A method for local ordering of a graphitic carbon material, graphitic carbon material produced thereby and use in a dual-ion battery

Abstract

The application discloses a method for local ordering of graphite carbon material, a graphite carbon material prepared by the method and application of the material in a dual-ion battery. The method according to the application comprises the following steps: 1) dispersing activated carbon and a Group VIII metal salt in water, stirring for 2-24 hours and mixing uniformly; 2) drying and grinding the mixed solution obtained in the step 1) to obtain a precursor, and then carbonizing the precursor by calcination under an inert atmosphere; and 3) cooling the product obtained in the step 2), washing the product with acid and water to remove residual metal particles, and drying to obtain a graphitized carbon positive electrode material. The preparation method according to the application changes the internal structure of the activated carbon from a completely disordered structure to an ordered-disordered structure by regulating the local microstructure of the activated carbon, and increases the designability of the graphite positive electrode material. The preparation method fully utilizes the ion adsorption mechanism of the channel in the activated carbon, simultaneously increases the anion intercalation capacity of the dual-ion battery in a high voltage region, and significantly improves the energy density.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of battery materials, and in particular relates to a method for locally ordering disordered carbon cathode materials, as well as a graphite carbon material prepared therefrom and the use of the material as a cathode material for a dual-ion battery. BACKGROUND

[0002] In order to meet the demand of national energy strategy, it is necessary to vigorously develop new energy storage devices with high specific energy and fast charging advantages. Due to the synergistic redox energy storage mechanism of anions and cations, the dual-ion battery using graphite as the cathode has attracted much attention in recent years, as it has the advantages of high working voltage, excellent power characteristics, low cost, etc. However, the traditional graphite cathode material relies on intercalation / deintercalation mechanism to store anions in the high voltage range (4.5-5.4V vs. Li + / Li), and exhibits a low specific capacity (~100mAh / g). Therefore, compared with traditional lithium ion batteries, the energy density of dual-ion batteries does not have a competitive advantage, and thus, it is crucial to stimulate other energy storage mechanisms in carbon cathode materials to improve the specific capacity. Lithium ion capacitors using activated carbon cathode materials store electric charge through physical adsorption. Combining the energy storage mechanisms of the two is expected to improve the energy density and power density of dual-ion batteries.

[0003] The prior art focuses on modifying the traditional graphite material at the sub-micron scale, such as surface modification of graphite material by inert Al2O3 and TiO2 materials, or expanding the interlayer spacing of graphite using strong oxidizing agents. These technologies have improved the cycle life and rate performance of dual-ion batteries to some extent. However, the physical and chemical properties of commercially available graphite are stable, and its surface is dense, making it difficult for modified molecules / ions to enter its bulk phase. The structure of highly graphitized carbon material is less adjustable, and only surface modification can be performed, so it is not possible to increase the storage sites of ions and improve the specific capacity of carbon cathode. The surface modification method of the prior art does not effectively improve the performance of graphite carbon material from the microstructure, and the preparation process of the above prior art is complex and has a higher production cost, so it is necessary to develop a carbon cathode material with higher capacity and higher stability. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to regulate the disordered region structure of activated carbon material at a more microscopic level, convert the disordered structure into a local ordered graphite structure, thereby obtaining a graphite carbon material with controllable proportion of ordered structure part and disordered structure part, and aims to stimulate the multiple energy storage mechanism of ions in the graphite carbon material positive electrode by increasing the active sites. The ordered graphite structure provides additional anion intercalation capacity and high-pressure stability, in addition, the remaining disordered structure has good ion adsorption capacity, thereby improving the ion storage capacity of the carbon positive electrode. At the same time, this process of converting irreversible sites into more stable ion storage sites significantly improves the cycle stability of the battery.

[0005] According to one aspect of the present application, one object of the present application is to provide a preparation method of a graphite positive electrode material, the method comprising the following steps:

[0006] 1) dispersing activated carbon and Group VIII metal salt in water, stirring for 2-24h to mix uniformly;

[0007] 2) drying and grinding the mixed solution obtained in step 1) to obtain a precursor, and then carbonizing by calcination under an inert atmosphere;

[0008] 3) cooling the product obtained in step 2), washing with acid and water to remove residual metal particles, and drying to obtain a graphitized carbon positive electrode material.

