stirring; wherein the addition rate of solution D is 0.8%–6% per minute, preferably 2%–4%;

[0030] 2d) After the reaction is complete, the mixture is centrifuged and the precipitate is vacuum dried at 80-150°C to obtain coated Prussian blue analog material.

[0031] Preferably, the solvent in steps 2a) and 2b) is a mixture of water and ethanol, with ethanol accounting for 0-60% of the total mass of the solvent; it can also be anhydrous ethanol, methanol, tetrahydrofuran, or other solvents that do not react with sodium borohydride or sodium hydroxide.

[0032] Preferably, the transition metal M salt is one or more of iron salt, cobalt salt, nickel salt, and copper salt, wherein the salt is one or more of sulfate and its hydrate, nitrate and its hydrate, chloride and its hydrate, acetate and its hydrate, and oxalate and its hydrate.

[0033] In a third aspect of the invention, a sodium-ion battery is provided that uses the aforementioned coated Prussian blue analog material as the positive electrode material. The sodium-ion battery includes a positive electrode, a negative electrode, and an electrolyte, and its assembly form includes, but is not limited to, button cells, pouch cells, and cylindrical cells. The positive electrode is made of the aforementioned coated Prussian blue analog material, and the negative electrode can be selected from sodium metal and hard carbon. Battery assembly is performed in an argon-atmosphere glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0034] This invention provides a coated Prussian blue analog material MO / MB@PBA, a method for preparing the material, and a sodium-ion battery using the material as a cathode material, which has the following beneficial technical effects:

[0035] 1. The material provided by this invention coats Prussian blue analogues, which effectively improves the structural stability of Prussian blue cathode materials during cycling without affecting electrochemical performance.

[0036] 2. The preparation method provided by the present invention can form a uniform coating layer on the surface of Prussian blue analogues, the raw materials are readily available, and the method is simple.

[0037] 3. The coated Prussian blue analog material of the present invention, when used in sodium-ion batteries, improves the cycle stability and cycle life of sodium-ion batteries while ensuring the specific capacity and rate performance of sodium-ion batteries. Attached Figure Description

[0038] Figure 1 This is the XRD pattern of the coated Prussian blue analog material prepared in Example 1.

[0039] Figure 2 This is a SEM image of the coated Prussian blue analog material prepared in Example 1.

[0040] Figure 3 This is a schematic diagram of the coating structure of the coated Prussian blue analog material prepared in Example 1.

[0041] Figure 4 This is a comparison graph of the cycle performance of sodium-ion batteries in Example 1 and Comparative Example 1 at low current density.

[0042] Figure 5 This is a comparison graph of the cycle performance of sodium-ion batteries under high current density in Example 1 and Comparative Example 1.

[0043] Figure 6 This is a comparison graph of the cycle performance of sodium-ion batteries in Example 2 and Comparative Example 1 at low current density. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to examples. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention, but the examples are not intended to limit the invention. Unless otherwise specified, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] Example 1

[0046] (1) Weigh 7 mmol FeSO4·7H2O, 35 mmol sodium citrate and 0.1 g ascorbic acid and dissolve them in 80 mL of deionized water to obtain solution A;

[0047] (2) Weigh 7 mmol of Na4Fe(CN)6·10H2O and dissolve it in 60 mL of deionized water to obtain solution B;

[0048] (3) Under magnetic stirring and a nitrogen atmosphere, solution A was injected into solution B using a syringe pump. The magnetic stirring speed was set to 500 rpm and the injection rate to 0.5 mL / min. -1 ;

[0049] (4) After injection, continue stirring for 2 hours, then age for 4 hours;

[0050] (5) After aging, centrifuge and wash with deionized water 3 times. The centrifugation program is 10,000 rpm for 5 minutes.

[0051] (6) The product from step (5) was placed in a vacuum oven at 120°C and vacuum dried for 12 hours to obtain Prussian blue cathode material PBA, with the chemical formula Na. 1.73 Fe[Fe(CN)6] 0.82 ·2.28H2O;

[0052] (7) Weigh 0.3g of NaOH and dissolve it in a mixed solvent of 30mL of deionized water and anhydrous ethanol (volume ratio 1:1), and record it as solution C;

[0053] (8) Weigh 1.0g PBA and 0.05g Co(NO3)2 and disperse them in a mixed solvent of 40mL deionized water and anhydrous ethanol (volume ratio 1:1), and record it as solution D. Stir thoroughly for 1h.

[0054] (9) Under magnetic stirring, solution C was injected into solution D using a syringe pump at a rate of 0.3 mL / min. -1 ;

[0055] (10) After injection, continue stirring for 2 hours;

[0056] (11) After completion, centrifuge and wash 3 times with mixed solvent. The centrifugation program is 10,000 rpm for 5 min.

[0057] (12) The product from step (11) was placed in a vacuum oven at 120°C and vacuum dried for 12 hours to obtain the coated Prussian blue analog material CoO@PBA.

