Composite positive electrode material for lithium battery and manufacturing method therefor

Abstract

Disclosed in the present invention are a composite positive electrode material for a lithium battery and a manufacturing method therefor. The method comprises: a grinding step: grinding CrO3 and FeS2 to a mixture having a uniform color; and a heating and sintering step: carrying out a heating reaction on the mixture to obtain a FeS2-doped Cr8O21 composite positive electrode material. The mass ratio of CrO3 to FeS2 is (10-20):1, the heating temperature is 260℃-270℃, and the constant-temperature duration is 8 h-18 h. The FeS2-doped Cr8O21 composite positive electrode material manufactured by the present invention has the characteristics such as small particle size, high purity, and low impurity content, and can effectively enhance discharge efficiency and electrochemical performance when applied to lithium batteries.

Description

Composite positive electrode material for lithium battery and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a composite positive electrode material for lithium batteries and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for renewable and clean energy worldwide, new energy technologies have ushered in an opportunity for rapid development. In particular, in the fields of portable electronic devices, electric vehicles, and smart grids, high-energy-density energy storage systems have become one of the key technologies. Lithium batteries have become the current mainstream energy storage technology due to their relatively high energy density, long cycle life, and good environmental adaptability. However, with the popularity of high-energy-density electronic devices, the market's performance requirements for lithium batteries are constantly improving, especially the pursuit of energy density and power density, prompting researchers to continuously explore new lithium battery electrode materials.

[0003] Lithium batteries are mainly composed of positive electrodes, electrolytes, and negative electrodes, and other core structures. Cr8O 21 As a new type of electrode material, it shows great potential as a lithium battery positive electrode material due to its high theoretical specific energy, high voltage platform, and high lithium storage capacity. Compared with traditional lithium battery positive electrode materials (lithium cobaltate, lithium manganate, lithium iron phosphate, etc.), Cr8O 21 can provide higher energy output to meet the market's demand for higher energy density batteries.

[0004] However, Cr8O 21 faces some challenges in practical applications. First, Cr8O 21 is usually in block form, has a large particle size and high viscosity, and is difficult to machine (grind, cut, etc.). Blocky Cr8O 21 has low crystallinity, which may cause large volume changes during charging and discharging, leading to stress concentration and material rupture, which seriously affects the discharge performance of the material. Second, in order to prepare high-purity Cr8O 21 , the reaction temperature and time must be strictly controlled by one-step pyrolysis of CrO3 to achieve its optimal electrochemical performance. These problems greatly limit the application of Cr8O 21 material in lithium batteries. In order to overcome the above challenges, modification of Cr8O 21 material has become a hot research topic. SUMMARY

[0005] The purpose of the present application is to solve the problem of blocky Cr8O 21The application discloses a preparation method of a composite positive electrode material for lithium batteries.

[0006] To achieve the above-mentioned purpose, the application provides a preparation method of a composite positive electrode material for lithium batteries.

[0007] Grinding step: grinding CrO3 and FeS2 into a mixture with uniform color;

[0008] Heating and sintering step: heating and reacting the mixture to obtain FeS2-doped Cr8O 21 composite positive electrode material;

[0009] The mass ratio of the CrO3 and the FeS2 is (10-20):1, the heating temperature is 260-270 DEG C, and the constant temperature time is 8-18 hours.

[0010] Optionally, the CrO3 and the FeS2 are subjected to drying pretreatment in advance before the grinding step.

[0011] Optionally, the grinding step is carried out in a dry environment, and the CrO3 and the FeS2 are separately ground and then mixed into a mixture with uniform color.

[0012] Optionally, the heating and reacting step has a temperature rising rate of 4-6 DEG C / min.

[0013] Optionally, oxygen or air is introduced during the heating and reacting step.

[0014] Optionally, the method further comprises: repeatedly carrying out the grinding step and the heating and sintering step to complete the reaction.

[0015] The application further provides a composite positive electrode material for lithium batteries obtained by the above preparation method.

[0016] Optionally, the composite positive electrode material for lithium batteries is a powder solid.

[0017] Optionally, the powder solid is a flaky Cr8O 21 coated with FeS2.

