Preparation method of three-dimensional porous negative electrode material for ultra-low temperature lithium iron phosphate battery

Abstract

This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries. The method includes adding an ionic liquid modifier A, graphene oxide, and an organic solvent to a reactor, then adding porous silicon PSi to obtain a PSi@GO precursor; heating the PSi@GO precursor to 600-900℃ under an argon atmosphere to obtain the three-dimensional porous anode material; the three-dimensional porous anode material prepared using this invention enables lithium iron phosphate batteries to exhibit excellent cycle stability at both room temperature and low temperatures.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing a three-dimensional porous negative electrode material for ultra-low temperature lithium iron phosphate batteries. Background Technology

[0002] Lithium-ion batteries, or "lithium batteries" for short, are mainly composed of five parts: positive and negative electrodes, a separator, an electrolyte, and a battery casing. The materials for the positive and negative electrodes are currently a major research focus. As the most important part of a lithium battery, they are the main substances and carriers for the battery reaction, determining characteristics such as battery capacity, cycle life, and energy density. Generally, the positive electrode material provides the lithium metal source for the lithium-ion battery and is mainly composed of active materials, binders, and conductive agents. Part of this lithium metal source contributes lithium ions during the charge-discharge cycle, and another part is used to form the solid electrolyte interphase (SEI) film, consuming lithium. Currently, the lithium battery positive electrode materials on the market are mainly lithium intercalation compounds formed by transition metal elements and lithium elements, classified by structure as: cubic spinel structure (LiMn2O4), orthorhombic olivine structure (LiFePO4), and hexagonal layered structure (LiCoO2). Among them, lithium iron phosphate (LiFePO4) is a common type of lithium intercalation compound. Due to its advantages such as high safety, long cycle life, environmental friendliness, and relatively low cost, lithium iron phosphate (LFP) batteries have become one of the mainstream technologies for power and energy storage batteries. However, traditional LFP batteries generally suffer from a sharp decline in performance when exposed to ultra-low temperature environments, which severely restricts their application in cold regions.

[0003] Many factors limit the ultra-low temperature performance of lithium iron phosphate (LFP) batteries, involving multiple components such as cathode materials, anode materials, and electrolytes. Among them, the kinetic lag of anode materials at low temperatures is considered one of the core bottlenecks. To improve the low-temperature performance of LFP batteries, researchers currently focus on electrolyte optimization (such as developing electrolyte formulations with low freezing points and high conductivity, and introducing film-forming additives), cathode material modification (such as nano-sizing and carbon coating to improve conductivity), and anode material innovation. Regarding anode materials, three-dimensional porous electrode structures are considered an effective way to improve low-temperature performance, mainly because: 1) well-developed pore structures (including micropores, mesopores, and macropores) can fully wet the electrolyte, providing a "highway" for ion transport, effectively shortening the ion diffusion path, and alleviating the problems of difficult electrolyte penetration and slow ion transport at low temperatures; 2) high specific surface area helps increase the electrode / electrolyte contact interface, reducing local current density and thus reducing charge transfer impedance; 3) porous structures can buffer volume changes during lithium-ion insertion / extraction, improving structural stability.

[0004] However, silicon exhibits poor conductivity and a high volume expansion rate (approximately 300%) during charge-discharge cycles, making silicon electrodes prone to pulverization and resulting in an unstable solid electrolyte interphase (SEI) film, leading to a rapid decrease in specific capacity during cycling. Combining silicon with carbon materials is a crucial strategy for addressing the conductivity and volume expansion issues of silicon anode materials. Commonly used carbon materials include graphite, graphene, and carbon nanotubes.

[0005] In summary, developing a method that is simple, highly controllable, cost-effective, and capable of mass-producing high-performance three-dimensional porous anode materials suitable for ultra-low temperature lithium iron phosphate batteries is of great scientific significance for overcoming the bottleneck of low-temperature applications of lithium iron phosphate batteries, expanding their application scenarios, and promoting the popularization of new energy technologies under a wider range of climatic conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries, thereby solving the problem of poor cycle stability of existing lithium iron phosphate batteries at low temperatures. To address the above technical problems, this invention provides the following technical solution:

[0007] A method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries includes the following steps:

[0008] Step 1: Preparation of porous silicon PSi

[0009] Si / Al alloy powder was added to an acidic solution for reaction, filtered, and the filter cake was washed with deionized water until the pH of the filtrate was neutral. Then the filter cake was dried to obtain porous silicon PSi.

