Negative electrode hard carbon material, preparation method thereof, negative electrode composition, sodium ion secondary battery and application

Abstract

The present invention relates to a negative electrode hard carbon material, a method for preparing the same, a negative electrode composition, a sodium ion secondary battery, and a use thereof, the negative electrode hard carbon material satisfying the following conditions: the weight ratio C / P of elemental carbon to elemental phosphorus is 300-5000 and 0.50-0.90, with the meanings defined in the specification; and the specific surface area of the negative electrode hard carbon material measured by carbon dioxide isothermal adsorption and desorption is 5-50 m < 2 > / g. The sodium ion secondary battery with the negative electrode hard carbon material has excellent first coulombic efficiency, first discharge gram capacity and cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates generally to the field of energy storage technology, in particular to the field of sodium-ion secondary batteries. Specifically, the present application relates to a negative hard carbon material, a preparation method thereof, a negative electrode composition comprising the same, a sodium-ion secondary battery comprising the negative electrode composition, and the use of the sodium-ion secondary battery. BACKGROUND

[0002] In recent years, secondary batteries play an increasingly important role in people's production and life. Compared with lithium-ion secondary batteries, sodium-ion secondary batteries are favored by the industry due to the abundant reserves and low price of sodium elements, and many similarities in process routes with mature lithium-ion secondary batteries. Similar to lithium-ion secondary batteries, sodium-ion secondary batteries generally comprise a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and work through the repeated deintercalation, transfer, and transmission of sodium ions between the positive and negative electrodes. For the negative electrode of a secondary battery, a carbon-based material is usually used as the negative electrode. However, the sodium storage capacity of the carbon-based material used in the prior art, such as graphite, is limited, resulting in low capacity, and the first coulombic efficiency and cycle performance (cycle life) of the carbon-based material used in the prior art are also poor, which is difficult to meet the increasing demand of people. In view of this, there is still a need to develop a negative hard carbon material with improved electrochemical performance. SUMMARY

[0003] The present application is made in view of the above problems existing in the prior art.

[0004] In a first aspect, the present application relates to a negative hard carbon material for a sodium-ion secondary battery, wherein the weight ratio of carbon element to phosphorus element C / P is 300-5000, preferably 400-2000, more preferably 800-1200, or 800-1500, or 800-2000, or 1000-1500, more preferably 1000-2000, and

[0005] The negative hard carbon material satisfies:

[0006] 0.50-0.90, preferably 0.70-0.90, more preferably 0.75-0.90, or 0.80-0.90,

[0007] wherein, is the density of the negative hard carbon material measured by the specific gravity bottle method with dimethyl carbonate (DMC) as the test reagent in g / cm 3 ; is the density of the negative hard carbon material measured by the helium gas displacement method in g / cm 3 ; and

[0008] The specific surface area of the negative electrode hard carbon material measured by carbon dioxide isothermal adsorption and desorption is 5-50 m 2 / g, preferably 14-30 m 2 / g, or 15-28 m 2 / g, more preferably 15-25 m 2 / g.

[0009] The negative electrode hard carbon material of the present application has a specific C / P ratio, a specific carbon dioxide isothermal adsorption and desorption specific surface area, and satisfies a specific range of The carbon dioxide isothermal adsorption and desorption specific surface area reflects the amount of pores between 0.35-1.0 nm. The inventors found in the research that when the carbon dioxide adsorption and desorption specific surface area is within the limited range, the water content of the battery cell can be effectively avoided, the side reaction with the electrolyte can be reduced, the diffusion of the electrolyte can be promoted, and the battery cell impedance can be reduced, thereby improving the first coulombic efficiency, the first discharge gram capacity (gram capacity is also referred to as specific capacity), and the cycle life. In addition, reflects the following specific pore structure: the volume of the pore structure in the negative electrode hard carbon material into which helium molecules can enter but DMC molecules cannot enter, accounts for the proportion of the volume of the remaining part of the negative electrode hard carbon material other than the volume of the pore structure into which DMC molecules can enter and the carbon skeleton of the negative electrode hard carbon material, in other words, the volume of the pore structure into which He molecules can enter in the pore structure into which DMC molecules cannot enter. Unexpectedly, the inventors accidentally found that when the The values, C / P ratio, and carbon dioxide isothermal adsorption and desorption specific surface area are simultaneously within the range defined in the present application, the first coulombic efficiency, the first discharge gram capacity, and the cycle life of the negative electrode hard carbon material are obviously improved compared to The first coulombic efficiency, the first discharge gram capacity, and the cycle life of the negative electrode hard carbon material, especially the first discharge gram capacity, are obviously improved when any one or more of the values, C / P ratio, and carbon dioxide isothermal adsorption and desorption specific surface area are not within the range defined in the present application.

[0010] In a second aspect, the present application relates to a method for preparing the negative electrode hard carbon material according to the first aspect of the present application, comprising:

[0011] Step 1: mixing a carbon source and a phosphorus source, and then performing heat treatment, preferably heat treatment at 30-200°C, wherein the weight ratio of the phosphorus source to the carbon source on a dry weight basis is 0.1:1 to 1.0:1;

[0012] Step 2: pre-carbonizing the product obtained in step 1 under inert gas protection at 350-600°C, and then cooling, optionally washing the product with deionized water to a water content of 0.1-5 wt.%, and then optionally crushing and sieving to obtain a pre-carbonized product;

[0013] ​Step 3: The pre-carbonized product obtained in Step 2 is treated with a first acid solution at 60-90°C, followed by optional washing with deionized water until the product is ;

[0014] Step 4: The product obtained in Step 3 is treated with a second acid solution at 60-90°C, followed by optional washing with deionized water until the product is , and then dried;

[0015] Step 5: The product obtained in Step 4 is optionally crushed, and then subjected to a second carbonization at 700-1400°C, preferably 900-1300°C, under an inert atmosphere, preferably followed by cooling to room temperature, and optionally crushed and sieved;

[0016] Step 6: The product obtained in Step 5 is mixed with 2-15% of pitch based on the dry weight of the product, preferably the pitch has a softening point of less than 100°C, preferably the mixing is carried out under heating, preferably at a heating temperature of 90-150°C; and

[0017] Step 7: The product obtained in Step 6 is subjected to a third carbonization at 900-1300°C, preferably 1000-1200°C, under an inert atmosphere, followed by cooling, and optionally crushed and sieved.

[0018] The preparation method of the present application uses raw materials with low prices, has cost advantages, and the preparation method of the present application is simple and easy to implement.

[0019] In a third aspect, the present application relates to a negative electrode composition, which is a negative electrode composition for a sodium-ion secondary battery, comprising the negative electrode hard carbon material according to the first aspect of the present application.

[0020] In a fourth aspect, the present application relates to a sodium-ion secondary battery comprising the negative electrode composition according to the third aspect of the present application.

[0021] In a fifth aspect, the present application relates to the use of the sodium-ion secondary battery of the fourth aspect of the present application in an energy storage device for solar power generation, wind power generation, smart grid peak shaving, distributed power station, backup power supply or communication base station. DETAILED DESCRIPTION

[0022] In order to make the purposes, technical solutions and beneficial technical effects of the present application clearer, the present application will be described in detail below. It should be noted that the various aspects, features, embodiments and advantages described in the present application can be compatible and / or combined together.

[0023] Unless otherwise specified, the meanings of the scientific and technical terms in the present specification are the same as those generally understood by those skilled in the art.

[0024] In the present application, temperature is room temperature (25°C), atmosphere is air, and pressure is atmospheric pressure, unless otherwise specified.

[0025] In the present application, the term "gram capacity" is synonymous with "specific capacity" and both are capacity per 1 g of active material, unless otherwise specified, and is sometimes also referred to as capacity. "Discharge gram capacity", "charge gram capacity" are similarly interpreted.

[0026] In the present application, the term "current density" used in connection with charging and discharging of a battery is current per weight of active material, unless otherwise specified.

[0027] In the present application, nitrogen adsorption-desorption specific surface area refers to specific surface area measured using nitrogen as a test gas (e.g. by a specific surface area analyzer such as ASAP 2460); carbon dioxide adsorption-desorption specific surface area refers to specific surface area measured using carbon dioxide as a test gas (e.g. by a specific surface area analyzer such as ASAP 2460). Both can be used to characterize the pore structure inside a material, with the difference that carbon dioxide can interact more strongly with polar surfaces, thus being able to reflect more features inside the pores of a material, such as the number of polar sites like acidic sites.

[0028] The present application relates to a negative hard carbon material, a method for producing the same, a negative electrode composition comprising the same, a sodium-ion secondary battery comprising the negative electrode composition, and use of the sodium-ion secondary battery.

[0029] The present application will be described in detail below.

[0030] Negative hard carbon material

[0031] In a first aspect, the present application relates to a negative hard carbon material for a sodium-ion secondary battery, wherein the weight ratio of carbon element to phosphorus element C / P is 300-5000, preferably 400-2000, more preferably 800-1200, or 800-1500, or 800-2000, or 1000-1500, more preferably 1000-2000, and

[0032] The negative hard carbon material satisfies:

[0033] is 0.50-0.90, preferably 0.70-0.90, more preferably 0.75-0.90, or 0.80-0.90,

[0034] wherein, is the density of the negative hard carbon material in g / cm3measured by the pycnometer method using dimethyl carbonate (DMC) as a test reagent; 3 ​the density of the negative electrode hard carbon material measured by the helium gas replacement method in g / cm 3 and

[0035] the specific surface area of the negative electrode hard carbon material measured by carbon dioxide isothermal adsorption and desorption is 5-50 m 2 / g, preferably 14-30 m 2 / g, or 15-28 m 2 / g, more preferably 15-25 m 2 / g.