[0009] Preferably, the Group VIII metal salt in step 1) is selected from one or more of potassium ferricyanide, potassium ferrate, potassium trioxalate ferrate, ferric chloride, nickel acetate, and cobalt acetate, preferably potassium ferricyanide.

[0010] Preferably, the weight ratio of the activated carbon to the Group VIII metal salt in step 1) is 1:0.2-1:5, preferably 1:0.5-1:3, and more preferably 1:1-1:2.

[0011] Preferably, the activated carbon concentration in step 1) is 5g / L to 70g / L, preferably 10g / L to 40g / L.

[0012] Preferably, the Group VIII metal salt concentration in step 1) is 5g / L to 80g / L, preferably 10g / L to 60g / L.

[0013] Preferably, the drying temperature in step 2) is 70-160℃, preferably 70-100℃.

[0014] Preferably, the drying time in step 2) is 6-24h, preferably 10-14h.

[0015] Preferably, the carbonization temperature in step 2) is 600-1000°C, preferably 600-800°C, more preferably 750°C.

[0016] Preferably, the heating rate in step 2) is 1-10°C / min, preferably 1-8°C / min, preferably 5°C / min.

[0017] Preferably, the inert atmosphere in step 2) is selected from a nitrogen atmosphere or an argon atmosphere.

[0018] Preferably, the acid used in step 3) is dilute hydrochloric acid or dilute nitric acid.

[0019] Preferably, the drying temperature in step 3) is 80°C.

[0020] Preferably, the preparation method is as follows: 1.5 g of potassium ferricyanide is dissolved in 50 ml of deionized water, then 1 g of activated carbon is added to the solution and dispersed by magnetic stirring for 12 h, after being placed in an oven at 100°C for 20 h, the precursor is obtained by grinding; the precursor is placed in a tube furnace and heated to 750°C at a rate of 5°C / min, and held for 2 h, after natural cooling, residual metal substances are removed by repeated washing with dilute hydrochloric acid and deionized water, and the graphitized activated carbon material is obtained after drying in an oven at 80°C.

[0021] According to another aspect of the present application, another object of the present application is to provide a graphite positive electrode material prepared by the preparation method according to the present application, the graphite positive electrode material comprising ordered structure and disordered structure portions, wherein the ordered structure portion accounts for about 0-60% of the graphite positive electrode material, and the disordered structure portion accounts for about 40-100% of the graphite positive electrode material.

[0022] Preferably, the ordered structure portion accounts for about 5-40% of the graphite positive electrode material, and the disordered structure portion accounts for about 50-90% of the graphite positive electrode material.

[0023] More preferably, the ordered structure portion accounts for about 10-30% of the graphite positive electrode material, and the disordered structure portion accounts for about 65-85% of the graphite positive electrode material.

[0024] According to another aspect of the present application, another object of the present application is to provide the use of the graphite positive electrode material as a positive electrode material of a dual-ion battery.

[0025] According to another aspect of the present application, another object of the present application is to provide a dual-ion battery, which uses the graphite positive electrode material prepared by the preparation method according to the present application as a positive electrode material.

[0026] Beneficial effects

[0027] The technical solution according to the present application has the following advantages:

[0028] 1. The preparation method according to the present application changes the internal structure of activated carbon from completely disordered structure to ordered-disordered structure by regulating the local microstructure of activated carbon, thereby increasing the designability of graphite positive electrode materials.

[0029] 2. The preparation method according to the present application fully utilizes the ion adsorption mechanism of the pore channels in activated carbon, and at the same time increases the anion intercalation capacity of the double-ion battery in the high-voltage region. Therefore, compared with traditional lithium-ion capacitors and double-ion batteries, the energy density is significantly improved. The specific capacity of the battery is increased from 150 to 240 mAh / g, and the corresponding energy density is increased from 350 to 630 Wh / kg. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0031] Figure 1 X-ray diffraction spectra of graphitized activated carbon material prepared in Example 1, commercial activated carbon and commercial graphite carbon.

[0032] Figure 2 Raman spectrum of commercial activated carbon.

