Potassium ion battery negative electrode material and preparation method and application thereof

Abstract

The application discloses a kind of potassium ion battery negative electrode material and preparation method and application thereof, and specifically relates to the field of potassium ion battery negative electrode material.The preparation method of the potassium ion battery negative electrode material provided by the application first prepares the composite ZIF (zeolite imidazolate framework material) nanoparticles containing two elements of iron and cobalt, and then polypyrrole is used to coat the ZIF nanoparticles and carbonize the polypyrrole, to obtain ZIF nanoparticles coated with a relatively thick polypyrrole carbon coating layer, which can be used as a potassium ion battery negative electrode material.The coating layer can not only inhibit the large volume expansion of ZIF nanoparticles during the charging and discharging process of the potassium battery, but also provide a certain buffer space for the volume expansion, thereby improving the cycle stability and conductivity of the battery.

Description

Technical Field

[0001] This invention relates to the field of potassium-ion battery anode materials, specifically to a potassium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] In recent years, as lithium-ion batteries have gradually reached a bottleneck, researchers have been searching for a new rechargeable battery technology to compensate for their shortcomings. Potassium-ion batteries have become a new research hotspot in energy storage technology. The principle of potassium-ion batteries is similar to that of lithium-ion batteries, the difference being that potassium-ion batteries use potassium ions instead of lithium ions for charge transfer. Compared to lithium-ion batteries, potassium-ion batteries are simpler to design, use cheaper materials and manufacturing processes, and are rich in potassium resources with low cost. Electrode materials, as the core components of potassium-ion batteries, determine their performance; the negative electrode material plays a particularly crucial role in improving the performance of potassium-ion batteries.

[0003] Ion batteries using transition metals such as iron and cobalt as the main anode materials have advantages such as high specific capacity and environmental friendliness, making transition metals a promising anode material. However, when used as anode materials in potassium-ion batteries, transition metals exhibit very poor electron and ion conductivity. Furthermore, during charge and discharge, the electrode material undergoes significant volume changes due to ion insertion and extraction, leading to pulverization and limiting the cycle life of potassium-ion batteries. Coating anode materials with conductive polymers is a feasible approach, particularly using polypyrrole. Since polypyrrole is a p-type material, coating transition metals with polypyrrole can improve hole conductivity and enhance battery performance.

[0004] Existing technology discloses a cobalt carbonate-polypyrrole composite anode material for power lithium batteries and its preparation method. This material has a micro-nano-scale spherical core-shell structure, with a cobalt carbonate core inside and polypyrrole coating on the outside, which alleviates the battery capacity decay problem caused by severe volume swing of transition metals during charge and discharge. However, the tightly coated core-shell structure reduces the potassium storage performance of the anode when this material is used to prepare potassium-ion battery anode materials. This is because potassium ions have a large ionic radius, and during the charge and discharge process of potassium-ion batteries, potassium ions need to repeatedly insert and extract into the anode material prepared from transition metals. Therefore, a certain degree of volume expansion can facilitate the migration of potassium ions during battery charge and discharge, improving the conductivity of the anode material. However, excessive volume expansion can cause the structure of the anode material to collapse, which is detrimental to improving the cycle performance of potassium-ion batteries. Summary of the Invention

[0005] To address the problem that existing technologies cannot adequately buffer the volume expansion of potassium-ion battery anode materials, this invention provides a method for preparing potassium-ion battery anode materials. This method yields ZIF (zeolite-like imidazole ester framework material) nanoparticles with a thick polypyrrole carbon coating, which can be used as anode materials for potassium-ion batteries. The coating layer can both suppress the large volume expansion of ZIF nanoparticles during the charging and discharging process of potassium batteries and provide a certain buffer space for their volume expansion, thereby improving the cycle stability and conductivity of the battery.

[0006] Another object of the present invention is to provide a potassium-ion battery anode material prepared by the above-mentioned method for preparing potassium-ion battery anode materials.