[0036] Unexpectedly, the inventors found in their research that the negative electrode hard carbon material of the present application has a particular pore structure, wherein the carbon dioxide isothermal adsorption and desorption specific surface area reflects the amount of pore diameters between 0.35-1.0 nm, and when the carbon dioxide adsorption and desorption specific surface area is within the defined range, it is possible to effectively avoid water content exceeding the standard in the battery cell, reduce side reactions with the electrolyte, promote the diffusion of the electrolyte and reduce the impedance of the battery cell, thereby improving the comprehensive performance such as the first coulombic efficiency, the first discharge gram capacity and the cycle life; the difference in the reciprocal of the density of the hard carbon material measured by the specific gravity bottle method and the helium gas replacement method using test reagents of different molecular sizes can well reflect these pore structures that contribute to the sodium storage capacity in the negative electrode hard carbon material of the present application as a porous material. Specifically, when using dimethyl carbonate (DMC) as the test reagent for testing by the specific gravity bottle method, the density represents the density obtained by dividing the mass of the negative electrode hard carbon material by the volume of the remaining part of the negative electrode hard carbon material other than the pore structure into which the DMC molecules can enter, represents the volume of the remaining part of the unit negative electrode hard carbon material other than the pore structure into which the DMC molecules can enter; similarly, when using helium gas as the test reagent for testing by the helium gas replacement method, the density represents the density obtained by dividing the mass of the negative electrode hard carbon material by the volume of the remaining part of the negative electrode hard carbon material other than the pore structure into which the helium molecules can enter, represents the volume of the remaining part of the unit negative electrode hard carbon material other than the pore structure into which the helium molecules can enter. In addition, in the present application, the density of the carbon skeleton of the negative electrode hard carbon material, i.e. the theoretical density of ideal graphite, is represented by 2.26 g / cm 3 represents the volume occupied by the carbon skeleton part of the unit negative electrode hard carbon material. On this basis, it is easy for those skilled in the art to understand that represents the volume of the pore structure in the unit negative electrode hard carbon material into which the helium molecules can enter but the DMC molecules cannot enter, ​represents the volume of the pore structure in the unit negative electrode hard carbon material into which the DMC molecules cannot enter, i.e., the volume of the pore structure into which the DMC molecules cannot enter, after further subtracting the volume of the remaining part of the carbon skeleton of the negative electrode hard carbon material from the volume of the remaining part of the negative electrode hard carbon material other than the pore structure into which the DMC molecules can enter. Further, represents the volume of the pore structure in the negative electrode hard carbon material into which the helium molecules can enter but the DMC molecules cannot enter, and the ratio of the volume of the pore structure into which the helium molecules can enter to the volume of the remaining part of the negative electrode hard carbon material other than the pore structure into which the DMC molecules can enter and the volume of the carbon skeleton of the negative electrode hard carbon material, in other words, the volume ratio of the pore structure into which the helium molecules can enter to the pore structure into which the DMC molecules cannot enter. According to the above description, it is easy for those skilled in the art to understand that whether or not there is a closed pore material in the negative electrode hard carbon material does not affect the value of , because for the closed pore structure, neither the DMC molecules nor the helium molecules can enter.

[0037] Further, the inventors studied the influence of the value of on the electrochemical performance of the negative electrode hard carbon material. After a large number of studies, the inventors found that when the value of , the C / P ratio and the specific surface area of carbon dioxide isothermal adsorption desorption of the negative electrode hard carbon material are within the ranges defined in the present application, the first coulombic efficiency, the first discharge gram capacity and the cycle life, especially the first discharge gram capacity of the negative electrode hard carbon material are obviously improved compared to the case where any one or more of the value of , the C / P ratio and the specific surface area of carbon dioxide isothermal adsorption desorption are not within the ranges defined in the present application.

[0038] In the negative electrode hard carbon material of the present application, the weight ratio of carbon element to phosphorus element C / P is 300-5000, for example, 400-2000, or 800-1200, or 800-1500, or 800-2000, or 1000-1500, or 1000-2000. As an example, the weight ratio of carbon element to phosphorus element C / P can be 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000, or within a range defined by any two of them. In some embodiments, the C / P ratio of the negative electrode hard carbon material is in the range of 800-1500, within which range it is beneficial to improve the first coulombic efficiency of the negative electrode hard carbon material; preferably, the C / P ratio of the negative electrode hard carbon material is in the range of 800-1200, within which range it is beneficial to simultaneously improve the first coulombic efficiency and the first discharge gram capacity of the negative electrode hard carbon material. In some embodiments, the C / P ratio of the negative electrode hard carbon material is 1000-2000, within the above preferred range, it is beneficial to simultaneously improve the first coulombic efficiency, the first discharge gram capacity and the comprehensive performance of cycle life of the negative electrode hard carbon material.

[0039] In some embodiments, the specific surface area of the negative electrode hard carbon material of the present application can be 5-50 m 2 / g, preferably 14-30 m 2 / g, or 15-28 m 2 / g, more preferably 15-25 m 2 / g. The carbon dioxide adsorption-desorption specific surface area of the negative electrode hard carbon material of the present application can be tested by the carbon dioxide adsorption-desorption test using the conventional determination method in the art, and the specific surface area can be calculated using the D-R theory model. As an example, the specific surface area of the negative electrode hard carbon material measured by the carbon dioxide adsorption isotherm can be 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0, 36.0, 37.0, 38.0, 39.0, 40.0, 41.0, 42.0, 43.0, 44.0, 45.0, 46.0, 47.0, 48.0, 49.0, 50.0 m 2 / g, or within a range defined by any two of them. In some embodiments, the carbon dioxide adsorption-desorption specific surface area of the negative electrode hard carbon material is within a range of 15-28 m 2 / g, within which range it is beneficial to simultaneously improve the first coulombic efficiency and the first discharge gram capacity of the negative electrode hard carbon material; preferably, the carbon dioxide specific surface area of the negative electrode hard carbon material is 15-25 m 2 / g, within which preferred range it is beneficial to simultaneously improve the first coulombic efficiency, the first discharge gram capacity, and the cycle life performance of the negative electrode hard carbon material.

[0040] In the negative electrode hard carbon material of the present application, is 0.50-0.90, preferably 0.70-0.90, more preferably 0.75-0.90, or 0.80-0.90. As an example, may be 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, or within a range defined by any two of them. When within the above range, it is beneficial to improve the first coulombic efficiency and the first discharge gram capacity of the negative electrode hard carbon material. Preferably, is 0.75-0.90, within the above preferred range, it is advantageous to simultaneously improve the first coulombic efficiency, the first discharge gram capacity and the cycle life comprehensive performance of the negative hard carbon material; more preferably, is 0.80-0.90, within the range, it is advantageous to further improve the first discharge gram capacity of the negative hard carbon material.

[0041] In some embodiments, the negative hard carbon material of the present application has a first coulombic efficiency of In some embodiments, the negative hard carbon material of the present application has a first discharge gram capacity of 3 , preferably 1.2 to 1.4 g / cm 3 . represents the density of the negative hard carbon material measured by the pycnometer method with dimethyl carbonate (DMC) as the test reagent, in g / cm 3 . As an example, may be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 g / cm 3 , or a range defined by any two of them.

[0042] In some embodiments, the negative hard carbon material of the present application has a first coulombic efficiency of In some embodiments, the negative hard carbon material of the present application has a first discharge gram capacity of 3 , preferably 1.9 to 2.2 g / cm 3 . represents the density of the negative hard carbon material measured by the helium gas displacement method, in g / cm 3 . As an example, may be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2 g / cm 3 , or a range defined by any two of them.

[0043] In some embodiments, the phosphorus (P) content of the negative electrode hard carbon material of the present invention may be from 0.020% to 0.500%, preferably from 0.040% to 0.100%, based on the total weight of the negative electrode hard carbon material. As an example, the P content may be 0.020, 0.025, 0.030, 0.040, 0.050, 0.060, 0.070, 0.080, 0.090, 0.100, 0.110, 0.120, 0.130, 0.140, 0.150, 0.160, 0.170, 0.180, 0.190, 0.200, 0.210, 0.220, 0.230, 0.240, 0.250, 0.260, or 0.270%. The percentages are defined as follows: 0.280, 0.290, 0.300, 0.310, 0.320, 0.330, 0.340, 0.350, 0.360, 0.370, 0.380, 0.390, 0.400, 0.410, 0.420, 0.430, 0.440, 0.450, 0.460, 0.470, 0.480, 0.490, 0.500%, or any two thereof, based on the total weight of the negative electrode hard carbon material.

[0044] In some embodiments, the volume average particle size D of the negative electrode hard carbon material of the present invention v The diameter of 50 can be 3-20 μm, preferably 4-10 μm. Those skilled in the art will readily understand that the D of the negative electrode hard carbon material... v A particle size of 50 refers to the cumulative volume distribution curve of the particle size distribution of the negative electrode hard carbon material, where particles smaller than this particle size value and particles larger than this particle size value each account for 50% of the total volume of the negative electrode hard carbon material. v The particle size of 50 can be measured using methods conventionally used in the art, such as laser diffraction using a Malvern 3000 laser particle size analyzer. As an example, the D of the negative electrode hard carbon material... v The particle size can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 μm, or within the range defined by any two of them.

