Starch-based hard carbon material, preparation thereof and use thereof in sodium-ion batteries

Abstract

This invention belongs to the field of battery materials, specifically relating to a method for preparing a starch-based hard carbon material. The method involves first subjecting an aqueous solution containing starch raw materials to a first-stage atmospheric pressure heat treatment, followed by a second-stage high-pressure heat treatment in a sealed container, after which material A is separated. Material A and an additive are then modified by water slurry to obtain material B. The additive is an alkaline or acidic component. Material B is then carbonized at a low temperature of 750℃ to 950℃ to obtain the starch-based hard carbon material. This invention also includes the material prepared by the above method and its application in sodium batteries. This invention innovatively uses the two-stage atmospheric pressure-high pressure heat treatment of starch raw materials, combined with subsequent additive modification and low-temperature carbonization, to achieve the preparation of starch-based hard carbon at low temperatures. Furthermore, it optimizes its physicochemical structure, improving its capacity, tap density, fast charging performance, and high-rate stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage battery materials, and more particularly to a negative electrode carbon material for sodium-ion batteries and its preparation method. Background Technology

[0002] With the continuous depletion of non-renewable energy sources, developing and utilizing clean and renewable energy is an effective way to achieve energy structure transformation. However, due to the random and fluctuating characteristics of renewable energy sources such as wind and solar power, energy storage devices are required in practical applications to overcome the temporal limitations of renewable energy. Lithium-ion batteries are currently the most widely used electrochemical energy storage devices. However, due to the low abundance and uneven geographical distribution of lithium in the Earth's crust, limited lithium resources cannot meet the rapidly growing market demand for lithium-ion batteries. Sodium-ion batteries, on the other hand, have become an excellent alternative to lithium-ion batteries due to their similar physicochemical properties, lower cost, and higher safety.

[0003] In sodium-ion batteries, carbon anode materials are among the most widely studied and promising anode materials, with hard carbon materials attracting particular attention. Hard carbon is a carbon material that is difficult to graphitize even at high temperatures. Its structure can be represented by the classic "House of Cards" model, consisting of randomly distributed graphite nanoregions, rolled graphene nanosheets, and a microporous structure. Its porous and disordered structure contributes to its impressive sodium-ion battery capacity. Furthermore, the range of precursors for hard carbon is very wide; coal, bark, rice husks, and starch can all be used as raw materials, making it low-cost and environmentally friendly. The preparation process of hard carbon materials includes pretreatment, pre-carbonization, and carbonization. Some precursors require the use of chemicals (HNO3, NH4(HPO3)2, etc.) in the pretreatment, which may be harmful and polluting. Some pre-carbonization is carried out in a tube furnace under argon protection at 300℃ to 400℃, which consumes more argon. The carbonization temperature of hard carbon is generally between 1000℃ and 1600℃, which requires more electrical energy and a longer process time. Summary of the Invention

[0004] In view of the problems faced by existing starch-based hard carbon materials, the primary objective of this invention is to provide a method for preparing starch-based hard carbon materials, aiming to prepare hard carbon materials that combine excellent capacity, high energy density, and high-rate fast charging stability.

[0005] The second objective of this invention is to provide a powder-based hard carbon material prepared by the aforementioned method and its application in sodium-ion batteries.

[0006] A third objective of this invention is to provide a sodium-ion battery comprising the starch-based hard carbon material, and its negative electrode and negative electrode material.

[0007] Starch is one of the main raw materials for preparing hard carbon, but it is prone to foaming, making its properties difficult to control. Furthermore, to obtain ideal disorder and electrochemical properties, preparation at temperatures above 1000°C is generally required. To address this problem, this invention provides the following improvement:

[0008] A method for preparing a starch-based hard carbon material, comprising the following steps:

[0009] Step 1:

[0010] The aqueous solution containing starch raw material is first subjected to atmospheric pressure heat treatment, and then subjected to high pressure heat treatment in a closed container, and then separated to obtain material A; the temperature of the first atmospheric pressure heat treatment is above 50℃; the temperature of the second high pressure heat treatment is above 100℃;

[0011] Step 2:

[0012] Material A and the additives are modified by water slurry to obtain material B; the additives are alkaline or acidic components.

[0013] Step 3:

[0014] Material B is carbonized at a low temperature of 750℃ to 950℃ to obtain the starch-based hard carbon material.