[0033] Figure 3 Raman spectrum of graphitized activated carbon material prepared in Example 1.

[0034] Figure 4 Raman spectrum of graphitized activated carbon material prepared in Comparative Example 2.

[0035] Figure 5 Raman spectrum of graphitized activated carbon material prepared in Example 2.

[0036] Figure 6 Raman spectrum of commercial graphite material.

[0037] Figure 7 Transmission electron microscope image of commercial activated carbon at low magnification.

[0038] Figure 8 Transmission electron microscope image of commercial activated carbon at high magnification.

[0039] Figure 9 Transmission electron microscope image of the graphitized activated carbon material prepared for Example 1 at low magnification.

[0040] Figure 10 Transmission electron microscope image of the graphitized activated carbon material prepared for Example 1 at high magnification.

[0041] Figure 11 Cyclic voltammogram of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 1 and a commercial activated carbon cathode.

[0042] Figure 12 Charge-discharge curve plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 1.

[0043] Figure 13 Rate capability comparison plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 1.

[0044] Figure 14 Cycle stability test plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 1.

[0045] Figure 15 Energy density-power density plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 1 and a commercial activated carbon cathode.

[0046] Figure 16 Charge-discharge curve plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 2.

[0047] Figure 17 Rate capability comparison plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 2.

[0048] Figure 18 Cycle stability test plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Example 2.

[0049] Figure 19 Charge-discharge curve of a dual-ion battery containing a commercial activated carbon cathode.

[0050] Figure 20 Rate capability comparison plot of a dual-ion battery containing a commercial activated carbon cathode.

[0051] Figure 21 Cycle stability test plot of a dual-ion battery containing a commercial activated carbon cathode.

[0052] Figure 22 Charge-discharge curve plot of a dual-ion battery containing a graphitized activated carbon cathode prepared for Comparative Example 2.

[0053] Figure 23 The graph shows a comparison of the rate performance of a dual-ion battery containing a graphitized activated carbon cathode prepared in Comparative Example 2.

[0054] Figure 24 The graph shows the cycle stability test results of a dual-ion battery containing a graphitized activated carbon cathode prepared in Comparative Example 2.

[0055] Figure 25 The charge-discharge curves of a dual-ion battery containing a commercial graphite carbon cathode are shown.

[0056] Figure 26 A comparison chart of the rate performance of dual-ion batteries containing commercial graphite carbon cathodes.

[0057] Figure 27 This is a graph showing the cycle stability test results of a dual-ion battery containing a commercial graphite carbon cathode. Detailed Implementation

[0058] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0059] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0060] In this document, all formulations or combinations of features or elements that can be formed by combining, intermixing, consolidating, abutting, etc., of the elements recited in the descriptions and drawings are specifically contemplated. In this document, all features or elements that are described in the description and / or shown in the drawings can be claimed as long as the features or elements are not mutually inconsistent. In this document, all ranges include all possible sub-ranges unless specifically stated otherwise. In this document, all percentages are by weight unless otherwise indicated. In this document, the terms "first," "second," "third," etc. are used merely as labels, and are not intended to impose ordinal, positional or hierarchical restrictions on the items described. In this document, terms such as "comprising," "including," "containing," etc. shall be construed as open-ended terms (meaning that the systems, methods, articles, etc. that include the recited elements do not exclude additional elements). In this document, the terms "coupled" and "connected" are used broadly and encompass both direct and indirect connections, as well as passive and active coupling or connection. Further, the terms "coupled" and "connected" are not restricted to optical, mechanical or electrical connections. In this document, the term "or" as used in a phrase such as "A or B" does not mean "both A and B." Rather, the term "or" is used in the inclusive sense, such that "A or B" means "A, B, or both A and B." In this document, the term "about" means ±10% of the stated value. In this document, the term "substantially" means contributions which are within normal experimental error when compared to the referenced quantity. In this document, the term "comprising" means "including, but not limited to."

[0061] If an amount or other numerical value or parameter is expressed in a range, a preferred range, or a series of upper and lower limits, it is to be understood that the range of values from any upper limit or preferred value of the range to the lower limit or preferred value of the range is specifically contemplated as being disclosed herein, whether or not the ranges are expressly disclosed. Further, when a range of values is recited herein, unless otherwise stated, the range is to be construed as including both the end points and all the integers and fractions within the range, unless otherwise indicated.