[0007] Another object of the present invention is to provide a potassium-ion battery anode prepared from the above-mentioned potassium-ion battery anode material.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned potassium-ion battery negative electrode.

[0009] Another object of the present invention is to provide a potassium-ion battery.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution:

[0011] A method for preparing a potassium-ion battery anode material includes the following steps:

[0012] S1. Iron and cobalt salts were dissolved in an organic solvent to obtain an iron / cobalt mixed solution, and 2-substituted imidazole was added to obtain iron / cobalt composite ZIF nanoparticles;

[0013] S2. Dissolve the iron / cobalt composite ZIF nanoparticles obtained in step S1 in water, add pyrrole, and after mixing evenly, add a free radical initiator to initiate a polymerization reaction. After the reaction is completed, a potassium-ion battery anode material precursor is obtained. Calcination yields the potassium-ion battery anode material.

[0014] In step S2, the concentration of pyrrole in the aqueous solution is not less than 0.02 mol / L.

[0015] In a specific embodiment of the present invention, the iron salt and cobalt salt in step S1 can be ferric ammonium citrate and cobalt nitrate, respectively; the organic solvent can be ethanol; the 2-substituted imidazole can be 2-methylimidazolium or 2-phenylimidazolium; the free radical initiator in step S2 can be ferric chloride or ammonium persulfate; the calcination heating program can be: 5 min... -1 The heating rate was set so that the temperature was first raised from room temperature to 450℃ and held for 2 hours, then raised to 850℃ and held for 2 hours.

[0016] The purpose of step S1 is to construct iron / cobalt composite ZIF (Zeoliticimidazolate framework) nanoparticles containing both iron and cobalt. When 2-substituted imidazole is added to an iron / cobalt mixed solution, the imidazole in the 2-substituted imidazole forms an organic ligand framework around the iron and cobalt metals, forming ZIF nanoparticles that precipitate in the system.

[0017] The ZIF nanoparticles are constructed using iron and cobalt because the preparation method provided in this invention requires the ZIF nanoparticles to adsorb pyrrole monomers, thereby forming a coating layer around the ZIF nanoparticles. ZIF nanoparticles containing both iron and cobalt have pores suitable for adsorbing pyrrole monomers, which is beneficial for forming a thicker polypyrrole coating layer.

[0018] The purpose of step S2 is to form a polypyrrole carbon coating layer around the iron / cobalt composite ZIF nanoparticles. After dissolving the iron / cobalt composite ZIF nanoparticles in water, pyrrole and a free radical initiator are added, forming a polypyrrole coating layer around the ZIF nanoparticles. Upon calcination, polypyrrole carbon is formed, retaining some of the polypyrrole structure, but removing impurities such as N, H, and O (excluding carbon). The reason for forming polypyrrole carbon is that while polypyrrole itself is a conductive polymer, its internal structure is relatively compact, which is not conducive to providing buffer space for the volume expansion of transition metals during the charging and discharging process of potassium-ion batteries. After calcination to form polypyrrole carbon, the framework structure of polypyrrole itself is preserved, but because impurities such as N, H, and O are removed, certain voids are formed in the polypyrrole carbon coating layer. These voids provide buffer space for the volume expansion of the transition metals, while also inhibiting the expansion to a certain extent, preventing excessive expansion that could lead to the collapse of the ZIF nanoparticle structure.