[0015] To address the issues of unsatisfactory performance and stability of hard carbon products caused by the easy foaming of starch raw materials, this invention innovatively applies a two-stage heat treatment of starch raw materials under normal and high pressure, and further combines it with subsequent modification with additives and low-temperature carbonization treatment. This allows for the preparation of starch-based hard carbon at low temperatures. Moreover, it can optimize its physicochemical structure and improve its capacity, tap density, fast charging, and high-rate stability.

[0016] In this invention, the starch raw material can be any starch-containing raw material in the industry, such as at least one of wheat starch, corn starch, and potato starch.

[0017] In this invention, starch raw materials are dispersed in water and mixed to obtain the aqueous solution containing starch raw materials.

[0018] Preferably, the starch raw material is first dispersed in solution A, and then dispersed in water to obtain the aqueous solution containing the starch raw material; solution A is an aqueous solution containing at least one solute selected from calcium chloride, organic acid, chloroform, and alkali. The organic acid is, for example, at least one selected from acetic acid, malic acid, citric acid, and oxalic acid.

[0019] In this invention, starch raw materials are innovatively dispersed in solution A before being dispersed in water. This, combined with subsequent treatments such as atmospheric pressure-high pressure, further enhances the physicochemical structure of the hard carbon material, resulting in starch-based hard carbon materials with better fast charging and stability.

[0020] In this invention, the concentration of the solute in solution A is 1-5 M, and more specifically 3-4 M.

[0021] In this invention, the liquid-to-solid ratio of water to starch in the aqueous solution of starch raw material is 5-50 ml / g.

[0022] In this invention, the first stage of atmospheric pressure heat treatment is carried out in an open container.

[0023] In this invention, the atmosphere for the first stage of atmospheric pressure heat treatment is air.

[0024] In this invention, the temperature of the first stage of atmospheric pressure heat treatment is 50-90°C, and can be further 70-90°C.

[0025] In this invention, the first stage of atmospheric pressure heat treatment takes 0.5 to 1 hour.

[0026] In this invention, the system subjected to the first stage of atmospheric pressure heat treatment is placed in a sealed container and heated to undergo the second stage of high-pressure heat treatment. In this invention, the high-pressure heat treatment refers to the pressure (P = nRT / V) of the sealed system.

[0027] In this invention, the temperature of the second high-pressure heat treatment is 150℃~250℃; preferably 190℃~210℃.

[0028] In this invention, the second stage of high-pressure heat treatment lasts for 10 to 15 hours.

[0029] In this invention, after the second stage of high-pressure heat treatment is completed, the material A can optionally be obtained by water washing, alcohol washing, and drying.

[0030] In this invention, in step 2, the auxiliary agent is at least one of sodium hydroxide and potassium hydroxide, preferably potassium hydroxide. The use of potassium hydroxide as an auxiliary agent can further synergistically optimize the physicochemical characteristics of starch-based hard carbon and further enhance its recycling performance.

[0031] Preferably, the weight ratio of material A to the additive is 1:1 to 5; more preferably, it is 1:2 to 4. At the preferred ratio, the physicochemical characteristics of starch-based hard carbon can be further synergistically optimized, and its recycling performance can be further enhanced.

[0032] In this invention, material A is pre-dispersed in water, and then additives are added for mixing and modification; or, the additives are pre-dissolved in water, and then material A is added for mixing and modification. This invention also shows that pre-dispersing material A in water, followed by adding additives for mixing and modification, allows for synergistic effects with other processes, resulting in more battery-compatible physicochemical structures and superior electrochemical performance.

[0033] In this invention, the volume-to-weight ratio of material A to water is 10–80 mL / g.

[0034] In this invention, the temperature of the modification stage is 60–95°C, and can be further 75–85°C.

[0035] In this invention, the modification treatment time is 1 to 3 hours.

[0036] In this invention, low-temperature carbonization is carried out in a protective atmosphere. The protective atmosphere is at least one of nitrogen, an inert gas, a hydrogen-nitrogen mixture, and an inert gas-hydrogen mixture.

[0037] In this invention, based on the combination of the aforementioned processes, hard carbon materials that combine excellent capacity, tap density, fast charging, and stability can be obtained under low-temperature conditions.

[0038] In this invention, the low-temperature carbonization temperature is 800–900°C, preferably 840–860°C. Thanks to the combination of components and processes, it is possible to construct sodium-electric compatibility physicochemical characteristics at relatively low temperatures, further enhancing its cycling performance in sodium-electric systems.

[0039] In this invention, the low-temperature carbonization time is 1 to 3 hours.