[0062] In this document, numerical values are to be construed in a functionally effective and complete manner with the precision of the number of significant figures of the numerical value. For example, the number 40.0 is to be construed as encompassing the range from 39.50 to 40.49.

[0063] Further, unless otherwise indicated, the reagents and solvents disclosed below are purchased from Dongguan Keluode Experimental Equipment Technology Co., Ltd. X-ray diffraction (XRD) is tested using an X-ray diffractometer with a model number of D-MAX 2200VPC; and Raman spectroscopy is tested using a Raman spectrometer with a model number of inVia; TEM is tested using a transmission electron microscope with a model number of F30. The constant current charge-discharge cell test of the dual-ion battery is performed on a blue battery test system (CT002A); the cyclic voltammetry curve is collected by a CHI760E electrochemical workstation. The proportion of ordered and disordered structures in the carbon material is calculated by fitting the peak area of the D band (representing disordered structure) and the G band (representing ordered structure) of the carbon material in the Raman spectrum, and then normalized.

[0064] The following examples are merely illustrative of the present application and are not intended to limit the scope of the application. Any modification of the application which adheres to the principle of the application will be considered to fall within the scope of the application. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0065] Example 1

[0066] The precursor was obtained by dispersing 1.5 g of potassium ferricyanide (purchased from Shanghai Maikelin Co., Ltd.) in 50 ml of deionized water, then adding 1 g of activated carbon into the solution and dispersing it by magnetic stirring for 12 h, and then fully grinding after being placed in an oven at 100 °C for 20 h; the precursor was placed in a tube furnace and heated to 750 °C at a rate of 5 °C / min, and held for 2 h, and then naturally cooled, and then washed repeatedly with dilute hydrochloric acid and deionized water to remove residual metal substances, and then dried in an oven at 80 °C to obtain a graphitized activated carbon material.

[0067] Figure 1 The XRD spectra of the graphitic positive electrode material prepared in this example, the existing commercial activated carbon (XFP01, purchased from Nanjing Xianfeng Nanometer Material Technology Co., Ltd.) and the commercial graphite carbon (KS-6, purchased from Dongguan Keluode Experimental Equipment Technology Co., Ltd.) can be seen from the comparison in the figure that the carbon material prepared according to this example has good crystallinity, indicating that the carbon material prepared contains ordered structure, however, compared with the commercial graphite, the intensity is weak and the half-peak width is wide, indicating that the carbon material also contains disordered structure (i.e. defects in the carbon material).

[0068] Example 2

[0069] Compared with Example 1, the carbonization temperature was changed to 850 °C, and other conditions were unchanged. From the Raman spectrum of Figure 5 , it can be calculated that the ordered structure of the carbon material prepared in this example accounts for 18%, and the corresponding disordered structure accounts for 82%.

[0070] Comparative Example 1

[0071] Commercial activated carbon was used as a comparison. From the XRD spectrum of Figure 1 , it can be seen that the diffraction peak of the commercial activated carbon is wide and weak, indicating that the crystallinity is low and the carbon atoms are arranged in disorder. In addition, from the Raman spectrum of Figure 2 , the ordered structure of the activated carbon accounts for 13.3%, and the disordered structure accounts for 86.7% (obtained by calculating their peak areas), which is the highest among several carbon materials. At the same time, from Figure 7 and Figure 8 are transmission electron microscope images of the commercial activated carbon at different magnifications, and it can also be observed that the carbon atoms in the commercial activated carbon are arranged in disorder.

[0072] Comparative Example 2

[0073] Compared with Example 1, the carbonization temperature was changed to 650 °C, and other conditions were unchanged. From the Raman spectrum of Figure 3 , it can be calculated that the ordered structure of the carbon material prepared in this comparative example 2 accounts for 14.6%, and the corresponding disordered structure accounts for 85.4%.