[0010] Step 2: Preparation of three-dimensional porous anode materials

[0011] Ionic liquid modifier A, graphene oxide, and organic solvent were added to a reactor and ultrasonically stirred for 1-5 hours. Then, porous silicon PSi was added, and the mixture was stirred ultrasonically for another 1-3 hours. The mixture was then dried in a freeze dryer to obtain the PSi@GO precursor. The dried PSi@GO precursor was heated to 600-900℃ and held for 1-5 hours under an argon atmosphere, and then cooled to room temperature to obtain a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries.

[0012] The structural formula of the ionic liquid modifier A is:

[0013] .

[0014] In some embodiments, in step 1, the acidic solution is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

[0015] In some embodiments, in step 1, the Si content in the Si / Al alloy powder is 10~30wt%; and the concentration of the acidic solution is 1~3mol / L.

[0016] In some embodiments, in step 2, the mass ratio of the ionic liquid modifier A to graphene oxide is 1:(1.0~2.0); the mass ratio of the ionic liquid modifier A to porous silicon PSi is 1:(5.0~10.0).

[0017] In some embodiments, in step 2, the organic solvent is selected from one or more of ethanol, methanol, isopropanol, tetrahydrofuran, DMSO, and DMF.

[0018] In some implementations, in step 2, the temperature of ultrasonic stirring is 50~90℃; the heating rate is 3~10℃ / min.

[0019] In some embodiments, step 2, the method for preparing the graphene oxide includes the following steps:

[0020] Raw graphite powder and concentrated sulfuric acid were added to a reactor, and KMnO4 was added under ice bath conditions and stirred until homogeneous. Then, deionized water and H2O2 solution were added sequentially until the mixture changed from purple to yellow and was allowed to stand. Then, HCl was added, and the mixture was ultrasonically stirred until homogeneous. After centrifugation, the product was washed with deionized water until neutral and then vacuum dried to obtain graphene oxide.

[0021] This invention also protects the three-dimensional porous anode material prepared by the above method.

[0022] This invention also protects an ultra-low temperature lithium iron phosphate battery, which includes the above-mentioned three-dimensional porous negative electrode material.

[0023] The present invention has achieved the following beneficial effects:

[0024] 1) The three-dimensional porous anode material prepared by the present invention enables lithium iron phosphate batteries to exhibit excellent cycle stability at both room temperature and low temperature.

[0025] 2) The two imidazole rings in ionic liquid modifier A are both electron-rich systems and positively charged. They can combine with graphene oxide through "cation-π" and "π-π stacking" mechanisms. The modified graphene oxide greatly reduces agglomeration, allowing it to be uniformly dispersed in porous silicon PSi. Adding graphene oxide with a certain degree of toughness to the surface of porous silicon PSi helps to suppress the volume expansion of silicon, greatly eliminates the mechanical strain of the electrode material during charge-discharge cycles, and effectively improves the electrochemical performance of lithium iron phosphate batteries.

[0026] 3) The incorporation of N and Sn in ionic liquid modifier A can improve the conductivity and lithium storage active sites of the negative electrode material, thereby effectively improving the cycle performance of lithium iron phosphate batteries. Attached Figure Description

[0027] Figure 1 The image shows the 1H NMR spectrum of ionic liquid modifier A. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The endpoints and any values ​​of the ranges described in this invention 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. The raw materials and reagents used in the following examples are commercially available.