[0019] Limiting the concentration of pyrrole in the aqueous solution to above 0.02 mol / L is to control the thickness of the polypyrrole carbon coating layer formed around the ZIF nanoparticles. When the concentration of pyrrole in the aqueous solution is not less than 0.02 mol / L, the thickness of the polypyrrole coating layer around the iron / cobalt composite ZIF nanoparticles can reach more than 225 times the particle size of the ZIF nanoparticles. The volume of the polypyrrole carbon coating layer formed by calcining polypyrrole shrinks by about 40% compared to the polypyrrole coating layer. Therefore, the final particle size of the polypyrrole carbon particles is more than 90 times the particle size of the ZIF nanoparticles, i.e., the particle size D of the iron / cobalt composite ZIF nanoparticles is... 50 The particle size D of polypyrrole carbon particles 50The thickness is 10% or even lower. The reason such a thick coating layer can be formed is that the iron / cobalt composite ZIF nanoparticles provided by this invention can capture pyrrole monomers through their own pores, increasing the number of pyrrole monomers surrounding the ZIF nanoparticles. Then, the pyrrole monomers rapidly polymerize under the action of a free radical initiator, forming a polypyrrole coating layer. It should be noted that the polypyrrole carbon coating layer and the iron / cobalt composite metal nanoparticles do not form a strict "core-shell structure." The distribution of the iron / cobalt composite metal nanoparticles in the polypyrrole carbon coating material, which is many times larger than its own volume, is approximately random.

[0020] The negative electrode material provided by this invention primarily utilizes metal to provide sites for potassium ion insertion and extraction during the charging and discharging process of potassium-ion batteries. However, metal is prone to volume expansion and structural collapse during potassium ion insertion and extraction. To address this issue, a coating layer needs to be prepared around the iron / cobalt composite ZIF nanoparticles to suppress volume expansion. However, due to the presence of numerous voids in the coating layer, when the coating layer thickness is too low, the voids make it difficult to effectively suppress excessive volume expansion of the metal material during potassium-ion battery charging and discharging. With a thicker coating layer, even with voids within the coating layer, excessive volume expansion can be suppressed. Furthermore, the voids within the coating layer provide a buffer space for volume expansion, allowing the potassium-ion battery negative electrode material to undergo controllable volume expansion within a limited space, thus promoting potassium ion insertion and extraction. Simultaneously, polypyrrole carbon can also provide certain potassium insertion sites.

[0021] Preferably, the concentration of pyrrole in the aqueous solution in step S2 is 0.02 to 0.06 mol / L.

[0022] When the concentration of pyrrole in the aqueous solution continues to increase to above 0.06 mol / L, the thickness of the polypyrrole carbon coating layer becomes difficult to further increase. Therefore, the thickness of the polypyrrole carbon coating layer in the potassium-ion battery anode material obtained by the preparation method provided in this invention can only reach the particle size D of the iron / cobalt composite ZIF nanoparticles. 50 99 times.

[0023] Preferably, the molar ratio of iron salt to cobalt salt in step S1 is 1:(1 to 2.5).

[0024] The optimal molar ratio of iron and cobalt salts is chosen to allow iron and cobalt in ZIF nanoparticles to complement each other. Given that iron and cobalt can recombine to form ZIF nanoparticles with pores suitable for pyrrole adsorption, controlling the ratio of iron to cobalt salts yields anode materials with better cycle stability and conductivity. When there is more iron in the ZIF nanoparticles, the resulting anode material has poorer conductivity; when there is more cobalt, the resulting anode material has poorer cycle stability.

[0025] Preferably, the free radical initiator in step S2 is ammonium persulfate.

[0026] Using ammonium persulfate as an initiator can yield anode materials with higher conductivity and better cycle performance.

[0027] Preferably, the polymerization reaction time in step S2 is 2 to 5 hours.

[0028] This invention also protects a potassium-ion battery anode material prepared using the above-described method for preparing potassium-ion battery anode materials.

[0029] The potassium-ion battery anode material provided by this invention has a structure formed by the stacking of polypyrrole carbon spherical particles. Iron / cobalt composite ZIF nanoparticles are dispersed within the polypyrrole carbon spherical particles, and the particle size D of the iron / cobalt composite ZIF nanoparticles is... 50 The particle size D of polypyrrole carbon spherical particles 50 1% to 10%.

[0030] This invention also protects a potassium-ion battery anode prepared using the above-mentioned potassium-ion battery anode material.