[0018] The application has the following beneficial effects:

[0019] 1. The application solves the problems of large particle size, high processing difficulty and poor discharge performance of the existing blocky Cr8O 21 The application introduces FeS2 as a nucleation site in the heating and decomposition process of CrO3, guides the Cr8O 21 to crystallize on the surface, and since the FeS2 is uniformly dispersed, small-particle-size Cr8O21 Crystal. This invention uses FeS2-doped Cr8O. 21 The resulting composite cathode material macroscopically appears as a powdered solid, wherein the powdered solid is flake-shaped Cr8O. 21 FeS2 is coated. Meanwhile, this invention unexpectedly discovered that a heating temperature of 260–270°C limits the growth of Cr8O. 21 Continue to generate Cr2O5 and Cr5O 12 The composite cathode material prepared by combining Cr2O3 and other byproducts has the characteristics of small particle size, high purity and few impurities.

[0020] 2. The FeS2-doped Cr8O prepared by this invention 21 When composite cathode materials are used in lithium batteries, during the discharge process of the lithium battery, FeS2 doped with Cr8O 21 The composite cathode material is a powdered solid, compared to bulk Cr8O 21 With a larger specific surface area, it is more conducive to the full wetting of the electrolyte and the rapid insertion and extraction of lithium ions, thereby significantly enhancing the discharge efficiency and electrochemical performance of the battery. In addition, the preparation method provided by this invention has the advantages of simple process, controllable reaction process and low preparation difficulty, and has good application prospects in the field of lithium batteries. Attached Figure Description

[0021] Figure 1 shows the thermogravimetric analysis diagram of CrO3.

[0022] Figure 2 shows Cr8O 21 SEM image.

[0023] Figure 3 shows the FeS2-doped Cr8O prepared in Example 1. 21 Composite cathode materials and Cr8O 21 XRD pattern of standard spectra.

[0024] Figure 4 shows the FeS2-doped Cr8O prepared in Example 1. 21 SEM image of the composite cathode material. Figure 5 shows the FeS2-doped Cr8O prepared in Example 2. 21 SEM image of the composite cathode material.

[0025] Figure 6 shows the FeS2-doped Cr8O prepared in Example 3. 21 SEM image of the composite cathode material.

[0026] Figure 7 shows the FeS2-doped Cr8O prepared in Example 1 and Comparative Example 2. 21 XRD patterns of composite cathode materials and FeS2.

[0027] Figure 8 is a comparison of the discharge volt-ampere curves of Examples 1-3 and Comparative Examples 1-3.

[0028] Figure 9 is a comparison chart of discharge volt-ampere curves of Example 1 and Comparative Examples 4-5.

[0029] Figure 10 is a comparison chart of discharge volt-ampere curves of Example 1 and Comparative Examples 6-7. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0031] The prior art Cr8O 21 Generally has a large particle size (3-6 pm) and high viscosity, and is difficult to remove from the crucible during processing, resulting in greater difficulty in mechanical processing, and poor discharge performance of the material. In order to reduce the particle size of Cr8O 21 and improve its discharge performance while reducing the difficulty of material processing, FeS2 is designed to be doped. Specifically, the present application provides a preparation method of a composite positive electrode material for lithium batteries, which comprises:

[0032] Grinding step: grinding CrO3 and FeS2 into a mixture with uniform color.

[0033] Before grinding, CrO3 and FeS2 are subjected to drying pretreatment in advance to remove excess moisture, and the grinding process is always carried out in a dry environment to prevent CrO3 and FeS2 from adhering to the mortar after absorbing water. At the same time, CrO3 and FeS2 are first ground separately and then mixed to obtain a mixture with uniform color. It can be understood that separate grinding and mixing make the contact area larger and the mixing more uniform.

[0034] The mass ratio of CrO3 to FeS2 is (10-20):1. When the content of FeS2 is higher, and lower than the above mass ratio, the particle size of Cr8O 21 is smaller, and cannot completely occupy the nucleation sites of FeS2, so that the number of Cr8O 21 particles attached to each FeS2 particle does not reach the optimal range; when the content of FeS2 is lower, and higher than the above mass ratio, the particle size of Cr8O 21 is larger, and the viscosity is higher, making the processing more difficult, for example, grinding is difficult, and it is difficult to form a powder with a large specific surface area.

[0035] Heating and sintering step: heating and reacting the mixture to obtain FeS2-doped Cr8O 21 composite positive electrode material.