[0058] Figure 1 The X-ray diffraction (XRD) pattern of CoO@PBA prepared in Example 1 is shown, revealing the typical face-centered cubic structure of the material. Figure 2 The image shown is a scanning electron microscope (SEM) image of CoO@PBA prepared in Example 1. It can be seen that the particle size of the material is relatively uniform, about 500 nm. Figure 3 The image shown is a transmission electron microscope (TEM) image of Example 1, which clearly distinguishes the structure of the material body and the coating layer. The coating layer has a uniform thickness of about 8 nm.

[0059] CoO@PBA, Ketjen Black, and PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 8:1:1 to form a slurry. This slurry was then uniformly coated onto carbon-coated aluminum foil using a 100μm doctor blade and vacuum-dried in a 120℃ vacuum oven for 12 hours. After vacuum drying, the carbon-coated aluminum foil containing the active material was cut into 11mm diameter discs and rolled, then dried in a 120℃ vacuum oven for 12 hours. After vacuum drying, the discs were weighed and transferred to a glove box for CR 2032 button cell assembly. The negative electrode used was circular sodium foil. The electrolyte solvent was a mixture of propylene carbonate (PC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) (volume ratio EC:DMC = 1:1, mass ratio (EC / DMC):FEC = 95:5), with NaClO4 as the solute and a concentration of 1 mol·L⁻¹. -1 The diaphragm is made of glass fiber (GF / F, Whatman).

[0060] Example 2

[0061] (1) Weigh 7 mmol FeSO4·7H2O, 35 mmol sodium citrate and 0.1 g ascorbic acid and dissolve them in 80 mL of deionized water to obtain solution A;

[0062] (2) Weigh 7 mmol of Na4Fe(CN)6·10H2O and dissolve it in 60 mL of deionized water to obtain solution B;

[0063] (3) Under magnetic stirring and a nitrogen atmosphere, solution A was injected into solution B using a syringe pump. The magnetic stirring speed was set to 500 rpm and the injection rate to 0.5 mL / min. -1 ;

[0064] (4) After injection, continue stirring for 2 hours, then age for 4 hours;

[0065] (5) After aging, centrifuge and wash with deionized water 3 times. The centrifugation program is 10,000 rpm for 5 minutes.

[0066] (6) The product from step (5) was placed in a vacuum oven at 120°C and vacuum dried for 12 hours to obtain Prussian blue cathode material PBA.

[0067] (7) Weigh 3.0g NaBH4 and 0.3g NaOH and dissolve them in a mixed solvent of 30mL deionized water and anhydrous ethanol (volume ratio 1:1), and denote it as solution C;

[0068] (8) Weigh 1.0g PBA and 0.05g Co(NO3)2 and disperse them in a mixed solvent of 40mL deionized water and anhydrous ethanol (volume ratio 1:1), and record it as solution D. Stir thoroughly for 1h.

[0069] (9) Under magnetic stirring, solution C was injected into solution D using a syringe pump at a rate of 0.3 mL / min. -1 ;

[0070] (10) After injection, continue stirring for 2 hours;

[0071] (11) After completion, centrifuge and wash 3 times with mixed solvent. The centrifugation program is 10,000 rpm for 5 min.

[0072] (12) The product from step (11) was placed in a vacuum oven at 120°C and dried under vacuum for 12 hours to obtain the coated Prussian blue analog material CoO / CoB@PBA.

[0073] Example 3

[0074] The preparation method of the coated Prussian blue analog material provided in this embodiment is the same as in Example 2, except that in step (8), Co(NO3)2 is replaced with Fe(NO3)3. The product obtained is FeO / FeB@PBA.

[0075] Example 4

[0076] The preparation method of the coated Prussian blue analog material provided in this embodiment is the same as in Example 2, except that in step (8), Co(NO3)2 is replaced with Ni(NO3)2. The product obtained is NiO / NiB@PBA.

[0077] Example 5

[0078] The preparation method of the coated Prussian blue analog material provided in this embodiment is the same as in Example 2, except that in step (8), Co(NO3)2 is replaced with Cu(NO3)2. The product obtained is CuO / CuB@PBA.

[0079] Comparative Example 1

[0080] (1) Weigh 7 mmol FeSO4·7H2O, 35 mmol sodium citrate and 0.1 g ascorbic acid and dissolve them in 80 mL of deionized water to obtain solution A;

[0081] (2) Weigh 7 mmol of Na4Fe(CN)6·10H2O and dissolve it in 60 mL of deionized water to obtain solution B;

[0082] (3) Under magnetic stirring and a nitrogen atmosphere, solution A was injected into solution B using a syringe pump. The magnetic stirring speed was set to 500 rpm and the injection rate to 0.5 mL / min. -1 ;

[0083] (4) After injection, continue stirring for 2 hours, then age for 4 hours;

[0084] (5) After aging, centrifuge and wash with deionized water 3 times. The centrifugation program is 10,000 rpm for 5 minutes.