[0040] In this invention, the starch-based hard carbon material is obtained by low-temperature carbonization followed by acid treatment, water washing, alcohol washing, and drying.

[0041] The present invention also provides a starch-based hard carbon material prepared by the preparation method described above.

[0042] The preparation method described in this invention can endow the prepared material with more physicochemical properties that are compatible with sodium batteries. When applied to sodium batteries, it can achieve high energy density, high capacity, and high rate stability.

[0043] The present invention also includes the application of sodium-ion batteries and their components prepared from the starch-based hard carbon material described in the present invention, based on conventional methods and principles.

[0044] The present invention also provides a negative electrode material for a sodium-ion battery, comprising a negative electrode active material, wherein the negative electrode active material includes the starch-based hard carbon material.

[0045] In this invention, the negative electrode material, apart from containing the starch-based hard carbon material described in this invention, may have other conventional components and parts.

[0046] For example, in the negative electrode active material, the content of the starch-based hard carbon material is 50 wt.% or more, preferably 80 wt.% or more; further, it can be the starch-based hard carbon material of the present invention.

[0047] The negative electrode material of the present invention may also contain binders and conductive agents known in the industry;

[0048] In the negative electrode material described in this invention, the content of the negative electrode active material is 75–95 wt.%.

[0049] The present invention also provides a negative electrode for a sodium-ion battery, comprising a current collector and a negative electrode material composite thereon, wherein the negative electrode material is the negative electrode material comprising the starch-based hard carbon material described in the present invention.

[0050] In the negative electrode of this invention, in addition to the starch-based hard carbon material described in this invention, other components such as current collectors can be known.

[0051] The present invention also provides a sodium-ion battery comprising the negative electrode described herein.

[0052] The sodium-ion battery of this invention, apart from containing the starch-based hard carbon material described herein, can have other conventional components and structures. For example, it can be a solution-type sodium-ion battery, comprising a cell composed of a positive electrode, a separator, and a negative electrode, and an electrolyte soaking the cell. Alternatively, it can be a solid-state or semi-solid-state sodium-ion battery, comprising a cell composed of a positive electrode, a solid electrolyte, and a negative electrode.

[0053] Beneficial effects

[0054] This invention, through the aforementioned combined process, can break down the association between starch molecules, allowing them to solidify into pre-carbon on the surface in a disordered state. Combined with additive modification and low-temperature carbonization, this effectively solves problems such as starch volume expansion and structural collapse when heated. Furthermore, it can optimize its physicochemical structure, giving it a sodium-electric compatibility physicochemical structure, thereby enabling the production of starch-based hard carbon materials with excellent capacity, rate capability, and fast-charging performance at low temperatures. Attached Figure Description

[0055] Figure 1 Here is a SEM image of the hard carbon from Example 1;

[0056] Figure 2 The charge-discharge curve of the half-cell using the material of Example 1 as the electrode material is shown.

[0057] Figure 3 SEM image of the carbon material in Example 2;

[0058] Figure 4 Here is a SEM image of the carbon material in Example 4;

[0059] Figure 5 Here is a SEM image of the carbon material in Comparative Example 1;

[0060] Figure 6 The image shows the SEM image of the carbon material in Comparative Example 2. Detailed Implementation

[0061] The carbon material of this invention can be used as a negative electrode material in secondary batteries, especially suitable for sodium-ion batteries.

[0062] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the following description, in conjunction with embodiments, will further explain the invention. It should be noted that the methods described below are further explanations of the invention and should not be construed as limiting it.

[0063] Example 1

[0064] (1) Slowly add 2g of starch raw material (corn starch) to 40ml of deionized water with magnetic stirring. Keep it in an open container, in air atmosphere, at normal pressure, at a temperature of 80℃ and a stirring speed of 600-800r / min for 30min to obtain product A system.

[0065] (2) Transfer the product A system to a 100ml high-pressure reactor, seal the container and heat it to 200℃ for high-pressure reaction for 12h; after the heat preservation is completed, depressurize and separate the solid and liquid, and wash with deionized water and ethanol alternately 2-3 times, and then dry in a vacuum drying oven at 80℃ for 12h to obtain product B.

[0066] (3) After grinding and weighing product B, disperse it in deionized water (liquid-solid ratio of 40-45 ml / g). While magnetically stirring, add the auxiliary agent (KOH, where the mass ratio of product B to auxiliary agent is 1:3). Stir at 80°C for 1 hour to modify the mixture. Place the stirred solution in a drying oven and dry at 100°C for 14-18 hours.