[0045] In some embodiments, the nitrogen specific surface area of ​​the negative electrode hard carbon material of the present invention can be 1-20 m². 2 / g, preferably 2.5-9.0 m 2 / g, or 4.0-8.0 m 2 / g, more preferably 2.5-8.0 m 2 / g. The nitrogen specific surface area of ​​the negative electrode hard carbon material of the present invention can be measured by conventional measurement methods in the art, for example, referring to... The determination was performed using the BET method for gas adsorption of solid materials. As an example, the nitrogen specific surface area of ​​the negative electrode hard carbon material can be 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, or 20.0 m². 2 / g, or within the range defined by either or both. In some embodiments, the nitrogen specific surface area of ​​the negative electrode hard carbon material is in the range of 2.5-6.5 m². 2 Within the range of / g, this is beneficial for simultaneously improving the initial coulombic efficiency and initial discharge specific capacity of the anode hard carbon material. Preferably, the nitrogen specific surface area of ​​the anode hard carbon material is 4.0-8.0 m². 2 / g, within the above preferred range, is beneficial to simultaneously improve the overall performance of the first coulombic efficiency, first discharge specific capacity and cycle life of the negative electrode hard carbon material.

[0046] Preparation method of anode hard carbon material

[0047] A second aspect of the present invention provides a method for preparing a negative electrode hard carbon material according to the first aspect of the present invention, comprising the following steps:

[0048] Step 1: Mix the carbon source and the phosphorus source, and then perform heat treatment, preferably at 30-200°C, wherein the weight ratio of the phosphorus source to the carbon source on a dry weight basis is 0.1:1 to 1.0:1.

[0049] Step 2: Pre-carbonize the product obtained in Step 1 at 350-600℃ under an inert gas atmosphere, then cool, and optionally wash with deionized water until the product... Then, optionally crush and sieve to obtain the pre-carbonized product;

[0050] Step 3: Treat the pre-carbonized product obtained in Step 2 with a first acid solution at 60-90°C, and then optionally wash with deionized water until the product... ;

[0051] Step 4: Treat the product obtained in Step 3 with a second acid solution at 60-90°C, and then optionally wash with deionized water until the product is dry. Then dry;

[0052] Step 5: The product obtained in Step 4 is optionally pulverized, and then subjected to a second carbonization at 700-1400°C, preferably 900-1300°C, under an inert atmosphere. Preferably, it is then cooled to room temperature and optionally pulverized and sieved.

[0053] Step 6: Mix the product obtained in Step 5 with 2-15% asphalt based on the dry weight of the product. Preferably, the asphalt has a softening point of less than 100°C. Preferably, the mixing is carried out under heating, preferably at a heating temperature of 90-150°C.

[0054] Step 7: The product obtained in Step 6 is subjected to a third carbonization at 900-1300℃, preferably 1000-1200℃, under an inert atmosphere, followed by cooling, and optionally crushing and sieving.

[0055] The preparation method of the present invention will be described in detail below.

[0056] Step 1

[0057] In step 1, the carbon source and the phosphorus source are mixed and then heat-treated, preferably at 30-200°C, wherein the weight ratio of the phosphorus source to the carbon source on a dry weight basis is 0.1:1 to 1.0:1.

[0058] The preparation method of the present invention does not have particular requirements on the type of carbon source used, but preferably, in some embodiments, the carbon source can be selected from biomass and / or coal. Preferably, the biomass can be selected from one or more of biomass polymers, bamboo, coconut shells, walnut shells, apricot shells, jujube pits, peach shells, palm shells, camellia shells, and pine nut shells, more preferably from one or more of biomass polymers, bamboo, coconut shells, apricot shells, and walnut shells. Preferably, the biomass polymer can be selected from one or more of starch, cellulose, lignin, and chitosan, more preferably from one or more of starch, lignin, and cellulose. Preferably, the coal can be selected from one or more of anthracite, bituminous coal, and lignite.

[0059] Similarly, the preparation method of the present invention does not have particular requirements on the type of phosphorus source used, and phosphorus sources commonly used in the art can be used. Preferably, in some embodiments, the phosphorus source may be selected from one or more of ammonium dihydrogen phosphate, sodium tripolyphosphate, phytic acid, phosphoric acid, sodium dihydrogen phosphate, and potassium dihydrogen phosphate. More preferably, the phosphorus source may be selected from one or more of ammonium dihydrogen phosphate, phosphoric acid, and sodium dihydrogen phosphate, preferably one or more of ammonium dihydrogen phosphate and phosphoric acid, and more preferably phosphoric acid. When ammonium dihydrogen phosphate and / or phosphoric acid are used as the phosphorus source, the initial coulombic efficiency and discharge specific capacity of the prepared negative electrode hard carbon material can be further improved compared with the use of sodium dihydrogen phosphate as the phosphorus source. More preferably, the phosphorus source is selected from phosphoric acid. When phosphoric acid is used as the phosphorus source, the discharge specific capacity of the prepared negative electrode hard carbon material can be further improved compared with the use of sodium dihydrogen phosphate and / or ammonium dihydrogen phosphate as the phosphorus source.

[0060] In some embodiments, the carbon source and phosphorus source can be mixed using methods commonly employed in the art. For example, the materials can be mixed in a container under mechanical stirring.

[0061] In some embodiments, the mixture obtained by mixing is heat-treated, preferably at 30-200°C, for example, by drying for 1-24 hours. As an example, the temperature for heat-treating the mixture can be within the range defined by 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200°C, or any two of these. Similarly, as an example, the time for heat-treating the mixture can be within the range defined by 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 hours, or any two of these.

[0062] In step 1, the weight ratio of the phosphorus source to the carbon source, on a dry weight basis, can be from 0.1:1 to 1.0:1. Within this defined weight ratio range, it is advantageous to obtain a negative electrode hard carbon material with a desired C / P ratio range, a desired carbon dioxide specific surface area, and a desired pore structure. Consequently, compared to weight ratios outside this range, the prepared negative electrode hard carbon material exhibits improved initial coulombic efficiency and initial discharge specific capacity, especially the initial discharge specific capacity. As an example, the weight ratio of the phosphorus source to the carbon source, on a dry weight basis, can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, or within the range defined by any two of these.

[0063] Step 2

[0064] Step 2: The product obtained in Step 1 is pre-carbonized at 350-600°C under an inert gas atmosphere, then cooled, and optionally washed with deionized water until the product... Then, optionally, it is crushed and sieved to obtain the pre-carbonized product.

[0065] The present invention does not have any particular requirements on the type of inert gas used in step 2, and any inert gas commonly used by those skilled in the art can be used. For example, the inert gas can be selected from one or more of nitrogen, helium, argon, etc.

[0066] Step 2 involves pre-carbonizing the product obtained in Step 1 at a temperature of 350-600°C, preferably 350-450°C. Within this temperature range, compared to pre-carbonization temperatures outside this range, it is advantageous to obtain a negative electrode hard carbon material with a desired C / P ratio range, a desired carbon dioxide specific surface area, and a desired pore structure, thereby achieving improved initial discharge specific capacity. As an example, the pre-carbonization temperature can be within the range defined by 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600°C, or any two of these.

[0067] The time for pre-carbonizing the product obtained in step 2 is not particularly limited and can be, for example, 0.5-12 h, such as 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0 h, or any two of them.

[0068] The pre-carbonization temperature can affect the C / P ratio and pore structure of the resulting hard carbon anode material. It should be noted that the pre-carbonization temperature should not be too high or too low, as this can adversely affect the C / P ratio and pore structure, thereby negatively impacting the initial coulombic efficiency, specific capacity, and cycle life.

[0069] The present invention does not have any special requirements for the cooling process in step 2, and any cooling method commonly used by those skilled in the art can be adopted. For example, direct cooling or indirect cooling methods, such as air cooling or water cooling, can be used.

[0070] Similarly, the present invention does not have any special requirements for the pulverization method, and pulverization methods commonly used by those skilled in the art can be used, such as air jet mills, mechanical mills, sand mills, ball mills, etc.

[0071] After cooling, step 2 may also optionally include a washing step of the cooled product, for example, washing with a washing liquid. As will be readily understood by those skilled in the art, the term "optionally" means that the step may or may not be present. For example, when cooling the product... Washing is not necessary when the product is cooled; however, washing is necessary when the pH of the cooled product is less than 3 to ensure the product's pH remains stable. Preferably, even in the cooling product Deionized water is also used for washing to remove impurities. Furthermore, those skilled in the art will readily understand that the expression "the pH of the product" refers to the pH of the product itself, but in practice it can refer to the pH of the washing solution, such as the pH of the washing solution when washing with deionized water at a weight ratio of deionized water to the washed substance of 1:1 to 10:1, or the pH of the filtrate during filtration. pH can be measured using methods commonly used by those skilled in the art, such as using a pH meter.

[0072] In some embodiments, preferably, after washing with deionized water, the resulting product is dried, for example, by baking, to facilitate subsequent processes. The preparation method of the present invention does not have special requirements for the drying process; drying methods commonly used by those skilled in the art can be employed.

[0073] In some embodiments, step 2, after optional crushing and sieving, yields a pre-carbonized product with a D... v 50 Particle size is 3-80 μm, preferably 5-60 μm. As an example, the pre-carbonized product can be pulverized to D... v 50 Particle sizes of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 μm, or any two of these.

[0074] Step 3

[0075] Step 3: Treat the pre-carbonized product obtained in Step 2 with a first acid solution at 60-90°C, and then optionally wash with deionized water until the product... .

[0076] The term "acid treatment" as used herein refers to acid treatment methods commonly used by those skilled in the art. For example, "acid treatment" may refer to immersing the product obtained in step 2 in an acid solution for treatment, followed by direct filtration or filtration after cooling to room temperature.

[0077] In some embodiments, the first acid solution (e.g., an aqueous solution) used in this invention is a mixture of hydrochloric acid and nitric acid, wherein the weight ratio of hydrochloric acid (HCl) to nitric acid, based on solute, can be from 1.5:1 to 2.0:1, for example, 1.5:1, 1.7:1, 1.74:1, 1.8:1, or 2.0:1. The concentration of the first acid (the total mass of solutes in hydrochloric acid and nitric acid) in the solution (aqueous solution) can be 5-30% by weight, for example, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 25.0, 30.0% by weight, or within the range defined by any two of these.

