Positive electrode lithium supplement agent and preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode lithium supplement agent and a preparation method thereof, a positive electrode pole piece and a lithium ion battery, the preparation method of the positive electrode lithium supplement agent comprises the following steps: S1, mixing a g-C3N4 nanosheet, a lithium salt and NH4HCO3 in a solvent, and then performing solid-liquid separation to obtain a g-C3N4-LiOH precursor; and S2, calcining the g-C3N4-LiOH precursor, so as to obtain the positive electrode lithium supplement agent. The positive electrode lithium supplementing agent provided by the invention can improve the first coulombic efficiency and the cycling stability of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a positive electrode lithium supplement and a preparation method thereof, a positive electrode plate and a lithium ion battery. Background Art

[0002] With the widespread popularity of mobile devices, portable electronic products and electric vehicles, lithium-ion batteries have become the mainstream choice in today's energy storage field. Due to their high energy density, long cycle life and high operating voltage, lithium-ion batteries have achieved rapid development in the past few decades. However, lithium-ion batteries often suffer from problems such as capacity decay and shortened battery life during long-term cyclic use, especially in high-rate discharge and high-temperature environments. These problems mainly come from the loss of active lithium in electrode materials and the irreversibility of side reactions. Among them, the "lithium replenishment" problem has become one of the current research hotspots. The irreversible loss of lithium leads to a decrease in battery capacity, mainly due to the formation of SEI film, side reactions between active lithium and electrolyte, and structural changes in electrode materials. Therefore, the solution of adding lithium replenishers to batteries to extend the cycle life of batteries and improve their performance by compensating for the lithium ions lost during battery cycling has received widespread attention in recent years.

[0003] In recent years, many lithium supplements have been proposed, including Li metal particles, Li3N, etc. However, these materials still have some limitations in practical applications. The high activity of Li metal easily triggers side reactions and has low safety. Although Li3N has high chemical stability, its preparation process is complicated and the cost is high. Therefore, it is of great significance to develop a new type of lithium supplement. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a positive electrode lithium replenisher and a preparation method thereof, a positive electrode plate and a lithium ion battery. The positive electrode lithium replenisher provided by the present invention can improve the initial coulombic efficiency and cycle stability of lithium ion batteries.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a positive electrode lithium supplement, the preparation method comprising the following steps:

[0007] S1, mixing g-C3N4 nanosheets, lithium salt and NH4HCO3 in a solvent, and then performing solid-liquid separation to obtain a g-C3N4-LiOH precursor;

[0008] S2. calcining the g-C3N4-LiOH precursor to obtain the positive electrode lithium supplement agent.

[0009] The positive electrode lithium supplement prepared by the invention can improve the initial coulombic efficiency and cycle stability of lithium ion batteries.

[0010] Furthermore, the preparation method of the g-C3N4 nanosheets comprises the following steps:

[0011] Urea is added into a covered crucible, and after the first calcination and cooling, the cover of the crucible is removed and the second calcination is performed to obtain the g-C3N4 nanosheets.

[0012] Furthermore, in the preparation process of the g-C3N4 nanosheets, the atmosphere of the first calcination is an air atmosphere, the heating rate of the first calcination is 5 to 10°C / min, and the temperature of the first calcination is 550 to 650°C; the atmosphere of the second calcination is an air atmosphere, the heating rate of the second calcination is 1 to 10°C / min, and the temperature of the second calcination is 500 to 600°C.

[0013] Further, in step S1, the lithium salt includes LiCl;

[0014] And / or, in step S1, the molar ratio of lithium element in the lithium salt to the NH4HCO3 is (0.3-1.5):3;

[0015] and / or, in step S1, the solvent comprises anhydrous ethanol;

[0016] And / or, in step S1, the mixing time is 6 to 10 hours;

[0017] And / or, in step S1, after solid-liquid separation, the solid is washed with ethanol and water for multiple times and then dried, wherein the drying temperature is 40-60°C.

[0018] Furthermore, in step S2, the calcination atmosphere includes one of an oxygen atmosphere and an air atmosphere, the calcination heating rate is 5-10°C / min, and the calcination temperature is 300-400°C.

[0019] In a second aspect, the present invention provides a positive electrode lithium replenisher, which is prepared by the preparation method described in the first aspect, and the positive electrode lithium replenisher includes g-C3N4 and lithium loaded on the g-C3N4.

[0020] Furthermore, the ratio of the mass of the g-C3N4 to the amount of the lithium substance loaded on the g-C3N4 is 900: (0.3-1.5) mg / mmol.

[0021] In a third aspect, the present invention provides a positive electrode plate, which includes an active material and a positive electrode lithium replenisher; wherein the positive electrode lithium replenisher includes the positive electrode lithium replenisher described in the second aspect or the positive electrode lithium replenisher prepared by the preparation method described in the first aspect.

[0022] Furthermore, the positive electrode plate also includes a conductive agent and a binder, wherein the mass ratio of the active material, the conductive agent, the binder and the positive electrode lithium replenisher is (90-97): (1-5): (1-5): (0.5-3).

[0023] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the positive electrode sheet described in the third aspect.

[0024] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0025] (1) The positive electrode lithium supplement provided by the present invention can improve the initial coulombic efficiency and cycle stability of lithium-ion batteries.