[0031] This invention also protects a method for preparing the above-mentioned potassium-ion battery negative electrode, comprising the following steps:

[0032] The potassium-ion battery anode material, conductive agent and binder are thoroughly mixed, and a surfactant is added and then thoroughly mixed to obtain a slurry. The slurry is then coated onto a current collector to obtain the potassium-ion battery anode.

[0033] In a specific embodiment of the present invention, the conductive agent may be acetylene black, and the binder may be polyvinylidene fluoride (PVDF).

[0034] Preferably, the mass ratio of potassium-ion battery negative electrode material, conductive agent and binder is 7:(1-2):(1-2).

[0035] This invention also protects a potassium-ion battery, the negative electrode of which is the negative electrode of the aforementioned potassium-ion battery.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The potassium-ion battery anode prepared using the method provided in this invention exhibits excellent cycle performance and conductivity. Cycle performance is characterized by capacity retention at 100 mA g / g. -1After 100 cycles of charge and discharge at the specified current, the potassium-ion battery prepared using the negative electrode material combination of the present invention still has a capacity retention rate of up to 59.97%, and the charge transfer impedance of the battery can reach as low as 146Ω, indicating excellent conductivity. Attached Figure Description

[0038] Figure 1 This is a SEM image of the potassium-ion battery anode material prepared in Example 1 of the present invention.

[0039] Figure 2 This is a TEM image of the potassium-ion battery anode material prepared in Example 1 of the present invention at a scale of 200 nm.

[0040] Figure 3 This is a TEM image of the potassium-ion battery anode material prepared in Example 1 of the present invention at the 10 nm scale.

[0041] Figure 4 EDX spectrum of the potassium-ion battery anode material prepared in Example 1 of this invention.

[0042] Figure 5 The diagram shows the cycle performance of a potassium-ion battery prepared using the potassium-ion battery anode material prepared in Example 1 of this invention. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0044] Example 1

[0045] A method for preparing a potassium-ion battery anode material includes the following steps:

[0046] S1. Iron / cobalt mixed solution was obtained by dissolving ferric ammonium citrate and cobalt nitrate in ethanol, with a molar ratio of ferric ammonium citrate to cobalt nitrate of 1:1.7. 2-methylimidazole was added to obtain iron / cobalt composite ZIF nanoparticles.

[0047] S2. Dissolve the iron / cobalt composite ZIF nanoparticles obtained in step S1 in water, add pyrrole, and after mixing evenly, add ammonium persulfate to initiate a polymerization reaction. The polymerization reaction time is 3 hours. After the reaction is completed, a potassium-ion battery anode material precursor is obtained. Calcination yields the potassium-ion battery anode material.

[0048] In step S2, the concentration of pyrrole in the aqueous solution is 0.043 mol / L.

[0049] Example 2

[0050] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0051] In step S2, the concentration of pyrrole in the aqueous solution is 0.02 mol / L.

[0052] Example 3

[0053] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0054] In step S2, the concentration of pyrrole in the aqueous solution is 0.06 mol / L.

[0055] Example 4

[0056] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0057] In step S1, the molar ratio of ferric ammonium citrate to cobalt nitrate is 1:1.

[0058] Example 5

[0059] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0060] In step S1, the molar ratio of ferric ammonium citrate to cobalt nitrate is 1:2.5.

[0061] Example 6

[0062] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0063] In step S1, the molar ratio of ferric ammonium citrate to cobalt nitrate is 1:0.5.

[0064] Example 7

[0065] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0066] In step S1, the molar ratio of ferric ammonium citrate to cobalt nitrate is 1:4.

[0067] Example 8

[0068] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0069] In step S2, the initiator is ferric chloride.

[0070] Comparative Example 1

[0071] A method for preparing a potassium-ion battery anode material is carried out using the method disclosed in Example 1 of Chinese Patent CN104157838A.

[0072] Comparative Example 2

[0073] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0074] In step S2, the concentration of pyrrole in the aqueous solution is 0.01 mol / L.