[0067] (4) The dried solid is ground into powder and placed in a ceramic boat. After being wrapped with carbon cloth for protection, it is placed in a tube furnace and protected with argon gas. It is carbonized at 850℃ for 2 hours with a heating rate of 1℃ / min. After carbonization, it is naturally cooled to room temperature.

[0068] (5) Prepare a sufficient amount of 1M HCl solution, put the carbonization product into the HCl solution and stir magnetically for 30 minutes to fully react and remove KOH. Then filter and filter repeatedly with deionized water (the filtrate is neutral during washing) and ethanol. Dry under vacuum at 80°C for 12 hours to finally obtain product C (starch-based hard carbon material). Figure 1 The image shows the SEM image of product C. The SEM characterization clearly shows that there are many pores on the surface of the material. This structure can provide storage sites for sodium ions, thus enabling sodium-ion batteries to have good capacity.

[0069] The prepared starch-based hard carbon material was mixed evenly with conductive carbon black and PVDF at a mass ratio of 7:2:1. An appropriate amount of NMP (N-methylpyrrolidone) was added to prepare a slurry. After stirring thoroughly for 6 hours, the slurry was evenly coated onto copper foil using a coating machine. After vacuum drying at 60°C for 12 hours, a surface density of 5 mg / cm³ was obtained. 2 The negative electrode sheet.

[0070] A CR2025 coin cell sodium-ion battery was assembled in a glove box using a 1 mol / L NaPF6 solution in ethylene glycol dimethyl ether (DME) as the electrolyte, glass fiber as the separator, and a sodium metal sheet as the counter electrode. It was discharged at 1000 mA / g at room temperature, followed by 100 charge-discharge cycles at 50 mA / g, with the test voltage range being 0.01 V to 2.50 V.

[0071] Battery cycle performance such as Figure 2 As shown in Table 1, the initial discharge specific capacity was 255.6 mAh / g, and the capacity retention rate after 100 cycles was 93.39%.

[0072] Example 2

[0073] Compared with Example 1, the only difference is that in step 3, the KOH is pre-dissolved in deionized water and then product B is slowly added. The remaining operation steps are the same as those in Example 1, and the materials obtained are tested using the same method as in Example 1.

[0074] Example 3

[0075] Compared with Example 1, the only difference is that in step 4, the carbonization temperature is changed to 750°C, the carbonization reaction time is 2 hours, and the heating rate during the carbonization stage is 2°C / min. The remaining operation steps are the same as those in Example 1, and the materials obtained are tested using the same method as in Example 1.

[0076] Example 4

[0077] Compared with Example 1, the only difference is that in step 4, the carbonization temperature is changed to 950°C, the carbonization reaction time is 2 hours, and the heating rate during the carbonization stage is 2°C / min. The remaining operation steps are the same as those in Example 1, and the materials obtained are tested using the same method as in Example 1.

[0078] Example 5

[0079] Compared to Example 1, the only difference is that in step 3, the amount of KOH used is changed so that its weight is twice the weight of product B. The remaining operating steps are the same as in Example 1, and the obtained materials are tested using the same methods as in Example 1.

[0080] Example 6

[0081] Compared to Example 1, the only difference is that in step 3, the amount of KOH used is changed so that its weight is four times that of product B. The remaining operating steps are the same as in Example 1, and the obtained materials are tested using the same methods as in Example 1.

[0082] Example 7

[0083] Compared with Example 1, the only difference is that in step 3, the auxiliary agent is sodium hydroxide. The remaining operation steps are the same as those in Example 1, and the materials obtained are tested using the same method as in Example 1.

[0084] Example 8

[0085] Compared with Example 1, the only difference is that the preparation process of product A in step 1 is changed. The difference in step (1) is: 2g of starch raw material is dispersed in 20ml of solution A (4M CaCl2 aqueous solution) and stirred for 30-40min. Then it is added to 20ml of deionized water for dispersion. The mixture is kept warm for 30min in an open container, under air atmosphere, normal pressure, temperature of 80℃ and stirring at 600-800r / min to obtain product A.

[0086] All other steps, operations, and parameters are the same as in Example 1.

[0087] Comparative Example 1

[0088] Compared with Example 1, the only difference is that the atmospheric pressure heat treatment in step 1 was not performed. Instead, starch and 40 mL of water were placed directly in a pressure vessel at room temperature for step 2 and subsequent treatments.