[0078] Preferably, the temperature for the first acid treatment of the pre-carbonized product obtained in step 2 in step 3 can be 60-90°C. As an example, the temperature of the first acid treatment can be within the range of 60, 65, 70, 75, 80, 85, 90°C, or any two of them.

[0079] Step 3 involves subjecting the pre-carbonized product obtained in step 2 to a first acid treatment for a period of 1-12 hours. As an example, the first acid treatment time can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours, or any two of these ranges.

[0080] In the first acid treatment, the weight (solvent + solute) of the first acid solution used is 2 to 10 times, preferably 2 to 5 times, of the weight of the pre-carbonized product obtained in step 2, for example 2, 3, 4, 5, 6, 7, 8, 9, 10 times, or within any two of these ranges.

[0081] In some embodiments, preferably, after the first acid treatment, the resulting product can be dried using a drying method commonly employed by those skilled in the art (e.g., baking) to facilitate subsequent processes.

[0082] Regarding the optional use of deionized water for washing, the pH of the product, and cooling, please refer to the description of step 2, which will not be repeated here.

[0083] Step 4

[0084] Step 4: Treat the product obtained in Step 3 with a second acid solution at 60-90°C, and then optionally wash with deionized water until the product is dry. Then dry.

[0085] In step 4, the total acid concentration of the second acid solution (i.e., the mass concentration of the total mass of the acid solutes) is 5-40% by weight, and / or the second acid solution is selected from one or more of hydrochloric acid, nitric acid, or hydrofluoric acid, preferably a mixed solution of hydrochloric acid, hydrofluoric acid, and nitric acid, wherein in the mixed solution of hydrochloric acid, nitric acid, and hydrofluoric acid, the weight ratio of hydrochloric acid to nitric acid based on solute can be 1.5:1 to 2.0:1, preferably 1.5:1 to 1.8:1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, or within the range defined by any two of them; the weight ratio of nitric acid to phosphoric acid based on solute can be 1:0.2 to 1:0.8, preferably 1:0.3 to 1:0.5, for example, 1:0.2, 1:0.3, 1:0. 4. The ratio of hydrochloric acid, nitric acid, and phosphoric acid by weight, based on solute, may be from 1.5:1:0.2 to 2.0:1:0.8, preferably from 1.5:1:0.3 to 1.8:1:0.5, for example, 1.5:1:0.2, 1.5:1:0.3, 1.5:1:0.8. The total acid concentration of the second acid solution may be 5.0, 1.5:1:0.8, 1.7:1:0.2, 1.74:1:0.32, 1.7:1:0.5, 1.7:1:0.8, 1.8:1:0.2, 1.8:1:0.3, 1.8:1:0.5, 2.0:1:0.2, 2.0:1:0.5, 2.0:1:0.8, or within the range defined by any two of these. As an example, the total acid concentration of the second acid solution may be 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 25.0, 30.0, 35.0, 40.0% by weight, or within the range defined by any two of these.

[0086] Preferably, the temperature at which the product obtained in step 3 is acid-treated in step 4 can be 60-90°C. As an example, the temperature at which the product obtained in step 3 is acid-treated in step 4 can be within the range of 60, 65, 70, 75, 80, 85, 90°C, or any two of these.

[0087] Step 4 involves acid treatment of the product obtained in step 3 for a period of 1-12 hours. As an example, the acid treatment time for the product obtained in step 3 in step 4 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 hours, or any two of these ranges.

[0088] In the second acid treatment, the weight (solvent + solute) of the second acid solution used is 2 to 10 times, preferably 2 to 5 times, of the weight of the product obtained in step 4, for example 2, 3, 4, 5, 6, 7, 8, 9, 10 times, or within any two of these ranges.

[0089] After acid treatment, the product obtained from the acid treatment is optionally washed with deionized water. For details regarding "optionally" using deionized water for washing, "the pH of the product," and "cooling," please refer to the description of step 2; these details will not be repeated here.

[0090] After washing, the resulting product can be dried for subsequent processes. This invention does not have specific requirements for the drying method; any drying method conventionally used by those skilled in the art can be employed. For example, the resulting product can be dried at a temperature of 40-120°C to remove moisture.

[0091] Step 5

[0092] Step 5: The product obtained in Step 4 is optionally pulverized and then carbonized in an inert atmosphere at 700-1400°C, preferably 900-1300°C. Preferably, it is then cooled to room temperature and optionally pulverized and sieved.

[0093] As an example, the temperature for the second carbonization can be within the range defined by 700, 800, 900, 1000, 1100, 1200, 1300, 1400 °C, or any two of these. Within the carbonization temperature range, it is advantageous for the prepared anode hard carbon material to simultaneously possess the defined C / P ratio, pore structure, and carbon dioxide specific surface area. Compared to the second carbonization temperature outside this range, the prepared anode hard carbon material can simultaneously achieve improved initial coulombic efficiency and initial discharge specific capacity, especially the initial discharge specific capacity.

[0094] There is no particular limitation on the time of the second carbonization and it can be, for example, 1-8 hours, 2-6 hours, 1, 2, 3, 4, 5, 6, 7, 8 hours, or any two of these.

[0095] In some embodiments, optionally, the product obtained in step 4 is pulverized; optionally, the high-temperature carbonization product is pulverized such that the volume average particle size D of the resulting negative electrode hard carbon material is... v 50 is in the range of 3-20 μm, preferably 4-10 μm. As an example, the high-temperature carbonization product can be pulverized to D... vThe particle size is 50 μm, defined as 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 μm, or any two of these. Similarly, referring to the description of step 2, the pulverization can be performed using pulverization methods conventionally used by those skilled in the art.

[0096] In addition, for information on "inert gas", "cooling", and "pulverization", please refer to the description of step 2, which will not be repeated here.

[0097] Step 6

[0098] The product obtained in step 5 is mixed with 2-15% asphalt based on the dry weight of the product. Preferably, the softening point of the asphalt is less than 100°C. Preferably, the mixing is carried out under heating, preferably at a heating temperature of 90-150°C.

[0099] In step 6, during mixing, the amount of asphalt relative to the product obtained in step 5 is 2-15%, preferably 5-10%. For example, the amount of asphalt relative to the total weight of the product obtained in step 5 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15% by weight, or within any two of these ranges. The inventors unexpectedly discovered during their research that, compared to no coating, coating with an amount of asphalt exceeding this range, or no coating but a third carbonization, coating with an amount of asphalt within this range is advantageous for obtaining a negative electrode hard carbon material with a desired C / P ratio range, desired carbon dioxide specific surface area, and desired pore structure. This is beneficial for obtaining improved first-efficiency, first discharge capacity, and cycle life, especially improved first discharge capacity and cycle life.

[0100] Preferably, in step 6, the asphalt used is a low softening point asphalt. As an example, the softening point of the asphalt is less than 100°C, for example, it can be 90, 80, 70, 60, 50, 40, 30°C, or within the range defined by any two of these. The softening point of the asphalt can be measured by methods conventionally used in the art, for example, by the ring and ball method according to national standards. Measurements were taken. The inventors discovered through research that, compared to high softening point asphalt or high-temperature asphalt, low softening point asphalt can significantly improve the electrochemical properties of hard carbon materials, such as cycle life.

[0101] In step 6, the product obtained in step 5 is mixed with asphalt. This mixing can be carried out under heat or by means of a solvent. When mixing is carried out by heat, the heating temperature is preferably higher than the softening point of the asphalt. For example, the heating temperature can be 90-150°C, such as 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150°C, or within the range defined by any two of these. When mixing is carried out by means of a solvent, solvents commonly used in the art can be used, such as aliphatic hydrocarbons like kerosene, diesel oil, etc., aromatic hydrocarbons like toluene, halogenated hydrocarbons like dichloromethane, cycloalkanes like cyclohexane, etc., or mixed solvents.

[0102] In step 6, the mixing of the product obtained in step 5 and the asphalt can be performed using mixing methods conventional in the art. For example, the mixing can be carried out at a rotation speed of 20-300 r / min for 1-8 hours, and then cooled to room temperature after mixing.

[0103] Step 7

[0104] The product obtained in step 6 is subjected to a third carbonization at 900-1300°C, preferably 1000-1200°C, under an inert atmosphere, followed by cooling and optionally pulverizing and sieving.

[0105] The third carbonization is beneficial for improving the conductivity of the coating layer while reducing defects and heteroatom content. The temperature of the third carbonization can be 900-1300°C, preferably 1000-1200°C. As an example, the temperature of the third carbonization can be within the range defined by 900, 1000, 1100, 1150, 1200, 1250, 1300°C, or any two of these, and / or the time of the third carbonization can be 1-8 hours, for example 2-6 hours, for example 1, 2, 3, 4, 5, 6, 7, 8 hours, or any two of these. Optionally, the hard carbon after the third carbonization can be pulverized to deagglomerate any potentially agglomerated hard carbon.

[0106] The "inert atmosphere" and "crushing" in step 7 can be found in the description of step 2, and will not be repeated here.

[0107] negative electrode composition

[0108] A third aspect of the present invention provides a negative electrode composition for use in sodium-ion secondary batteries, comprising a negative electrode hard carbon material according to a first aspect of the present invention.

[0109] In addition to the hard carbon negative electrode material of the present invention, the negative electrode composition (for sodium-ion secondary batteries) may also include conductive agents, binders, and any other substances that may be used by those skilled in the art as needed, such as dispersants and additives for improving stability.