[0036] The heating rate is 4-6℃ / min, when the temperature reaches 200℃, CrO3 gradually melts into liquid state, FeS2 particles are dispersed in the liquid CrO3 as nucleation sites, when the temperature reaches 260℃, CrO3 starts to decompose, and Cr8O 21 is easily crystallized at the nucleation sites. Because FeS2 particles are uniformly dispersed, the formed Cr8O 21 has smaller crystal grain size. Oxygen or air is also introduced during the heating process, which mainly functions to inhibit the decomposition rate of CrO3, and also can make the formed Cr8O 21 has smaller crystal grain size, and also can inhibit the excessive decomposition of Cr8O 21 into by-products such as Cr2O5, Cr5O 12 and Cr2O3. In addition, the present application surprisingly finds that the heating temperature of 260-270℃ can also limit the excessive decomposition of Cr8O 21 into by-products, so that the generated Cr8O 21 has higher purity and less impurities. Constant temperature for 8-18h can ensure complete reaction.

[0037] The method also comprises: repeatedly performing the grinding step and the heating and sintering step. Different amounts of CrO3 and FeS2 will result in different numbers of cycles. When the amount is large, multiple cycles can ensure complete reaction, while in the examples of the present application, the amount is small, so only 2 cycles are performed.

[0038] The present application also provides a composite positive electrode material for lithium batteries prepared by the above preparation method.

[0039] The composite positive electrode material for lithium batteries is in the form of a powder-like solid, and the powder-like solid is flaky Cr8O 21 coated with FeS2. Compared with blocky Cr8O 21 , it has larger specific surface area, is more conducive to the full infiltration of electrolyte and the rapid embedding and extraction of lithium ions, and has stronger discharge efficiency and electrochemical performance when applied to lithium batteries.

[0040] In the following examples, the experimental methods used are performed according to conventional or manufacturer-recommended conditions, unless otherwise specified.

[0041] The thermogravimetric analysis of CrO3 is shown in Figure 1. As can be seen from the figure, when the heating temperature is 260-270℃, CrO3 decomposes to generate the main product Cr8O 21 , and when the heating temperature exceeds 300℃, CrO3 decomposes to generate the main product Cr8O 21 , and also by-products such as Cr2O5, Cr5O 12 and Cr2O3. This result shows that when the heating temperature is controlled at 260-270℃, the generated Cr8O 21It has higher purity and fewer impurities.

[0042] Comparative Example 1

[0043] The method for preparing the positive electrode for electrochemical testing is as follows:

[0044] Take 240mg Cr8O 21 30 mg of conductive carbon black, 30 mg of polyvinylidene fluoride, and 700–800 mg of N-methylpyrrolidone were ground in an agate mortar for 15 minutes. The resulting uniformly ground slurry was then coated onto aluminum foil. The aluminum foil was placed in a vacuum drying oven and dried for 12 hours at 100°C. After drying, it was punched into round sheets with a diameter of 14 mm using a punching machine to obtain the positive electrode sheet. Cr8O 21 The SEM image is shown in Figure 2. As can be seen from the figure, Cr8O 21 It exhibits a typical sheet-like structure. The discharge volt-ampere curve of the positive electrode is shown in Figure 8.

[0045] Example 1

[0046] Grinding steps: Grind 1g of dried and pretreated CrO3 and 0.05g of FeS2 separately in a dry environment and then mix them until the color is uniform to obtain a mixture.

[0047] Heating and sintering step: The mixture is transferred to an atmospheric pressure reactor and placed in a muffle furnace for heating and reaction. Oxygen or air is introduced during the heating reaction, and the temperature is increased from room temperature to 270°C at a heating rate of 5°C / min, and held at this temperature for 18 hours. After the reaction is completed, FeS2-doped Cr8O is removed. 21 Composite cathode material. The above grinding and sintering steps are repeated multiple times to ensure complete reaction. Figure 3 shows FeS2-doped Cr8O. 21 Composite cathode materials and Cr8O 21 The XRD pattern of the standard spectrum shows that introducing FeS2 as a nucleation site can prepare Cr8O with high purity. 21 Additionally, FeS2 doped with Cr8O 21 The SEM and XRD patterns of the composite cathode material are shown in Figure 4 and Figure 7, respectively.