[0074] Comparative Example 3

[0075] This comparative example 3 directly uses a commercial graphite material (KS-6) as a comparison. From the XRD pattern of the commercial graphite material in Figure 1 The commercial graphite material can be seen from the XRD pattern that the commercial graphite material has strong diffraction peaks, and the half-width peak is narrow, indicating that it has higher crystallinity. Figure 6 The Raman spectrum of the commercial graphite material is shown in the figure, from which it can be observed that a strong G peak appears in the Raman spectrum of the commercial graphite material, indicating that there are more ordered carbon atom structures inside the material, and by calculating the peak area, it can be obtained that the disordered structure accounts for 58%, and the ordered structure accounts for 42%, which is the highest ordered degree among the above-mentioned several carbon materials.

[0076] Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 The Raman spectra of the commercial activated carbon, the graphitized activated carbon material prepared in Example 1, the graphitized activated carbon material prepared in Comparative Example 2, the graphitized activated carbon material prepared in Example 2, and the commercial graphite carbon material are shown in Figures 1-5, respectively. From the Raman spectra of the commercial activated carbon and the graphitized activated carbon material prepared in Example 1, it can be observed that the D and G bands of the commercial activated carbon are relatively strong, and the D and G bands of the graphitized activated carbon material prepared in Example 1 are relatively weak, indicating that the carbon atom structure of the graphitized activated carbon material prepared in Example 1 is more ordered than that of the commercial activated carbon. Figure 4 The ordered structure of the graphitized activated carbon material prepared in this example accounts for 16%, and the corresponding disordered structure accounts for 84%, which can be calculated from the area of the D and G bands in the Raman spectrum. Figure 7 and Figure 8 are transmission electron microscope images of the commercial activated carbon at different magnifications. Figure 9 and Figure 10 are high-resolution transmission electron microscope images of the graphitized activated carbon positive electrode material prepared in Example 1. From the images, it can be observed that the carbon atom structure of the graphitized activated carbon material prepared in Example 1 is more ordered than that of the commercial activated carbon. Figure 7 、 Figure 8 and Figure 9 、 Figure 10 From the comparison of the above-mentioned images, it can be seen that after the regulation, the carbon atom structure inside the activated carbon changes from a completely disordered structure to a mixed structure of ordered and disordered.

[0077] Test Example 1

[0078] Preparation of a double-ion battery positive electrode:

[0079] According to the conventional electrode preparation method in the art, the positive electrode materials in Examples 1 and 2 and Comparative Examples 1 to 3 are respectively uniformly mixed with a conductive agent super P and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 in an N-methyl pyrrolidone (NMP) solvent, and then uniformly coated on an aluminum foil by means of scraping, and after being fully dried in a vacuum oven at 80°C for 12h, the positive electrode sheet is obtained by cutting the aluminum foil into 10mm round sheets. The loading amount of the active material is 1.5±0.3mg / cm2 .

[0080] Assembly of dual-ion batteries:

[0081] In the R2032 type coin cell, the dual-ion battery positive electrode prepared above, the 14 mm diameter Li elemental negative electrode, and the glass fiber (GF / D) separator were used. After adding 150 μL of electrolyte (4M LiPF6 / EMC), the battery was encapsulated under a pressure of 50 kPa. All dual-ion batteries were allowed to stand for 12 hours before electrochemical testing, with a voltage window of 1.5–5.1 V. The rate performance of the dual-ion battery was evaluated by charge / discharge tests at current densities of 200, 400, 600, 800, and 1000 mA / g, and long-term cycle stability tests were conducted at a current density of 1 A / g.