[0030] Preparation Example 1: Preparation of Ionic Liquid Modifier A

[0031]

[0032] Step S1: Under nitrogen protection, N , N '-Carbonyldiimidazole (0.2 mol), acetonitrile (150 mL), and ethanol (20 mL) were added to a reactor, followed by the slow addition of 1-chlorobutane (0.4 mol). The mixture was heated to 60 °C and stirred for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and petroleum ether (300 mL) and ethyl acetate (100 mL) were added to the reaction mixture. A brown viscous liquid was produced. The brown liquid layer was separated using a separatory funnel, and the organic solvent was removed by rotary evaporation. The concentrated solution was dried under vacuum at 100 °C for 12 h to obtain intermediate X, with a yield of 35.1%.

[0033] Step S2: Under nitrogen protection, intermediate X (0.2 mol) and water (50 mL) prepared in step S1 were added to the reactor, followed by SnCl4·5H2O (0.4 mol). The mixture was heated to 80 °C and stirred for 10 h. After the reaction was complete, the water was removed by rotary evaporation, and the mixture was dried under vacuum at 100 °C for 24 h to obtain ionic liquid modifier A, with a yield of 93.9%.

[0034] 1 H NMR (400 MHz, DMSO- d 6) δ 7.60 (s, 2H), 7.17 (s, 2H), 6.91 (s, 2H), 3.97-3.89 (m, 4H), 1.67-1.58 (m, 4H), 1.24-1.16 (m, 4H), 0.93-0.81 (m, 6H).

[0035] Preparation Example 2: Preparation of Graphene Oxide

[0036] Raw graphite powder (25.0 g) and concentrated sulfuric acid (98% by mass, 400 mL) were added to a reactor. KMnO4 (25.0 g) was added under ice bath conditions and stirred for 45 min. Then, deionized water (500 mL) and 30% H2O2 solution (100 mL) were added sequentially until the mixture changed from purple to yellow, and then allowed to stand for 24 h. Then, 10% HCl (250 mL) was added and ultrasonically stirred for 2 h. After centrifugation, the product was washed with deionized water until neutral, and then vacuum dried at 120 °C to obtain graphene oxide.

[0037] Example 1

[0038] A method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries includes the following steps:

[0039] Step 1: Preparation of porous silicon PSi

[0040] 10g of Si / Al alloy powder (Si content 20wt%) was weighed and placed in 100mL of 1mol / L sulfuric acid solution. The mixture was stirred at room temperature for 12h. After the reaction was complete, the mixture was filtered and the filter cake was washed several times with deionized water until the pH of the filtrate was neutral. The filter cake was then dried in a 60℃ forced-air drying oven for 24h to obtain porous silicon PSi.

[0041] Step 2: Preparation of three-dimensional porous anode materials

[0042] The ionic liquid modifier A (10.0 g) obtained in Preparation Example 1, the graphene oxide (10.0 g) obtained in Preparation Example 2, and ethanol (200 mL) were added to the reactor and ultrasonically stirred at 60 °C for 2 h. Then, porous silicon PSi (60.0 g) was added, and the mixture was stirred ultrasonically for another 1 h. The mixture was then dried in a freeze dryer to obtain the PSi@GO precursor.

[0043] The dried PSi@GO precursor was heated to 800℃ at a heating rate of 5℃ / min under the protection of argon atmosphere and held at the temperature for 2h. Then it was naturally cooled to room temperature to obtain a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries.

[0044] Example 2

[0045] A method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries includes the following steps:

[0046] Step 1: Preparation of porous silicon PSi

[0047] 10g of Si / Al alloy powder (Si content 25wt%) was weighed and placed in 1mol / L hydrochloric acid solution (100mL), and stirred at room temperature for 10h. After the reaction was completed, the sample was filtered and washed with deionized water several times until the pH of the filtrate was neutral. Then the filter cake was dried in a 60℃ forced-air drying oven for 24h to obtain porous silicon PSi.

[0048] Step 2: Preparation of three-dimensional porous anode materials

[0049] The ionic liquid modifier A (8.0 g) obtained in Preparation Example 1, the graphene oxide (10.0 g) obtained in Preparation Example 2, and DMSO (200 mL) were added to the reactor and ultrasonically stirred at 70 °C for 1 h. Then, porous silicon PSi (60.0 g) was added, and the mixture was stirred ultrasonically for another 1 h. The mixture was then dried in a freeze dryer to obtain the PSi@GO precursor.