[0048] The preparation method of the positive electrode for electrochemical testing is the same as that of Comparative Example 1, except that Cr8O is used instead of Cr8O. 21 Replaced with FeS2-doped Cr8O 21 Composite cathode material. The discharge volt-ampere curve of the cathode is shown in Figure 8.

[0049] Example 2

[0050] Grinding step: 1 g of CrO3 and 0.1 g of FeS2 after drying pretreatment were separately ground in a dry environment and then mixed to obtain a mixture with uniform color.

[0051] Heating sintering step: the mixture was transferred to a normal pressure reaction kettle and placed in a muffle furnace for heating reaction. Oxygen or air was introduced during the heating reaction. The temperature was raised from room temperature to 260°C at a heating rate of 6°C / min, and kept constant for 12 h. After the reaction was completed, FeS2 doped Cr8O 21 composite positive electrode material. The grinding step and the heating sintering step were repeated for multiple cycles to complete the reaction. FeS2 doped Cr8O 21 The SEM image of the composite positive electrode material is shown in Fig. 5.

[0052] The preparation method of the positive electrode sheet for electrochemical test was the same as that of Comparative Example 1, except that Cr8O 21 was replaced by FeS2 doped Cr8O 21 composite positive electrode material. The discharge volt-ampere curve of the positive electrode sheet is shown in Fig. 8.

[0053] Example 3

[0054] Grinding step: 1 g of CrO3 and 0.15 g of FeS2 after drying pretreatment were separately ground in a dry environment and then mixed to obtain a mixture with uniform color.

[0055] Heating sintering step: the mixture was transferred to a normal pressure reaction kettle and placed in a muffle furnace for heating reaction. Oxygen or air was introduced during the heating reaction. The temperature was raised from room temperature to 270°C at a heating rate of 4°C / min, and kept constant for 8 h. After the reaction was completed, FeS2 doped Cr8O 21 composite positive electrode material. The grinding step and the heating sintering step were repeated for multiple cycles to complete the reaction. FeS2 doped Cr8O 21 The SEM image of the composite positive electrode material is shown in Fig. 6.

[0056] The preparation method of the positive electrode sheet for electrochemical test was the same as that of Comparative Example 1, except that Cr8O 21 was replaced by FeS2 doped Cr8O 21 composite positive electrode material. The discharge volt-ampere curve of the positive electrode sheet is shown in Fig. 8.

[0057] In Fig. 4, only the sheet-like Cr8O 21 is shown, and FeS2 is coated therein without being exposed; when FeS2 is exposed, the contrast between Cr and S will be great, and the black and white contrast of the particles in the figure will be very obvious, and it cannot be shown as the same color depth as shown in the figure. In addition, as can be seen from Figs. 4-6, with the increase of the content of FeS2 (the mass ratio of CrO3 to FeS2 is 20:1, 10:1, 6.7:1, respectively), the sheet-like Cr8O21 The spherically shaped structure of the coated FeS2 gradually changed from compact to loose, and the Cr8O 21 The particle size tended to decrease, and the particle size was in the range of 400 nm-1000 nm. When the mass ratio of CrO3 to FeS2 was lower than 10:1, the Cr8O 21 Could not completely occupy the nucleation sites of FeS2, so that the amount of Cr8O 21 attached to each FeS2 particle did not reach the optimal range. The results showed that only when the mass ratio of CrO3 to FeS2 was (10-20):1, the amount of Cr8O 21 attached to each FeS2 particle reached the optimal range, and the discharge performance of the material was better.

[0058] Comparative Example 2

[0059] Grinding step: 1 g of CrO3 and 0.2 g of FeS2 after drying pretreatment were separately ground in a dry environment and then mixed to obtain a mixture with uniform color.

[0060] Heating and sintering step: the mixture was transferred to a constant pressure reaction kettle and placed in a muffle furnace for heating reaction. Oxygen or air was introduced during the heating reaction. The temperature was increased from room temperature to 270°C at a rate of 5°C / min, and the temperature was kept constant for 12 h. After the reaction was completed, the FeS2 doped Cr8O 21 composite positive electrode material. The above grinding step and heating and sintering step were repeated several times to complete the reaction. The FeS2 doped Cr8O 21 composite positive electrode material. The XRD pattern of the composite positive electrode material is shown in Figure 7.