[0075] Comparative Example 3

[0076] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0077] In step S1, ferric ammonium citrate and nickel nitrate are dissolved in an organic solvent.

[0078] Comparative Example 4

[0079] A method for preparing a potassium-ion battery anode material differs from Example 1 in that:

[0080] In step S1, nickel nitrate and cobalt nitrate are dissolved in an organic solvent.

[0081] Performance testing

[0082] Battery assembly: The potassium-ion battery anode material, conductive agent acetylene black, and binder PVDF obtained in the examples and comparative examples are thoroughly mixed. N-methylpyrrolidone is added and then thoroughly mixed to obtain a slurry. The slurry is coated on the current collector copper foil and dried at 60°C for 12 hours to obtain the potassium-ion battery anode. Button cells are assembled in an argon-filled glove box, using potassium foil as the counter electrode, glass microfiber as the separator, and KPF6 as the electrolyte to obtain the potassium-ion battery.

[0083] Cycle performance testing: The potassium-ion battery was tested using the LAND series battery testing system, with the battery operating at 100 mA g. -1 The specific capacity of the battery after 100 cycles of charge and discharge at the specified current is divided by the specific capacity of the first discharge cycle to obtain the specific capacity retention rate of the battery after 100 cycles. This specific capacity retention rate characterizes the cycle performance of the battery.

[0084] Conductivity test: Electrochemical impedance spectroscopy (EIS) was performed on the battery using a CHI600E electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.). The test temperature was 25℃, the frequency was 10mHz~100kHz, and the AC voltage amplitude was 5mV. The charge transfer impedance R was obtained from the test. ct , with R ct R characterizes the conductivity of a battery. ct The lower the conductivity, the better.

[0085] Performance test data are shown in Table 1 below. Figures 1-4 As shown:

[0086] Table 1. Data from Examples and Comparative Examples

[0087]

[0088]

[0089] As can be seen from the data in Examples 1-3 of Table 1, when the concentration of pyrrole in the aqueous solution in step S2 is 0.02-0.06 mol / L, the potassium-ion batteries prepared using the negative electrode material prepared according to the present invention all exhibit excellent cycle performance and good conductivity. As can be seen from the data in Examples 4-7, when the molar ratio of iron salt to cobalt salt in step S1 is the preferred ratio of 1:(1-2.5) of the present invention (Examples 4-5), the potassium-ion battery exhibits even better cycle performance. However, when the amount of iron salt is too small, the conductivity of the potassium-ion battery is poor, and when the amount of cobalt salt is too large, the cycle performance of the battery decreases. As can be seen from the data in Example 8, when the free radical initiator is ammonium persulfate, the battery exhibits better cycle performance and conductivity. This is because using ammonium persulfate as an initiator can yield a negative electrode material with higher conductivity and better cycle performance. As can be seen from the data in Comparative Example 1, the present invention represents a significant improvement over the prior art. According to Comparative Example 2, in the preparation method provided by this invention, the concentration of pyrrole in the aqueous solution in step S2 must be no less than 0.02 mol / L; otherwise, it is difficult to form a coating layer with sufficient thickness. Data from Comparative Examples 3 and 4 show that only composite ZIF nanoparticles formed from iron and cobalt can possess pores suitable for pyrrole polymerization, thus resulting in better cycle performance and conductivity of the battery.

[0090] Figure 1 This is a SEM image of the potassium-ion battery anode material prepared in Example 1 of the present invention. Figure 1 As can be seen from the above, the potassium-ion battery anode material provided by this invention is in granular form.