[0110] In some embodiments, based on the dry weight of the negative electrode composition (for sodium-ion secondary batteries), the content of the negative electrode hard carbon material can be a commonly used amount in the art, for example, 60-95% by weight, such as 80-95% by weight.

[0111] There are no particular limitations on the type of conductive agent, as long as it enhances the conductivity of the negative electrode and does not adversely affect the performance of the hard carbon material of the negative electrode. Those skilled in the art can select conductive agents commonly used in the art according to actual needs. As an example, the conductive agent used in the negative electrode composition (for sodium-ion secondary batteries) may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the content of the conductive agent, based on the dry weight of the negative electrode composition (for sodium-ion secondary batteries), may be a commonly used amount in the art, for example, 1-10% by weight, or 2-5% by weight.

[0113] There are no particular limitations on the binder, as long as it enhances the adhesion between the particles of the negative electrode hard carbon material and its adhesion to the current collector, and does not adversely affect the performance of the negative electrode hard carbon material. Those skilled in the art can select according to actual needs. As an example, the binder used in the negative electrode composition for the sodium-ion secondary battery can be selected from polyfluoroolefin binders such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA) or their modified (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives, as well as one or more of styrene-butadiene rubber, acrylic resin, carboxymethyl cellulose, polyvinyl alcohol (PVA), etc.

[0114] In some embodiments, the binder content is 1-35% by weight, for example 2-5% by weight, based on the dry weight of the negative electrode composition (for sodium-ion secondary batteries).

[0115] The negative electrode composition may be in slurry form, meaning it may further include a solvent. The negative electrode composition may also be in dry form, meaning it does not include a solvent, for example, it may be in the form of a layer of negative electrode active material disposed on a negative electrode current collector.

[0116] Sodium-ion secondary batteries

[0117] A fourth aspect of the present invention provides a sodium-ion secondary battery. A sodium-ion secondary battery typically includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0118] In some embodiments, the sodium-ion secondary battery may also include an outer packaging for encapsulating the electrode assembly and electrolyte. For example, the outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or it may be a soft pack, such as a pouch, for example a soft pack made of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0119] There are no particular restrictions on the shape of sodium-ion secondary batteries; they can be cylindrical, square, or any other shape.

[0120] Sodium-ion secondary batteries can be prepared by methods commonly used in the art, for example, by forming a cell from positive electrode, negative electrode and separator through a winding process or a stacking process, and then injecting an electrolyte.

[0121] positive electrode

[0122] The positive electrode (or positive electrode sheet) includes a positive current collector and a layer of positive active material disposed on at least one surface of the positive current collector.

[0123] There are no particular limitations on the positive electrode current collector, and any positive electrode current collector commonly used by those skilled in the art can be used. As an example, the positive electrode current collector can be a metal foil such as aluminum foil, nickel foil, or a composite current collector. Composite current collectors can be formed by forming a metallic material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), 1,3-propanesulfonate lactone (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0124] This invention does not impose any particular limitation on the positive electrode active material; any positive electrode active material commonly used in the art can be employed. For example, the positive electrode active material may be selected from one or more of layered transition metal oxides or Prussian blue analogues. As an example, the layered transition metal oxide may have the general formula... M is selected from one or more of Mn, Fe, Ni, Co, Cr, Ti, Zn, V, Al, Zr, Ce, and Mg, and the general formula satisfies valence equilibrium. Furthermore, the layered transition metal oxide may also be doped with elements with high electronegativity, such as one or more of S, N, F, Br, Cl, I, and CN. As an example, the positive electrode active material may be selected from... , , , , , and One or more of the following.

[0125] In some embodiments, the content of the positive electrode active material, based on the total weight (dry weight) of the positive electrode active material layer, can be a commonly used amount in the art, such as 70-98% by weight, for example, 80-98% by weight.

[0126] In addition to the positive electrode active material, the positive electrode active material layer may also include binders, conductive agents, and any other optional additives such as thickeners.

[0127] There are no special requirements for the positive electrode conductive agent. As an example, the conductive agent may be selected from one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the content of the conductive agent may be 1-10% by weight, for example 2-5% by weight, based on the total weight (dry weight) of the positive electrode active material layer.

[0129] There are no special requirements for the positive electrode binder. As an example, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), styrene-butadiene rubber (SBR), waterborne acrylic resin, and carboxymethyl cellulose (CMC).

[0130] In some embodiments, the binder content may be 1-10% by weight, for example 1-5% by weight, based on the total weight (dry weight) of the positive electrode active material layer.

[0131] The positive electrode sheet can be prepared according to methods commonly used in this field.

[0132] For example, the positive electrode can be formed by uniformly dispersing the positive electrode active material, conductive agent, and binder in a solvent (e.g., N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; coating the slurry onto a positive electrode current collector, drying, and pressing.

[0133] Alternatively, the positive electrode can also be formed by uniformly dispersing the positive electrode active material, conductive agent, and binder in a solvent (e.g., N-methylpyrrolidone (NMP)) to obtain a positive electrode slurry; casting the positive electrode slurry on a separate carrier, drying it, separating the resulting positive electrode film from the carrier, and laminating it onto the positive electrode current collector.

[0134] negative electrode

[0135] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, said negative electrode active material layer comprising, for example, a negative electrode composition in a dried form according to the third aspect of the present invention. The negative electrode also forms an aspect of the present invention.

[0136] There are no particular limitations on the negative electrode current collector, and any negative electrode current collector commonly used by those skilled in the art can be used. As an example, the negative electrode current collector can be a metal foil such as copper foil, aluminum foil, or a composite current collector. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be formed by forming a metal material (copper, aluminum, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), but the present invention is not limited to these materials.

[0137] The negative electrode can be prepared according to methods commonly used in the art.

[0138] For example, the negative electrode can be formed by uniformly dispersing the negative electrode active material and optionally a conductive agent, binder and thickener in a solvent (e.g. N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, drying and pressing.

[0139] Alternatively, the negative electrode can also be formed by uniformly dispersing the negative electrode active material and optionally a conductive agent, binder and thickener in a solvent (e.g. N-methylpyrrolidone (NMP) or deionized water) to form a negative electrode slurry; casting the negative electrode slurry on a separate carrier, drying it, separating the resulting negative electrode film from the carrier and laminating it onto a negative electrode current collector.

[0140] electrolytes

[0141] The electrolyte acts as a conductor of ions between the positive and negative electrodes. There are no particular limitations on the electrolyte, and it can be selected as needed. For example, the electrolyte can be at least one of solid electrolytes, gel electrolytes, and liquid electrolytes (i.e., electrolyte solutions).

[0142] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an organic aprotic solvent and an electrolyte sodium salt.

[0143] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0144] In some embodiments, the electrolyte sodium salt may be selected from sodium hexafluorophosphate (SFC). Sodium tetrafluoroborate () Sodium perchlorate Sodium hexafluoroborate ( Sodium difluorosulfonamide (NaFSI), sodium difluoromethylsulfonamide (NaTFSI), sodium trifluoromethylsulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate ( Sodium difluorodioxanol phosphate (NaDFOP) and sodium tetrafluorooxanol phosphate (NaTFOP) are among one or more of these.

[0145] In some embodiments, the concentration of sodium ions in the electrolyte is 0.2-2 mol / L, for example 0.5-1.0 mol / L.

[0146] In some embodiments, the electrolyte may optionally include additives. As an example, the additives may include those that aid in the formation of a negative electrode film or a positive electrode film, and may also include additives that improve battery performance, such as those that improve the battery's high-temperature or low-temperature performance.

[0147] diaphragm

[0148] There are no particular limitations on the membrane, and commonly used porous membranes with electrochemical and chemical stability can be used, such as single-layer or multi-layer films made of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. When using a solid electrolyte, the membrane may be omitted.

[0149] use

[0150] The fifth aspect of the invention provides the use of the sodium-ion secondary battery according to the fourth aspect of the invention in energy storage devices for solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

[0151] Those skilled in the art will understand that the sodium-ion secondary battery of the fourth aspect of the present invention can also be used for other purposes. For example, the sodium-ion secondary battery can be used as a power supply or energy storage unit in mobile devices (e.g., mobile phones), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, electric bicycles, electric scooters, etc.), electric trains, etc.

[0152] Examples

[0153] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0154] I. Preparation Examples

[0155] Example 1

[0156] Hard carbon materials are prepared as follows:

[0157] (1) Take 100g of moso bamboo (D V 50 g of 75 μm and 50 g of phosphoric acid aqueous solution (concentration 40% by weight) are uniformly mixed. The amount of phosphoric acid (solute) is calculated on a dry weight basis relative to the mass of the carbon source (100 g of bamboo powder). The amount of the mixture was 20%. The resulting mixture was then dried in air at 80°C for 12 hours.

[0158] (2) The dried product from step (1) was pre-carbonized at 450°C under a nitrogen atmosphere for 2 hours. After cooling to room temperature, deionized water was added to the pre-carbonized product and the mixture was filtered until the pH of the product (i.e., the pH of the filtrate) was reached. The product was dried at 120°C for 12 hours and then cooled to room temperature. The dried product was then pulverized using an air jet mill (to its D...). v 50 particles with a diameter of 35 μm).

[0159] (3) The product obtained in step (2) was immersed in a 15% by weight mixed solution of hydrochloric acid and nitric acid at 80°C (where the weight ratio of hydrochloric acid solute to nitric acid solute was 1.74:1) at a weight ratio of 1:4 (the weight ratio of the product obtained in step (2) to the total weight of the hydrochloric acid and nitric acid mixed solution), and stirred at 500 rpm for 4 hours. Afterward, it was cooled to room temperature, and then the resulting mixture was filtered. The filtered product (filter cake, the same below) was then repeatedly washed with deionized water until the filtrate... The product was then dried at 120°C for 12 hours.