[0061] Figure 7 is the XRD pattern of the FeS2 doped Cr8O 21 composite positive electrode material prepared in Example 1 and Comparative Example 2, and the XRD pattern of FeS2. It can be seen that in Example 1 (mass ratio of CrO3 to FeS2 is 20:1) and Comparative Example 2 (mass ratio of CrO3 to FeS2 is 5:1), the characteristic diffraction peaks of FeS2 still exist after heating reaction, and the higher the content of FeS2, the stronger the diffraction intensity, indicating that at a heating temperature of 260-270°C, FeS2 is wrapped in the generated Cr8O 21 , and is not oxidized by the oxidizing agent (CrO3 and oxygen), and the structure is relatively stable.

[0062] The preparation method of the positive electrode sheet for electrochemical test was the same as that of Comparative Example 1, except that the Cr8O 21 was replaced by the FeS2 doped Cr8O 21 composite positive electrode material. The discharge voltammetry curve of the positive electrode sheet is shown in Figure 8.

[0063] Comparative Example 3

[0064] Grinding step: 1 g of CrO3 and 1 g of FeS2 after drying pretreatment were separately ground and mixed in a dry environment to obtain a mixture with uniform color.

[0065] Heating sintering step: the mixture was transferred to a normal pressure reaction kettle and placed in a muffle furnace for heating reaction. Oxygen or air was introduced during the heating reaction. The temperature was raised from room temperature to 270°C at a rate of 5°C / min, and the temperature was kept constant for 12 h. After the reaction was completed, FeS2 doped Cr8O 21 composite cathode material. The above grinding and heating sintering steps were repeated several times to complete the reaction.

[0066] The preparation method of the positive electrode sheet for electrochemical test is the same as that of Comparative Example 1, except that Cr8O 21 is replaced by FeS2 doped Cr8O 21 composite cathode material. The discharge volt-ampere curve of the positive electrode sheet is shown in FIG. 8.

[0067] FIG. 8 is a comparison of the discharge volt-ampere curves of Examples 1-3 and Comparative Examples 1-3. As can be seen, the discharge specific capacity of the positive electrode sheet prepared from pure Cr8O 21 is 395 mAh / g, and the discharge specific capacity of the positive electrode sheet prepared from the composite cathode material when the mass ratio of CrO3 and FeS2 is ≤5:1 is 250-300 mAh / g, which is significantly lower than that of Examples 1-3 (the discharge specific capacity is all greater than 400 mAh / g). It can be seen that when the mass ratio of CrO3 and FeS2 is (10-20):1, the FeS2 doped Cr8O 21 composite cathode material has stronger discharge efficiency and electrochemical performance when applied to lithium batteries.

[0068] Comparative Example 4

[0069] FeS2 doped Cr8O 21 The preparation method of the composite cathode material is the same as that of Example 1, except that the heating temperature of 270°C is replaced by 250°C.

[0070] The preparation method of the positive electrode sheet for electrochemical test is the same as that of Comparative Example 1, except that Cr8O 21 is replaced by FeS2 doped Cr8O 21 composite cathode material. The discharge volt-ampere curve of the positive electrode sheet is shown in FIG. 9.

[0071] Comparative Example 5

[0072] FeS2 doped Cr8O 21 The preparation method of the composite cathode material is the same as that of Example 1, except that the heating temperature of 270°C is replaced by 300°C.

[0073] The preparation method of the positive electrode sheet for electrochemical test is the same as that of Comparative Example 1, except that Cr8O21 FeS2 is replaced by Cr8O 21 The composite cathode material is used to prepare a cathode sheet.

[0074] Figure 9 is a comparison of the discharge volt-ampere curves of Example 1 and Comparative Examples 4-5, it can be seen that the discharge specific capacity of the cathode sheet prepared from the composite cathode material of Comparative Example 4 (heating temperature 250℃) and Comparative Example 5 (heating temperature 300℃) is significantly lower than that of Example 1, which indicates that when the heating temperature is 260-270℃, FeS2 doped Cr8O 21 The composite cathode material has stronger discharge efficiency and electrochemical performance when applied to a lithium battery.

[0075] Comparative Example 6

[0076] MoS2 is replaced by Cr8O 21 The preparation method of the composite cathode material is the same as that of Example 3, except that FeS2 is replaced by MoS2.