[0050] The dried PSi@GO precursor was heated to 800℃ at a heating rate of 5℃ / min under the protection of argon atmosphere and held at the temperature for 2h. Then it was naturally cooled to room temperature to obtain a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries.

[0051] Example 3

[0052] A method for preparing a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries includes the following steps:

[0053] Step 1: Preparation of porous silicon PSi

[0054] 10g of Si / Al alloy powder (Si content 20wt%) was weighed and placed in 100mL of 1mol / L sulfuric acid solution. The mixture was stirred at room temperature for 12h. After the reaction was complete, the mixture was filtered and the filter cake was washed several times with deionized water until the pH of the filtrate was neutral. The filter cake was then dried in a 60℃ forced-air drying oven for 24h to obtain porous silicon PSi.

[0055] Step 2: Preparation of three-dimensional porous anode materials

[0056] The ionic liquid modifier A (6.0 g) obtained in Preparation Example 1, the graphene oxide (10.0 g) obtained in Preparation Example 2, and DMSO (200 mL) were added to the reactor and ultrasonically stirred at 80 °C for 1.5 h. Then, porous silicon PSi (60.0 g) was added, and the mixture was stirred ultrasonically for another 1 h. The mixture was then dried in a freeze dryer to obtain the PSi@GO precursor.

[0057] The dried PSi@GO precursor was heated to 800℃ at a heating rate of 10℃ / min under the protection of argon atmosphere and held at the temperature for 3h. Then it was naturally cooled to room temperature to obtain a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries.

[0058] Comparative Example 1

[0059] Based on Example 1, the ionic liquid modifier A was replaced with:

[0060] Other operations and conditions are the same as in Example 1.

[0061] Comparative Example 2

[0062] Based on Example 1, the ionic liquid modifier A was replaced with 1-butyl-3-methylimidazolium hydrochloride, a common ionic liquid in the art. Other operations and conditions are the same as in Example 1.

[0063] Performance testing

[0064] The battery cycle performance of the three-dimensional porous anode materials prepared in Examples 1-3 and Comparative Examples 1-2 was tested using the following methods:

[0065] Preparation of ultra-low temperature lithium iron phosphate batteries:

[0066] Lithium iron phosphate cathode material, conductive carbon black, polyvinylidene fluoride and N-methylpyrrolidone were mixed in a mass ratio of 8:1:1:2 and ground in an agate mortar for 30 minutes to obtain a well mixed slurry. The slurry was then evenly coated onto aluminum foil using a scraper and dried in a vacuum oven at 60°C for 24 hours. Subsequently, it was punched into a disc with a diameter of 12 mm to obtain a cathode sheet with a thickness of 1 cm.

[0067] Three-dimensional porous negative electrode material, conductive carbon black, polyvinylidene fluoride and N-methylpyrrolidone were mixed in a mass ratio of 8:1:1:2 and ground in an agate mortar for 30 minutes to obtain a well mixed slurry. The slurry was evenly coated on copper foil with a scraper and dried in a vacuum oven at 60°C for 24 hours. Then it was punched into a disc with a diameter of 12 mm to obtain a negative electrode sheet with a thickness of 1 cm.

[0068] In a glove box protected by an argon atmosphere, the separator is Clegrad 2400, and the electrolyte is a 1 mol / L lithium hexafluorophosphate solution, wherein the solvent is a mixed solution of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:1:1. The above-mentioned positive electrode, electrolyte, separator, and negative electrode are stacked in sequence and formed into an electrode assembly through a winding process. The electrode assembly is then placed in an aluminum shell and sealed. Finally, after standing, formation, and shaping processes, an ultra-low temperature lithium iron phosphate battery is obtained.

[0069] 1) Room temperature cycling performance test:

[0070] At 25°C, the lithium iron phosphate battery was charged to 4.5V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C, and then discharged to 3.0V at a constant current of 0.1C. This cycle was repeated, and the capacity retention rate at the 200th cycle was calculated after 200 charge-discharge cycles.