[0160] (4) Then, the product obtained in step (3) was immersed at 80°C in a mixed solution of hydrochloric acid, nitric acid, and hydrofluoric acid with a total concentration of 20% by weight (where the weight ratio of hydrochloric acid solute, nitric acid solute, and hydrofluoric acid solute was 1.74:1:0.32) at a weight ratio of 1:4, and stirred at 500 rpm for 4 hours. Afterward, the resulting mixture was filtered. The filtered product (filter cake, hereinafter the same) was then repeatedly washed with deionized water until the product... Then dry at 120℃ for 12 hours.

[0161] (5) Then the dried product from (4) is pulverized until D is reached. v The particles were 6.0 μm in diameter and then subjected to a second carbonization at 1200 °C under an argon atmosphere for 5 hours. After naturally cooling to room temperature, the resulting product was sieved.

[0162] (6) The product obtained in step (5) is mixed with coal tar pitch (softening point 45℃) at a weight ratio of 100:5. The mixing equipment used is a VC mixer (Wuxi Sentuo VC-5) with heating function, the heating temperature is 120℃, the mixing speed is 100 r / min, the mixing time is 2h, and the mixture is allowed to cool naturally to room temperature after mixing.

[0163] (7) The product obtained in step (6) is subjected to a third carbonization at 1200°C under an argon atmosphere for 5 hours. After natural cooling to room temperature, the obtained product is crushed and sieved to obtain the negative electrode hard carbon material of Example 1, whose D v 50 particles have a diameter of 5.5 μm. It is 1.384 g / cm 3 , It is 2.038 g / cm³ 3 The phosphorus content is 0.0704% (based on 100% by weight of the anode hard carbon material, the same below), and the carbon dioxide specific surface area is 15.22 m². 2 / g.

[0164] Example 2

[0165] Except for adjusting the amount of phosphoric acid to 30% in step (1) (i.e., the amount of phosphorus source relative to the amount of carbon source is 30% by weight, the same below), everything else is the same as in Example 1.

[0166] D of the pre-carbonized product in Example 2 v 50 particles with a diameter of 35 μm were used to obtain the D of the hard carbon anode material.v 50 particles have a diameter of 5.4 μm. 1.325 g / cm 3 , It is 2.063 g / cm³ 3 The phosphorus content is 0.0805%, and the carbon dioxide specific surface area is 17.65 m². 2 / g.

[0167] Example 3

[0168] Except for adjusting the amount of phosphoric acid to 40% in step (1), the rest is the same as in Example 1.

[0169] D of the pre-carbonized product in Example 3 v 50 particles with a diameter of 34 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.4 μm. It is 1.281 g / cm 3 , It is 2.069 g / cm³ 3 The phosphorus content is 0.0909%, and the carbon dioxide specific surface area is 20.18 m². 2 / g.

[0170] Comparative Example 1

[0171] Except for adjusting the amount of phosphoric acid to 5% in step (1), the rest is the same as in Example 1.

[0172] D of the pre-carbonized product in Comparative Example 1 v 50 particles with a diameter of 36 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.5 μm. It is 1.487 g / cm³ 3 , It is 1.996 g / cm³ 3 The phosphorus content is 0.0146%, and the carbon dioxide specific surface area is 13.0 m². 2 / g.

[0173] Comparative Example 2

[0174] Except for adjusting the amount of phosphoric acid to 110% in step (1), the rest is the same as in Example 1.

[0175] D of the pre-carbonized product in Comparative Example 2 v 50 particles with a diameter of 35 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.6 μm. It is 1.385 g / cm 3 , It is 2.133 g / cm3 The phosphorus content is 0.3289%, and the carbon dioxide specific surface area is 185.8 m². 2 / g.

[0176] Example 4

[0177] Except for the pre-carbonization temperature of 350°C in step (2), the rest is the same as in Example 3.

[0178] D of the pre-carbonized product in Example 4 v 50 particles with a diameter of 32 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.6 μm. It is 1.324 g / cm 3 , It is 1.928 g / cm³ 3 The phosphorus content is 0.0489%, and the carbon dioxide specific surface area is 15.75 m². 2 / g.

[0179] Example 5

[0180] Except for the pre-carbonization temperature of 550°C in step (2), the rest is the same as in Example 3.

[0181] D of the pre-carbonized product in Example 5 v 50 particles with a diameter of 34 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.6 μm. It is 1.347 g / cm³ 3 , It is 2.087 g / cm³ 3 The phosphorus content is 0.2023%, and the carbon dioxide specific surface area is 28.94 m². 2 / g.

[0182] Comparative Example 3

[0183] Except for the pre-carbonization temperature of 300°C in step (2), the rest is the same as in Example 3.

[0184] D of the pre-carbonized product in Comparative Example 3 v 50 particles with a diameter of 34 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.5 μm. It is 1.427 g / cm³ 3 , It is 1.745 g / cm³ 3 The phosphorus content is 0.0397%, and the carbon dioxide specific surface area is 12.78 m². 2 / g.

[0185] Comparative Example 4

[0186] Except for the pre-carbonization temperature of 700°C in step (2), the rest is the same as in Example 3.

[0187] D of the pre-carbonized product in Comparative Example 4 v 50 particles with a diameter of 36 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.2 μm. It is 1.434 g / cm³ 3 , It is 2.141 g / cm 3 The phosphorus content is 0.4391%, and the carbon dioxide specific surface area is 90.12 m². 2 / g.

[0188] Example 6

[0189] Except in step (1) replacing bamboo with coconut shells (Indonesia, D) v Except for 50 (75 micrometers), everything else is the same as in Example 3.

[0190] D of the pre-carbonized product in Example 6 v 50 particles with a diameter of 60 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.7 μm. It is 1.279 g / cm³ 3 , It is 2.048 g / cm³ 3 The phosphorus content is 0.0919%, and the carbon dioxide specific surface area is 17.18 m². 2 / g.

[0191] Example 7

[0192] Except for replacing bamboo with starch (corn starch from Jilin COFCO Biochemical Energy Sales Co., Ltd.) in step (1) and adjusting the amount of phosphoric acid to 30%, the rest is the same as in Example 3.

[0193] D of the pre-carbonized product in Example 7 v 50 particles with a diameter of 10 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.7 μm. 1.300 g / cm 3 , It is 2.079 g / cm³ 3 The phosphorus content is 0.0933%, and the carbon dioxide specific surface area is 23.59 m². 2 / g.

[0194] Example 8

[0195] Except in step (1) when bamboo is replaced with lignite (Shanxi Huayang Group, Except for adjusting the amount of phosphoric acid to 80%, the same as in Example 3 (micrometers).

[0196] D of the pre-carbonized product in Example 8 v 50 particles with a diameter of 5.4 μm were used to obtain the D-type hard carbon anode material. v 50 particles have a diameter of 5.2 μm. It is 1.265 g / cm³ 3 , It is 1.958 g / cm³ 3 The phosphorus content is 0.1103%, and the carbon dioxide specific surface area is 25.66 m². 2 / g.

[0197] Example 9

[0198] Except for replacing phosphoric acid with the same amount (by mass of solute, the same below) of ammonium dihydrogen phosphate in step (1), the rest is the same as in Example 3.

[0199] D of the pre-carbonized product in Example 9 v 50 particles with a diameter of 35 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.8 μm. It is 1.342 g / cm³ 3 , It is 1.968 g / cm³ 3 The phosphorus content is 0.0837%, and the carbon dioxide specific surface area is 22.57 m². 2 / g.

[0200] Example 10

[0201] Except for replacing phosphoric acid with the same amount of sodium dihydrogen phosphate in step (1), the rest is the same as in Example 3.

[0202] D of the pre-carbonized product in Example 10 v 50 particles with a diameter of 32 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 6 μm. It is 1.380 g / cm 3 , It is 1.951 g / cm³ 3 The phosphorus content is 0.1050%, and the carbon dioxide specific surface area is 20.36 m². 2 / g.

[0203] Example 11

[0204] Except for changing the second carbonization temperature to 700°C, everything else is the same as in Example 3.

[0205] D of the pre-carbonized product in Example 11 v 50 particles with a diameter of 36 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.7 μm. It is 1.363 g / cm 3 , It is 2.067 g / cm³ 3 The phosphorus content is 0.0927%, and the carbon dioxide specific surface area is 23.4 m². 2 / g.

[0206] Example 12

[0207] Except for changing the second carbonization temperature to 1400°C, everything else is the same as in Example 3.

[0208] D of the pre-carbonized product in Example 12 v 50 particles with a diameter of 34 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.8 μm. It is 1.326 g / cm³ 3 , It is 2.041 g / cm³ 3 The phosphorus content is 0.0889%, and the carbon dioxide specific surface area is 18.34 m². 2 / g.

[0209] Comparative Example 5

[0210] Except for changing the second carbonization temperature to 500°C, everything else is the same as in Example 3.

[0211] D of the pre-carbonized product in Comparative Example 5 v 50 particles with a diameter of 32 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.4 μm. It is 1.415 g / cm 3 , It is 2.135 g / cm 3 The phosphorus content is 0.0896%, and the carbon dioxide specific surface area is 51.2 m². 2 / g.

[0212] Comparative Example 6

[0213] Except for changing the second carbonization temperature to 1500°C, everything else is the same as in Example 3.

[0214] D of the pre-carbonized product in Comparative Example 6 v 50 particles with a diameter of 34 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.2 μm. It is 1.434 g / cm³ 3 , It is 1.709 g / cm³ 3 The phosphorus content is 0.0785%, and the carbon dioxide specific surface area is 15.8 m². 2 / g.