[0077] The preparation method of the cathode sheet for electrochemical test is the same as that of Comparative Example 1, except that Cr8O 21 MoS2 is replaced by Cr8O 21 The composite cathode material is used to prepare a cathode sheet.

[0078] Comparative Example 7

[0079] CoS2 is replaced by Cr8O 21 The preparation method of the composite cathode material is the same as that of Example 3, except that FeS2 is replaced by CoS2.

[0080] The preparation method of the cathode sheet for electrochemical test is the same as that of Comparative Example 1, except that Cr8O 21 CoS2 is replaced by Cr8O 21 The composite cathode material is used to prepare a cathode sheet.

[0081] Figure 10 is a comparison of the discharge volt-ampere curves of Example 1 and Comparative Examples 6-7, it can be seen that the discharge specific capacity of the cathode sheet prepared from the composite cathode material of Comparative Example 6 (doped with MoS2) and Comparative Example 7 (doped with CoS2) is less than 200 mAh / g, which is significantly lower than that of Example 1, which indicates that Cr8O 21 The composite cathode material prepared by doping FeS2 has stronger discharge efficiency and electrochemical performance when applied to a lithium battery, which has unexpected technical effects.

[0082] In summary, the FeS2 doped Cr8O 21 The composite cathode material introduces FeS2 as a nucleation site during the heating and decomposition process of CrO3, guiding the growth of Cr8O 21Crystallization on its surface, due to the uniform dispersion of FeS2, can form small-particle-size Cr8O. 21 Crystal. The FeS2-doped Cr8O prepared in this invention. 21 The composite cathode material is macroscopically presented as a powdered solid, wherein the powdered solid is a sheet-like Cr8O 21 FeS2 is coated. Meanwhile, this invention unexpectedly discovered that a heating temperature of 260–270°C limits the growth of Cr8O. 21 Continue to generate Cr2O5 and Cr5O 12 The composite cathode material prepared by removing byproducts such as Cr2O3 has the characteristics of small particle size, high purity, and few impurities. The FeS2-doped Cr8O3 prepared in this invention... 21 When composite cathode materials are used in lithium batteries, during the discharge process of the lithium battery, FeS2 doped with Cr8O 21 The composite cathode material is a powdered solid, compared to bulk Cr8O 21 With a larger specific surface area, it is more conducive to the full wetting of the electrolyte and the rapid insertion and extraction of lithium ions, thereby significantly enhancing the discharge efficiency and electrochemical performance of the battery. Meanwhile, the preparation method provided by this invention also has the advantages of simple process, controllable reaction process, and low preparation difficulty, and has good application prospects in the field of lithium batteries.

[0083] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a composite cathode material for lithium batteries, characterized in that, The method comprises: a grinding step: grinding CrO3 and FeS2 into a mixture with uniform color; Heating sintering step: the mixture is subjected to a heating reaction to obtain FeS2-doped Cr8O 21 Composite cathode material; wherein the mass ratio of CrO3 and FeS2 is (10-20):1, the heating temperature is 260-270℃, and the constant temperature time is 8-18h.

2. The method for preparing the composite cathode material for lithium batteries as described in claim 1, characterized in that, Before the grinding step, the CrO3 and FeS2 are both pretreated by drying.

3. The method for preparing the composite cathode material for lithium batteries as described in claim 1, characterized in that, The grinding step is performed in a dry environment, and the CrO3 and FeS2 are ground separately and then mixed into a mixture with uniform color.

4. The method for preparing the composite cathode material for lithium batteries as described in claim 1, characterized in that, The heating rate of the heating reaction is 4-6℃ / min.

5. The method for preparing the composite cathode material for lithium batteries as described in claim 1, characterized in that, Oxygen or air is also introduced during the heating reaction.

6. The method for preparing the composite cathode material for lithium batteries as described in claim 1, characterized in that, The method further comprises: repeatedly performing the grinding step and the heating and sintering step to complete the reaction.

7. A composite positive electrode material for lithium batteries prepared by the preparation method according to claims 1-6.

8. The composite cathode material for lithium batteries according to claim 7, characterized in that, The composite positive electrode material for lithium batteries is a powdery solid.

9. The composite cathode material for lithium batteries according to claim 8, characterized in that, The powdered solid is a flaky Cr8O 21 coated with FeS2.

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