[0082] Figure 11 The cyclic voltammetry curves for a dual-ion battery containing commercial activated carbon and the graphitized activated carbon cathode from Example 1 are shown below. Figure 11 The comparison shows that the graphitized activated carbon cathode prepared in Example 1 exhibited a pair of redox peaks in the high-voltage region, while no similar electrochemical behavior was observed in the commercial activated carbon cathode, indicating that anion insertion / extraction reactions occurred in the graphitized activated carbon cathode. Figure 12 The charge-discharge curves of the dual-ion battery containing the graphitized activated carbon cathode from Example 1 are shown below. Figure 12 It can be seen that the battery has a specific capacity of up to 240 mAh / g at a current density of 200 mA / g, and can still release a specific capacity of 95 mAh / g at 1000 mA / g, indicating that the graphite material prepared by Example 1 has excellent anion storage capacity. Figure 13 The graph shows the rate performance of the dual-ion battery containing the graphitized activated carbon cathode from Example 1. Figure 13 As can be seen from Example 1, the graphitized activated carbon cathode material prepared in Example 1 has good rate performance and reversibility. Figure 14 The graph shows the cycle performance of the dual-ion battery containing the graphitized activated carbon cathode from Example 1. Figure 14 As can be seen, the battery capacity slowly decreased to 82mAh / g after 600 charge-discharge cycles, indicating that the graphitized activated carbon cathode has good cycle stability. Figure 15 This is a comparison graph of the energy density and power density of dual-ion batteries containing the graphitized activated carbon cathode prepared in Example 1 and a commercial activated carbon cathode. Figure 15As can be seen, when the power density is 530 W / kg, the energy density can reach 630 Wh / kg (the energy density of commercial activated carbon cathode is only 350 Wh / kg). Even at 2850 W / kg, it can still release an energy density as high as 268 Wh / kg, indicating that the dual-ion battery containing the graphitized activated carbon cathode in Example 1 has good power-energy characteristics.

[0083] Figure 16 and Figure 17 The charge-discharge curves of the dual-ion battery containing the graphitized activated carbon cathode prepared in Example 2 are shown below. Figure 16 and Figure 17 The results show that the battery has a specific capacity of 165 mAh / g at a current density of 200 mA / g and 76 mAh / g at 1000 mA / g, indicating good rate performance and good ion storage capacity. Furthermore, after undergoing high-current testing, the battery's specific capacity recovered to over 90% of its original value, demonstrating the good reversibility of the graphite cathode prepared in Example 2. Meanwhile, from... Figure 18 Based on the long-cycle curves, the dual-ion battery containing the graphitized activated carbon cathode in Example 2 showed a relatively slow capacity decay to 56 mAh / g after 600 cycles.

[0084] Figure 19 and Figure 20 Charge-discharge curves for dual-ion batteries containing commercial activated carbon, from... Figure 19 and Figure 20 The rate test results show that the battery has a specific capacity of 114 mAh / g at a current density of 200 mA / g, but only 20 mAh / g at 1000 mA / g, indicating poor rate performance. Furthermore, after high-current testing, the battery's specific capacity cannot be recovered, even falling below 50% of its original value. Simultaneously, it can be observed that the activated carbon cathode exhibits rapid capacity decay when tested at low rates. Figure 21 The graph shows the cycle stability test results of a dual-ion battery containing a commercially available activated carbon cathode. Figure 21 The long-cycle curves show that the specific capacity of the dual-ion battery containing a commercially activated carbon cathode decays rapidly to 48 mAh / g after 600 cycles, indicating that the presence of numerous irreversible defect sites (disordered structure) in the carbon material leads to a decrease in battery reversibility. These data suggest that its overall electrochemical performance is poor.

[0085] Figure 22 and Figure 23 The graph shows the charge-discharge curves of a dual-ion battery containing the graphitized activated carbon cathode from Comparative Example 2. Figure 22 and Figure 23It can be seen from the battery in 200 mA / g current density has 158 mAh / g specific capacity, and 55 mAh / g at 1000 mA / g, in addition, after the large current test, the battery specific capacity cannot be restored, even less than 70% of the original; also can be observed battery capacity decay rapidly when the battery is tested at a small rate. In addition, Figure 24 The cycle stability test graph of the dual-ion battery containing the graphitized activated carbon positive electrode prepared in Comparative Example 2 is shown from Figure 24 As can be seen from the long cycle curve in the battery, the specific capacity of the dual-ion battery containing the graphitized activated carbon positive electrode in Comparative Example 2 is attenuated to 52 mAh / g after 600 cycles, indicating that there are still many irreversible defect sites in the graphitized activated carbon positive electrode material in Comparative Example 2.