[0215] Example 13

[0216] Except for adjusting the weight ratio of the product obtained in step (5) to coal tar pitch to 100:2, everything else is the same as in Example 3.

[0217] D of the pre-carbonized product in Example 13 v 50 particles with a diameter of 37 μm were obtained as the D of the anode hard carbon material. v 50 particles have a diameter of 5.3 μm. It is 1.339 g / cm³ 3 , It is 2.108 g / cm³ 3 The phosphorus content is 0.0909%, and the carbon dioxide specific surface area is 26.13 m². 2 / g.

[0218] Example 14

[0219] Except for adjusting the weight ratio of the product obtained in step (5) to coal tar pitch to 100:10, everything else is the same as in Example 3.

[0220] D of the pre-carbonized product in Example 14 v 50 particles with a diameter of 36 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.8 μm. It is 1.322 g / cm 3 , It is 1.947 g / cm³ 3 The phosphorus content is 0.0933%, and the carbon dioxide specific surface area is 14.37 m². 2 / g.

[0221] Comparative Example 7

[0222] Except for adjusting the weight ratio of the product obtained in step (5) to coal tar pitch to 100:20, everything else is the same as in Example 3.

[0223] D of the pre-carbonized product in Comparative Example 7 v 50 particles with a diameter of 36 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 6.2 μm. It is 1.387 g / cm³ 3 , It is 1.674 g / cm³3 The phosphorus content is 0.0879%, and the carbon dioxide specific surface area is 4.02 m². 2 / g.

[0224] Comparative Example 8

[0225] Except for adjusting the weight ratio of the product obtained in step (5) to coal tar pitch to 100:0, everything else is the same as in Example 3.

[0226] D of the pre-carbonized product in Comparative Example 8 v 50 particles with a diameter of 35 μm were used to obtain the D of the hard carbon anode material. v 50 particles have a diameter of 5.3 μm. It is 1.474 g / cm³ 3 , It is 2.160 g / cm 3 The phosphorus content is 0.0912%, and the carbon dioxide specific surface area is 144.0 m². 2 / g.

[0227] Comparative Example 9

[0228] Except for adjusting the second carbonization temperature to 1400℃, omitting asphalt coating and the third carbonization, everything else is the same as in Example 2.

[0229] The Dv50 particle size of the pre-carbonized product in Comparative Example 9 was 36 μm, and the Dv50 of the resulting anode hard carbon material was... v 50 particles have a diameter of 5.5 μm. It is 1.365 g / cm 3 , It is 2.108 g / cm³ 3 The phosphorus content is 0.0791%, and the carbon dioxide specific surface area is 62.0 m². 2 / g.

[0230] II. Evaluation of Implementation Examples

[0231] 1. ρ DMC and ρ He

[0232] ρ DMC Test

[0233] 1) Wash the thermometer-equipped specific gravity bottle (25ml) with pure water, then clean it with ethanol, and then place it in an oven to dry thoroughly (the mercury thermometer should not be placed in the oven). Weigh the entire set of specific gravity bottles and record the mass as m1.

[0234] 2) Fill the specific gravity bottle with dimethyl carbonate (DMC), attach a thermometer (ensuring no air bubbles in the bottle), and immerse it in a constant temperature bath at 20±0.5℃ until the thermometer on the specific gravity bottle reaches 20℃, then stabilize for 10 minutes. Absorb any water overflowing from the test tube with filter paper, then cover with a small cover, remove, and dry. Weigh the specific gravity bottle (the entire set) and the DMC, and record the total weight as m2.

[0235] 3) Pour out the DMC from the specific gravity bottle, then clean it as in step 1) and dry it. Add approximately 1.0 g of the negative electrode hard carbon material prepared in the example or comparative example using a pipette, and attach a thermometer and cap. Weigh the total weight of the specific gravity bottle at this point and record it as m3.

[0236] 4) Pour half of the DMC solution into the specific gravity bottle (i.e., half the volume of the specific gravity bottle), and vacuum to remove bubbles until there are no more bubbles in the bottle. Then fill the bottle with DMC, attach the thermometer, and place it in a constant temperature bath at 20±0.5℃ until the thermometer on the specific gravity bottle reaches 20℃, and then stabilize for 10 minutes. Use filter paper to absorb the water overflowing from the test tube, then cover it with the small cover, remove it, and wipe it dry. Weigh the total weight of the specific gravity bottle (the whole set) and DMC at this point, and record it as m4.

[0237] True density ρ DMC Calculation formula: ρ0 is the density of dimethyl carbonate at 20℃, which is 1.0694 g / cm³. 3 .

[0238] ρ He Test

[0239] Refer to national standards The true density was measured using an Anton Pacanta Ultra PYC 1200e fully automated true density analyzer, as specified in Appendix D (Methods for Determining True Density) of "Graphite Anode Materials for Lithium-ion Batteries".

[0240] 2. P content and C / P ratio

[0241] Quantitative analysis of C and P elements was performed using X-ray photoelectron spectroscopy (Thermo Kalpha). The relative abundances of C and P elements were obtained directly from the XPS analysis report, and the C / P ratio was calculated using the following formula: .

[0242] 3. D v 50 particle size

[0243] The test was conducted using a Malvern 3000 laser particle size analyzer. Carbon was selected as the standard substance. Dishwashing liquid (Libai Fresh Lemon Dishwashing Liquid (product code 06920174736779)) mixed with water (volume ratio: dishwashing liquid: water = 1:3) was used as the dispersant. The instrument test parameters were set as follows: test time 10s, test count 3, light opacity 6~15%, stirring speed 2800 r / min, ultrasonic mode on, power 50%. The test was started using the Malvern 3000 laser particle size analyzer. Then, the first sintered product or cathode material was added to the sample cell, and the light opacity of the sample cell was adjusted to 6~15% by controlling the amount added. The instrument automatically repeated the test 3 times, and the average of the 3 tests was taken as the mean test result.

[0244] 4. Determination of specific surface area

[0245] Determination of the specific surface area of ​​hard carbon and nitrogen gas

[0246] 1.5g of hard carbon material was placed into the sample tube, followed by a glass packing rod, and then degassed (at 200℃). After degassed, the heating power was turned off. The sample tube was weighed after cooling to room temperature. The weighed sample tube was then placed into the surface area analyzer (ASAP 2460), and the sample mass was entered into the analysis file. The instrument was then clicked to begin the adsorption and desorption test. The results were automatically output after the test.

[0247] Determination of the specific surface area of ​​hard carbon dioxide

[0248] The test method is the same as that for "determination of the specific surface area of ​​hard carbon nitrogen", except that the adsorption and desorption gas source is changed from high-purity nitrogen (99.999%) to high-purity carbon dioxide (99.999%).

[0249] 5. Electrochemical performance testing

[0250] Manufacturing of button cells:

[0251] 0.45 g of anode hard carbon material, 0.025 g of SP (Swiss Temi high-conductivity carbon black SUPER-P), and 0.25 g of polyvinylidene fluoride (PVDF, purchased from SOLVAY, PVDF5130) adhesive solution (10% by mass, N-methylpyrrolidone (NMP) solvent) were uniformly mixed, and then N-methylpyrrolidone was added to prepare a viscous adhesive solution. The adhesive solution was coated onto aluminum foil (16 µm thick), and then baked in a vacuum drying oven at 120 °C for 12 h to obtain the anode electrode sheet (active material mass 4 mg / cm³). 2 Using a sodium metal sheet (Aladdin) as the counter electrode (thickness...) Using Waterman glass fiber as the diaphragm (675µm thick), and with a sodium ion concentration of 1mol / L... Solution (solvent is a mixture of EC and DMC, volume ratio is...) As an electrolyte, 2032 coin cells were assembled in an Ar atmosphere-protected glove box.

[0252] Manufacturing of 26700 cylindrical battery cells (26mm in diameter, 70mm in height):

[0253] (1) Preparation of the positive electrode sheet:

[0254] Layered oxides were mixed in a mass ratio of 96.5:1.5:1.5:0.5. Super-P, PVDF, and carbon nanotubes were then uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated on both sides of an aluminum foil (12 μm thick), with a single-sided areal density of 16.0 mg / cm³. 2 After drying and calendering (compacted density of 3.1 mg / cm³), 3 After vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain the positive electrode sheet.

[0255] (2) Preparation of negative electrode sheet:

[0256] The hard carbon material, Super-P, SBR, and CMC of this invention are mixed in a mass ratio of 94.5:1.5:2.5:1.5, and then uniformly dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil (8 μm thick), with a single-sided areal density of 9 mg / cm³. 2 (N / P ratio of charge is 1.10), after drying and calendering (compacted density is 0.90 mg / cm³). 3 After vacuum drying, and with the addition of nickel leads using an ultrasonic welding machine, a negative electrode sheet is obtained.

[0257] (3) Cell fabrication:

[0258] A PE film with a thickness of 16 μm (12 μm separator, double-sided coating, 2 μm on each side) coated with ceramic is placed between the positive and negative electrode plates. Then, the sandwich structure consisting of the positive electrode plate, negative electrode plate, and separator is wound up. The wound structure is then placed into the steel casing of a 26700 type cylindrical battery cell, and finally, an electrolyte (by weight percentage, composition: ...) is injected. , , , , (ethylene carbonate), , (The liquid injection coefficient is 4.0 g / Ah), and the battery is assembled.