[0091] Figure 2 This is a TEM image of the potassium-ion battery anode material prepared in Example 1 of this invention at a scale of 200 nm. Figure 3 This is a TEM image of the potassium-ion battery anode material prepared in Example 1 of this invention at a 10 nm scale. From... Figures 2-3 As can be seen from the above, the potassium-ion battery anode material provided by this invention has a structure of polypyrrole carbon-coated iron / cobalt composite metal nanoparticles, and according to instrumental calculations, the particle size D of the polypyrrole carbon particles is... 50 It is approximately 100 nm in size, while the particle size D of the ZIF nanoparticles is... 50Approximately 6 nm, the thickness of the polypyrrole carbon coating is more than 90 times the particle size of the ZIF nanoparticles, meaning the particle size D of the iron / cobalt composite ZIF nanoparticles is... 50 The particle size D of polypyrrole carbon particles 50 The content is 10% or even lower, and the distribution of composite metal nanoparticles in the polypyrrole carbon layer is approximately random. TEM images of the potassium-ion battery anode materials prepared in Examples 2-8 are similar to those in Example 1.

[0092] Figure 4 This is the EDX spectrum of the potassium-ion battery anode material prepared in Example 1 of this invention. Figure 4 It can be confirmed that the potassium-ion battery anode material provided by the present invention contains two metals, iron and cobalt.

[0093] Figure 5 This is a cycle performance diagram of a potassium-ion battery prepared using the potassium-ion battery anode material prepared in Example 1 of this invention. From... Figure 5 As can be seen from the above, the potassium-ion battery prepared using the potassium-ion battery anode material provided by the present invention has excellent cycle performance.

[0094] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a potassium-ion battery anode material, characterized in that, Includes the following steps: S1. Iron and cobalt salts were dissolved in an organic solvent to obtain an iron / cobalt mixed solution, and 2-substituted imidazole was added to obtain iron / cobalt composite ZIF nanoparticles; S2. Dissolve the iron / cobalt composite ZIF nanoparticles obtained in step S1 in water, add pyrrole, and after mixing evenly, add a free radical initiator to initiate a polymerization reaction. After the reaction is completed, a potassium-ion battery anode material precursor is obtained. Calcination yields the potassium-ion battery anode material. In step S2, the concentration of pyrrole in the aqueous solution is not less than 0.02 mol / L; The structure of the potassium-ion battery anode material is formed by the stacking of polypyrrole carbon spherical particles. Iron / cobalt composite ZIF nanoparticles are dispersed within the polypyrrole carbon spherical particles, and the particle size D of the iron / cobalt composite ZIF nanoparticles is... 50 The particle size D of polypyrrole carbon spherical particles 50 1% to 10%.

2. The method for preparing the potassium-ion battery anode material as described in claim 1, characterized in that, In step S2, the concentration of pyrrole in the aqueous solution is 0.02~0.06 mol / L.

3. The method for preparing the potassium-ion battery anode material as described in claim 1, characterized in that, In step S1, the molar ratio of iron salt to cobalt salt is 1:(1~2.5).

4. The method for preparing the potassium-ion battery anode material as described in claim 1, characterized in that, In step S2, the free radical initiator is ammonium persulfate.

5. The method for preparing the potassium-ion battery anode material as described in claim 1, characterized in that, The polymerization reaction in step S2 takes 2 to 5 hours.

6. A potassium-ion battery anode material prepared by the method for preparing potassium-ion battery anode material according to any one of claims 1 to 5.

7. A potassium-ion battery anode prepared using the potassium-ion battery anode material as described in claim 6.

8. A method for preparing the potassium-ion battery negative electrode according to claim 7, characterized in that, Includes the following steps: The potassium-ion battery anode material, conductive agent and binder are thoroughly mixed, and a surfactant is added and then thoroughly mixed to obtain a slurry. The slurry is then coated onto a current collector to obtain the potassium-ion battery anode.

9. The method for preparing the potassium-ion battery negative electrode as described in claim 8, characterized in that, The mass ratio of potassium-ion battery anode material, conductive agent and binder is 7:(1~2):(1~2).

10. A potassium-ion battery, characterized in that, The negative electrode of the potassium-ion battery is the negative electrode of the potassium-ion battery according to claim 7.

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