[0089] Comparative Example 2

[0090] Compared with Example 1, the only difference is that in step 2, high-pressure treatment is not performed. That is, product A from step 1 is dried and used as product B in step 3 and subsequent processing steps.

[0091] Comparative Example 3

[0092] Compared with Example 1, the only difference is that KOH is not added in step 3, while the other operations and parameters are the same as in Example 1.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, compared with the comparative example, the atmospheric pressure-high pressure processing technology described in this invention can achieve excellent performance and improve battery performance.

[0096] Furthermore, as shown in Examples 1 and 2, pre-dispersing product B in water and then combining it with additives can optimize the physicochemical structure of the product and improve its performance. As shown in Examples 1 / 3-4, the solution described in this invention differs from conventional heat treatment methods that require temperatures above 1000°C; superior performance can be obtained at lower temperatures.

[0097] Furthermore, as can be seen from Examples 1 and 7, using potassium hydroxide as an additive has better synergy with the scheme of the present invention, which can further facilitate the synergistic optimization of the physicochemical structure of hard carbon, enabling it to exhibit better electrochemical performance.

[0098] Furthermore, as can be seen from Examples 1 and 8, the preferred atmospheric pressure treatment process of this invention can further facilitate the synergistic optimization of the physicochemical structure of hard carbon, enabling it to exhibit superior electrochemical performance.

Claims

1. An application of a starch-based hard carbon material in the preparation of sodium-ion batteries, characterized in that, The starch-based hard carbon material is prepared by the following steps: Step 1: The starch raw material is first dispersed in solution A, and then dispersed in water to obtain the aqueous solution containing the starch raw material; solution A is an aqueous solution containing dissolved calcium chloride. The aqueous solution containing starch raw material is first subjected to atmospheric pressure heat treatment, and then subjected to a second high pressure heat treatment in a closed container, and then separated to obtain material A; the temperature of the first atmospheric pressure heat treatment is above 50℃; the temperature of the second high pressure heat treatment is above 100℃; Step 2: Material A and the additive are modified by water slurry to obtain material B; the additive is at least one of sodium hydroxide and potassium hydroxide; the weight ratio of material A to the additive is 1:1~5; The temperature during the modification stage is 60~95℃. The modification treatment time is 1~3 hours; Step 3: Material B is carbonized at a low temperature of 750℃~950℃ to obtain the starch-based hard carbon material.

2. The application as described in claim 1, characterized in that, Starch raw materials include at least one of wheat starch, corn starch, and potato starch.

3. The application as described in claim 1, characterized in that, The concentration of the solute in solution A is 1~5M.

4. The application as described in claim 1, characterized in that, The concentration of the solute in solution A is 3~4M.

5. The application as described in claim 1, characterized in that, In the aqueous solution containing starch raw materials, the liquid-to-solid ratio of water to starch raw materials is 5~50 ml / g.

6. The application as described in claim 1, characterized in that, The first stage of atmospheric pressure heat treatment was carried out in an open container; The atmosphere for the first stage of atmospheric pressure heat treatment is air; The temperature for the first stage of atmospheric pressure heat treatment is 50~90℃; The first stage of atmospheric pressure heat treatment takes 0.5 to 1 hour.

7. The application as described in claim 1, characterized in that, The system that underwent the first stage of atmospheric pressure heat treatment was placed in a sealed container and heated for the second stage of high pressure heat treatment. The temperature of the second stage of high-pressure heat treatment is 150℃~250℃; The second stage of high-pressure heat treatment takes 10-15 hours; After the second stage of high-pressure heat treatment is completed, the material A can be obtained by water washing, alcohol washing and drying.

8. The application as described in claim 1, characterized in that, The weight ratio of material A to additives is 1:2~4.

9. The application as described in claim 1, characterized in that, Material A is pre-dispersed in water, and then the additives are added and mixed for modification; or, the additives are pre-dissolved in water, and then material A is added and mixed for modification. The volume-to-weight ratio of material A to water is 10~80mL / g; The temperature during the modification stage is 75~85℃.

10. The application as described in claim 1, characterized in that, Low-temperature carbonization is carried out in a protective atmosphere; The protective atmosphere is at least one of nitrogen, an inert gas, a hydrogen-nitrogen mixture, and an inert gas-hydrogen mixture. The time for low-temperature carbonization is 1~3 hours; After low-temperature carbonization, the starch-based hard carbon material is obtained by acid treatment, water washing, alcohol washing, and drying.

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