[0086] Figure 25 And Figure 26 The charge-discharge curve graph of the dual-ion battery containing the commercial graphite positive electrode is shown from Figure 25 And Figure 26 It can be seen from the battery in 200 mA / g current density has 102 mAh / g specific capacity, the lowest specific capacity in several positive materials, which is due to the limited ion storage sites inside the graphite, and 43 mAh / g at 1000 mA / g, indicating that the narrow ion transmission channel in the graphite affects the rate performance. In addition, Figure 27 The cycle stability test graph of the dual-ion battery containing the commercial graphite carbon positive electrode is shown from Figure 27 As can be seen from the long cycle curve in the battery, the cycle stability of the dual-ion battery containing the commercial graphite positive electrode is good, and the capacity is 52 mAh / g after 600 charge-discharge cycles, which is related to the less defects inside and good oxidation resistance.

[0087] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be limited by the protection scope of the claims.

Claims

1. A method for preparing a graphite cathode material, the method comprising the following steps: 1) Disperse activated carbon and potassium ferricyanide in water and stir for 2-24 h to mix evenly. The weight ratio of activated carbon to potassium ferricyanide is 1:0.2 to 1:5, the concentration of activated carbon is 5 g / L to 70 g / L, and the concentration of potassium ferricyanide is 5 g / L to 80 g / L. 2) Dry and grind the mixed solution obtained in step 1) to obtain the precursor, and then calcine and carbonize it under an inert atmosphere. The drying temperature is 70-160℃, the drying time is 6-24h, the calcination and carbonization temperature is 600-1000℃, and the calcination and carbonization heating rate is 1-10℃ / min. 3) After cooling the product obtained in step 2), wash it with acid and water to remove residual metal particles, and then dry it to obtain graphitized carbon cathode material. The acid used for washing is dilute hydrochloric acid or dilute nitric acid, and the drying temperature is 80 ℃.

2. The preparation method according to claim 1, characterized in that, The weight ratio of activated carbon to potassium ferricyanide in step 1) is 1:0.5 to 1:3; The activated carbon concentration in step 1) is 10 g / L to 40 g / L; The concentration of potassium ferricyanide in step 1) is from 10 g / L to 60 g / L.

3. The preparation method according to claim 1, characterized in that, The weight ratio of activated carbon to potassium ferricyanide in step 1) is 1:1 to 1:

2.

4. The preparation method according to claim 1, characterized in that, The drying temperature in step 2) is 70-100℃; The drying time in step 2) is 10-14 hours; The roasting and carbonization temperature in step 2) is 600-800℃; In step 2), the roasting and carbonization heating rate is 1-8 ℃ / min; The inert atmosphere mentioned in step 2) is selected from a nitrogen atmosphere or an argon atmosphere.

5. The preparation method according to claim 1, characterized in that, The roasting and carbonization temperature in step 2) is 750℃; In step 2), the roasting and carbonization heating rate is 5 °C / min.

6. The preparation method according to claim 1, characterized in that, The preparation method is as follows: 1.5 g of potassium ferricyanide is dissolved in 50 mL of deionized water, and then 1 g of activated carbon is added to the solution and dispersed by magnetic stirring for 12 h. After being placed in an oven at 100 degrees Celsius for 20 h, the precursor is thoroughly ground to obtain a precursor. The precursor is placed in a tube furnace and heated to 750 degrees Celsius at 5 ℃ / min, held at that temperature for 2 h, and then allowed to cool naturally. The residual metal substances are removed by repeated washing with dilute hydrochloric acid and deionized water. After drying in an oven at 80 degrees Celsius, graphitized activated carbon material is obtained.

7. A graphite cathode material prepared by the preparation method according to any one of claims 1 to 6, the graphite cathode material comprising ordered and disordered structural portions, wherein the ordered structural portion accounts for 5-40% of the graphite cathode material and the disordered structural portion accounts for 50-90% of the graphite cathode material.

8. The graphite cathode material according to claim 7, characterized in that, The ordered structure portion of the graphite cathode material accounts for 10-30% of the graphite cathode material, and the disordered structure portion accounts for 65-85% of the graphite cathode material.

9. The use of the graphite cathode material according to claim 7 or 8 as the cathode material of a dual-ion battery.

10. A dual-ion battery, wherein the dual-ion battery uses the graphite cathode material prepared according to any one of claims 1 to 6 as the cathode material.

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