[0071] 2) Low-temperature cycling performance test:

[0072] At -30℃, the lithium iron phosphate battery was charged to 4.5V at a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C, and then discharged to 3.0V at a constant current of 0.1C. This cycle was repeated, and the capacity retention rate at the 200th cycle was calculated after 200 charge-discharge cycles.

[0073] The test results are shown in Table 1.

[0074] Table 1 Cyclic performance test results

[0075]

[0076] As shown in Table 1, the three-dimensional porous anode material prepared using this invention enables lithium iron phosphate batteries to exhibit excellent cycle stability at both room temperature and low temperature. The main reasons are: 1) The two imidazole rings in the ionic liquid modifier A are both electron-rich systems and positively charged, allowing them to combine with graphene oxide simultaneously through "cation-π" and "π-π stacking" mechanisms. The modified graphene oxide significantly reduces agglomeration, allowing it to disperse uniformly in porous silicon PSi. Adding graphene oxide with a certain degree of toughness to the porous silicon PSi surface helps suppress silicon volume expansion, greatly eliminating mechanical strain in the electrode material during charge-discharge cycles and effectively improving the electrochemical performance of the lithium iron phosphate battery. 2) The incorporation of N and Sn in the ionic liquid modifier A can improve the conductivity and lithium storage active sites of the anode material, thereby effectively improving the cycle performance of the lithium iron phosphate battery.

[0077] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a three-dimensional porous negative electrode material for an ultra-low temperature lithium iron phosphate battery, characterized in that, Includes the following steps: Step 1: Preparation of porous silicon PSi Si / Al alloy powder was added to an acidic solution for reaction, filtered, and the filter cake was washed with deionized water until the pH of the filtrate was neutral. Then the filter cake was dried to obtain porous silicon PSi. Step 2: Preparation of three-dimensional porous anode materials Ionic liquid modifier A, graphene oxide, and organic solvent were added to a reactor and ultrasonically stirred for 1-5 hours. Then, porous silicon PSi was added, and the mixture was stirred ultrasonically for another 1-3 hours. The mixture was then dried in a freeze dryer to obtain the PSi@GO precursor. The dried PSi@GO precursor was heated to 600-900℃ and held for 1-5 hours under an argon atmosphere, and then cooled to room temperature to obtain a three-dimensional porous anode material for ultra-low temperature lithium iron phosphate batteries. The structural formula of the ionic liquid modifier A is: ; In step 2, the mass ratio of the ionic liquid modifier A to graphene oxide is 1:(1.0~2.0); the mass ratio of the ionic liquid modifier A to porous silicon PSi is 1:(5.0~10.0).

2. The production method according to claim 1, characterized by, In step 1, the acidic solution is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

3. The preparation method according to claim 1, characterized in that, In step 1, the Si content in the Si / Al alloy powder is 10~30wt%; the concentration of the acidic solution is 1~3mol / L.

4. The preparation method according to claim 1, characterized in that, In step 2, the organic solvent is selected from one or more of ethanol, methanol, isopropanol, tetrahydrofuran, DMSO and DMF.

5. The preparation method according to claim 1, characterized in that, In step 2, the temperature of ultrasonic stirring is 50~90℃; the heating rate is 3~10℃ / min.

6. The preparation method according to claim 1, characterized in that, In step 2, the method for preparing the graphene oxide includes the following steps: Raw graphite powder and concentrated sulfuric acid were added to a reactor, and KMnO4 was added under ice bath conditions and stirred until homogeneous. Then, deionized water and H2O2 solution were added sequentially until the mixture changed from purple to yellow and was allowed to stand. Then, HCl was added, and the mixture was ultrasonically stirred until homogeneous. After centrifugation, the product was washed with deionized water until neutral and then vacuum dried to obtain graphene oxide.

7. A three-dimensional porous anode material, characterized in that, It is prepared by any one of the methods of claims 1-6.

8. An ultra-low temperature lithium iron phosphate battery, characterized in that, The ultra-low temperature lithium iron phosphate battery includes the three-dimensional porous negative electrode material as described in claim 7.

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