[0085] (6) The product from step (5) was placed in a vacuum oven at 120°C and dried under vacuum for 12 hours to obtain Prussian blue analog material PBA.

[0086] PBA, Ketjen Black, and PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 8:1:1 to form a slurry. This slurry was then uniformly coated onto carbon-coated aluminum foil using a 100μm doctor blade and vacuum-dried in a 120℃ vacuum oven for 12 hours. After vacuum drying, the carbon-coated aluminum foil containing the active material was cut into 11mm diameter discs and rolled, then dried in a 120℃ vacuum oven for 12 hours. After vacuum drying, the discs were weighed and transferred to a glove box for CR 2032 button cell assembly. The negative electrode used was circular sodium foil. The electrolyte solvent was a mixture of propylene carbonate (PC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC) (volume ratio EC:DMC = 1:1, mass ratio (EC / DMC):FEC = 95:5), with NaClO4 as the solute and a concentration of 1 mol·L⁻¹. -1 The diaphragm is made of glass fiber (GF / F, Whatman).

[0087] from Figure 4 and Figure 5 As can be seen from the cycle performance comparison graph, compared with Comparative Example 1, the sodium-ion battery using the Prussian blue analog material CoO@PBA coated in Example 1 as the cathode material showed a significant improvement in cycle stability at both low and high current densities. At 100 mA·g -1 At the current density, the discharge specific capacity in the first week is 123.1 mAh g. -1 After 700 cycles, the capacity retention of the material in Example 1 was 80%, while that of Comparative Example 1 was only 46.4%. (At 1000 mA·g) -1 At the current density, the discharge specific capacity in the first week is 108.7 mAh g. -1 After 1600 cycles, the capacity retention rate of the material in Example 1 was 80%, while that of Comparative Example 1 was only 38.2%.

[0088] from Figure 6 It can also be seen that, compared with Comparative Example 1, the sodium-ion battery using the coated Prussian blue analog material CoO / CoB@PBA as the cathode material in Example 2 also shows a significant improvement in cycle stability.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Prussian blue analogue material, characterized in that, It consists of a Prussian blue analog matrix and its coating layer, wherein the chemical formula of the Prussian blue analog matrix is ​​A. x M A [M B (CN)6] 1-y ⋅□ y ⋅nH₂O, 0≤x≤2, 0≤y<1, n≥0, A represents alkali metal or alkaline earth metal cation, M A M B Each is independently selected from at least one of Fe, Mn, Co, Ni, Cu, and Zn, where □ represents M. B (CN)6 cavity; the coating layer is a transition metal oxide MO and a boride MB, wherein M is selected from at least one of Fe, Co, Ni and Cu.

2. The Prussian blue analogue material as described in claim 1, characterized in that, The transition metal oxide and boride used as the coating layer are selected from at least one of FeO, Fe2O3, FeB, CoO, Co2O3, CoB, NiO, NiB, CuO, and CuB.

3. The Prussian blue analogue material as described in claim 1, characterized in that, The coating layer accounts for 0.5% to 10 wt% of the total mass of the Prussian blue analog material.

4. The Prussian blue analogue material as described in claim 1, characterized in that, The Prussian blue analogue material is a face-centered cubic crystal with a particle size of 400-600 nm; the coating layer has a thickness of 5-10 nm.

5. The Prussian blue analogue material as described in claim 1, characterized in that, 1.7≤x≤2, 0≤y≤0.2, 0≤n≤3.

6. A method for preparing the Prussian blue analogue material according to any one of claims 1 to 5, comprising the following steps: 1) Preparation of Prussian blue analogues; 2) A material is prepared by reacting a Prussian blue analogue and a transition metal M salt in solution to obtain a transition metal oxide MO and a boride MB coating a Prussian blue analogue matrix.

7. The preparation method according to claim 6, characterized in that, Step 2) includes: 2a) A solution C is obtained by mixing a Prussian blue analogue and a transition metal M salt in a solvent; 2b) Dissolve sodium borohydride and sodium hydroxide in a solvent to obtain solution D; 2c) Add solution D to solution C at a certain rate and react at 0~100℃ for 0.5~24 h with stirring; 2d) After the reaction is complete, centrifuge to separate the precipitate and vacuum dry it to obtain the coated Prussian blue analog material.

8. The preparation method according to claim 7, characterized in that, In step 2a), the molar ratio of Prussian blue analogue to transition metal M salt in solution C is 1:0.01 to 1:0.2; in step 2b), the mass fraction of sodium borohydride in solution D is 1% to 20%, and the mass fraction of sodium hydroxide is 1% to 5%; the molar ratio of transition metal M salt in solution C to sodium borohydride and sodium hydroxide in solution D is 1:1 to 1:

2.

9. The preparation method according to claim 7, characterized in that, The transition metal M salt is one or more of the following: sulfate and its hydrate, nitrate and its hydrate, chloride and its hydrate, acetate and its hydrate, oxalate and its hydrate.

10. A sodium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode is made of a Prussian blue analog material as described in any one of claims 1 to 5.

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