[0259] First coulomb efficiency and charge / discharge capacity

[0260] After the 2032 coin cell battery was assembled, it was placed at 25°C and left to stand for 2 hours. Then, it was discharged at a constant current density of 20 mA / g to 0V, left to stand for 10 minutes, and then discharged again at a constant current density of 4 mA / g to 0V. The sum of the two discharge capacities was recorded as the initial discharge capacity. Afterward, it was left to stand for 1 minute and then charged at a constant current density of 20 mA / g to 2.0V. The charging capacity (initial charging capacity) was recorded. This constitutes one charge-discharge cycle. This is the first Coulomb efficiency.

[0261] Cycle retention rate

[0262] At 25℃, a 26700 cylindrical battery cell was charged at a constant current rate of 1C to 4.0V, then charged at a constant voltage rate until the current was less than or equal to 0.1C. After resting for 10 minutes, it was discharged at a constant current rate of 1C to 2.0V, and then rested for 10 minutes. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as the discharge capacity of the battery in the first cycle. The battery was subjected to 1000 charge-discharge cycles using the above method, and the discharge capacity of the 1000th cycle was recorded. The cycle retention rate at the 1000th cycle is calculated as the discharge capacity of the 1000th cycle / the discharge capacity of the first cycle multiplied by 100%.

[0263] The preparation conditions of some Examples 1-14 and Comparative Examples 1-9, and the electrochemical performance test results of sodium-ion secondary batteries containing the hard carbon materials prepared therefrom are summarized in Table 1 (the capacity in Table 1 is the discharge capacity measured by a 26700 cylindrical cell).

[0264] Table 1. Preparation conditions of Examples 1-14 and Comparative Examples 1-9, and electrochemical performance of sodium-ion secondary batteries containing the hard carbon negative electrode materials prepared therefrom.

[0265]

[0266] As can be seen from Table 1, relative to the C / P ratio, carbon dioxide specific surface area and Comparative Examples 1-9, which are not within the scope of this invention, and Examples 1-14, which are within the scope of this invention, all have superior overall performance in terms of initial coulombic efficiency, initial discharge capacity, and cycle life.

[0267] Comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that, compared with Comparative Examples 1-2 where the phosphorus source content is not within the specified range, the negative electrode hard carbon material of Examples 1-3 where the phosphorus source content is within the specified range has better first coulombic efficiency and first discharge specific capacity.

[0268] Comparing Examples 3-5 and Comparative Examples 3-4, it can be seen that, compared with Comparative Examples 3-4 where the pre-carbonization temperature is not within the defined range, the negative electrode hard carbon material of Examples 3-5 where the pre-carbonization temperature is within the defined range has a higher initial discharge capacity.

[0269] Comparing Examples 3 and 11-12 with Comparative Examples 5-6, it can be seen that, compared with Comparative Examples 5-6 where the second carbonization temperature is not within the defined range, the negative electrode hard carbon materials of Examples 3 and 11-12 where the second carbonization temperature is within the defined range have better initial discharge capacity and cycle life.

[0270] Comparing Examples 3 and 13-14 with Comparative Examples 7-8, it can be seen that, compared with Comparative Examples 7-8 where the asphalt coating amount is not within the specified range, the negative electrode hard carbon materials of Examples 3 and 13-14 where the asphalt coating amount is within the specified range have higher initial coulombic efficiency, initial discharge capacity and cycle life.

[0271] Comparing Example 3 and Comparative Example 9, Comparative Example 9, which does not undergo asphalt coating and a third carbonization step, will have a carbon dioxide specific surface area outside the defined range, resulting in a worse initial discharge capacity and cycle life.

[0272] Furthermore, as can be seen from Examples 6-10, when the type or amount of phosphorus source or the type of carbon source is changed, excellent overall performance in terms of initial coulombic efficiency, discharge capacity and cycle life can still be achieved.

[0273] The above description is merely an exemplary embodiment of the present invention. It should be noted that those skilled in the art can make improvements to the present invention without departing from the inventive concept, and all such improvements fall within the scope of protection of the present invention.

Claims

1. A hard carbon material for the negative electrode of a sodium-ion secondary battery, wherein the weight ratio of carbon to phosphorus (C / P) is 300-5000, preferably 400-2000, more preferably 800-1200, or 800-1500, or 800-2000, or 1000-1500, more preferably 1000-2000, and The negative electrode hard carbon material satisfies the following: The value is 0.50-0.90, preferably 0.70-0.90, more preferably 0.75-0.90, or 0.80-0.

90. in, The hard carbon negative electrode material was measured in g / cm³ using the hydrostatic bottle method with dimethyl carbonate (DMC) as the test reagent. 3 The density of the meter; The g / cm³ value of the hard carbon negative electrode material was determined by the helium gas displacement method. 3 The density of the calculation, and The specific surface area of ​​the negative electrode hard carbon material, measured by isothermal adsorption and desorption of carbon dioxide, is 5-50 m². 2 / g, preferably 14-30m 2 / g, or 15-28 m 2 / g, more preferably 15-25 m 2 / g.

2. The anode hard carbon material according to claim 1, wherein... Between 1.1 and 1.7 g / cm 3 Preferably, the concentration is 1.2 to 1.4 g / cm³. 3 Within the range; and / or Between 1.5 and 2.2 g / cm 3 The preferred concentration is 1.9 to 2.2 g / cm³. 3 Within the range.

3. The negative electrode hard carbon material according to claim 1 or 2, wherein the P content of the negative electrode hard carbon material is 0.020% to 0.500%, preferably 0.040% to 0.100%, based on the total weight of the negative electrode hard carbon material.

4. The negative electrode hard carbon material according to any one of claims 1-3, wherein the D of the negative electrode hard carbon material... v The particle size is 3-20 μm, preferably 4-10 μm.

5. The negative electrode hard carbon material according to any one of claims 1-4, wherein the specific surface area of ​​the negative electrode hard carbon material, measured by nitrogen isothermal adsorption-desorption, is 1-20 m². 2 / g, preferably 2.5-9.0 m 2 / g, or 4.0-8.0 m 2 / g, more preferably 2.5-8.0 m 2 / g.

6. A method for preparing the negative electrode hard carbon material according to any one of claims 1-5, comprising: Step 1: Mix the carbon source and the phosphorus source, and then perform heat treatment, preferably at 30-200°C, wherein the weight ratio of the phosphorus source to the carbon source on a dry weight basis is 0.1:1 to 1.0:

1. Step 2: Pre-carbonize the product obtained in Step 1 at 350-600℃ under an inert gas atmosphere, then cool, and optionally wash with deionized water until the product... Then, optionally crush and sieve to obtain the pre-carbonized product; Step 3: Treat the pre-carbonized product obtained in Step 2 with a first acid solution at 60-90°C, and then optionally wash with deionized water until the product... ; Step 4: Treat the product obtained in Step 3 with a second acid solution at 60-90°C, and then optionally wash with deionized water until the product is dry. Then dry; Step 5: The product obtained in Step 4 is optionally pulverized, and then subjected to a second carbonization at 700-1400°C, preferably 900-1300°C, under an inert atmosphere. Preferably, it is then cooled to room temperature and optionally pulverized and sieved. Step 6: Mix the product obtained in Step 5 with 2-15% asphalt based on the dry weight of the product. Preferably, the softening point of the asphalt is less than 100°C. Preferably, the mixing is carried out under heating, preferably at a heating temperature of 90-150°C. and Step 7: The product obtained in Step 6 is subjected to a third carbonization at 900-1300℃, preferably 1000-1200℃, under an inert atmosphere, followed by cooling, and optionally crushing and sieving.

7. The method according to claim 6, wherein the carbon source is selected from biomass and / or coal; Preferably, the biomass is selected from one or more of biomass polymers, bamboo, coconut shells, walnut shells, apricot shells, jujube pits, peach shells, palm shells, camellia shells, and pine nut shells, with biomass polymers, bamboo, coconut shells, apricot shells, and walnut shells being the most preferred. Preferably, the biomass polymer is selected from one or more of starch, cellulose, lignin, and chitosan, and more preferably from one or more of starch, lignin, and cellulose; Preferably, the coal is selected from one or more of anthracite, bituminous coal, and lignite.

8. The method according to claim 6 or 7, wherein the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, sodium tripolyphosphate, phytic acid, phosphoric acid, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; Preferably, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate, phosphoric acid, and sodium dihydrogen phosphate, more preferably phosphoric acid.

9. The method according to any one of claims 6-8, wherein the D of the pre-carbonized product obtained in step 2 v 50 Particle size is 3-80μm, preferably 5-60μm.

10. The method according to any one of claims 6-9, wherein the first acid solution in step 3 is a mixed solution of hydrochloric acid and nitric acid.

11. The method according to any one of claims 6-10, wherein the second acid solution in step 4 is a solution selected from one or more of hydrochloric acid, hydrofluoric acid and nitric acid, preferably a mixed solution of hydrochloric acid, hydrofluoric acid and nitric acid.

12. The method according to any one of claims 6-11, wherein one or more of the following conditions are satisfied: (i) The heat treatment in step 1 at 30-200°C lasts for 1-24 hours; (ii) The pre-carbonization time in step 2 is 0.5-12 hours; (iii) The treatment time with the first acid solution in step 3 at 60-90℃ is 1-12h; (iv) In step 4, the treatment time with the second acid solution at 60-90°C is 1-12 hours; (v) The second carbonization in step 5 takes 1-8 hours, for example 2-6 hours; (vi) The time for the third carbonization in step 7 is 1-8 hours, for example 2-6 hours.

13. A negative electrode composition for sodium-ion secondary batteries, comprising the negative electrode hard carbon material according to any one of claims 1 to 5.

14. A sodium-ion secondary battery comprising the negative electrode composition for a sodium-ion secondary battery according to claim 13.

15. The use of the sodium-ion secondary battery as described in claim 14 in energy storage devices for solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

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