[0026] (2) g-C3N4-Li lithium supplement can replenish the lithium lost in the negative electrode during the first charge process, thereby improving the first charge and discharge efficiency of the battery. Compared with traditional lithium supplements, g-C3N4-Li lithium supplement has better lithium supplement effect and higher efficiency.

[0027] (3) The g-C3N4-Li lithium supplement can stably exist in the battery, continuously replenishing the lithium lost by the negative electrode, and further enhancing the cycle stability of the battery.

[0028] (4) As an inorganic non-metallic material, g-C3N4 has good thermal and chemical stability, which can improve the safety performance of the battery. At the same time, the preparation process of g-C3N4-Li lithium supplement avoids the use of flammable and explosive materials such as metallic lithium powder, reducing the safety risk of the battery.

[0029] (5) The raw materials of g-C3N4 are widely available and relatively cheap, which helps to reduce the cost of lithium-ion batteries. At the same time, the preparation process of g-C3N4-Li lithium supplement is simple and easy to scale up, further reducing the production cost of batteries.

[0030] (6) The method of using g-C3N4 combined with Li as a lithium supplement in lithium-ion batteries improves battery performance and reduces costs, which helps promote the widespread application of lithium-ion batteries in electric vehicles, energy storage systems and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a SEM image of the positive electrode lithium supplement prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0034] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0035] In a first aspect, the present invention provides a method for preparing a positive electrode lithium supplement, the preparation method comprising the following steps:

[0036] S1, mixing g-C3N4 nanosheets, lithium salt and NH4HCO3 in a solvent, and then performing solid-liquid separation to obtain a g-C3N4-LiOH precursor;

[0037] S2. Calcine the g-C3N4-LiOH precursor to obtain the positive electrode lithium supplement (g-C3N4-Li).

[0038] The role of NH4HCO3 in the present invention is: (1) Providing a nitrogen source: containing nitrogen, it may participate in the reaction as a nitrogen source in the subsequent reaction process. During the thermal calcination process, nitrogen can react chemically with other elements (such as carbon, etc.), which helps to form the nitrogen-containing structure of the target product. For example, it may interact with CNNSs and other additives, so that nitrogen atoms are embedded in the lattice structure of the product or form nitrogen-containing functional groups during high-temperature calcination, thereby changing the chemical composition and properties of the product. (2) Producing gas-assisted reactions: It is easy to decompose when heated to produce ammonia, carbon dioxide and water. The generation of these gases plays an important role in the reaction process. On the one hand, the escape of gas may cause a microscopic "stirring" effect in the reaction system, which helps to mix and contact between the raw materials and make the reaction more complete. On the other hand, the generated gas may participate in the morphology control of the product, for example, by adjusting the internal pressure and material transfer process, affecting the pore structure formation of the product or the degree of agglomeration of the particles, thereby obtaining a product with a specific microstructure. (3) Adjusting the pH value of the reaction system: NH4HCO3 is a weak acid and weak base salt that undergoes hydrolysis in solution. The ions produced by its hydrolysis can adjust the pH value of the reaction system. Appropriate pH has an important influence on the dissolution, precipitation, and polymerization of substances during the reaction. For example, it may affect the charge state of the CNNSs surface, allowing CNNSs to be better dispersed in the solution and avoid agglomeration. At the same time, a suitable pH environment is conducive to the dissolution of lithium salts and subsequent reactions with other substances, ensuring that the reaction can proceed smoothly in a suitable chemical environment.

[0039] The positive electrode lithium supplement prepared by the invention can improve the initial coulombic efficiency and cycle stability of lithium ion batteries.

[0040] In the above-mentioned method for preparing the positive electrode lithium supplement, as an optional embodiment, the method for preparing the g-C3N4 nanosheets comprises the following steps:

[0041] Urea is added into a covered crucible, and after the first calcination and cooling, the cover of the crucible is removed and the second calcination is performed to obtain the g-C3N4 nanosheets.

[0042] The present invention prepares g-C3N4 into nanosheets, introduces lithium elements and forms a g-C3N4-Li composite material, which not only improves the binding ability of g-C3N4 with lithium, but also maintains its structural stability and electronic conductivity. This is a key step in realizing the application of g-C3N4 as a lithium supplement in lithium-ion batteries.

[0043] In this embodiment, the functions of the lid during the first calcination are: (1) Controlling the atmosphere and the degree of reaction: Urea will undergo a series of chemical reactions such as decomposition and polycondensation during the heating process. Covering the lid helps to maintain a relatively closed air atmosphere inside the crucible, so that the gas and other substances produced by the decomposition of urea can participate in the reaction in a relatively limited space, which is conducive to the formation of some precursor substances in the initial stage and the orderly conduct of the initial polymerization reaction, and avoids excessive interference from the outside air, which may lead to disordered reaction process or the generation of some undesirable by-products. (2) Temperature uniformity and stability: The lid can reduce the rapid loss of heat, help the temperature inside the crucible to rise more evenly and remain stable, so that the materials in the entire crucible can react relatively synchronously and fully under the set temperature conditions, so that the reaction degree of each part of the material is relatively consistent, and ensure that the product obtained by the first calcination has the expected chemical composition and structural characteristics.

[0044] The purpose of removing the lid during the second calcination is: (1) Adjusting the reaction atmosphere and deep oxidation: After the first step of the reaction, a specific intermediate product (yellow product) has been generated. Removing the lid allows more air to enter the crucible, increasing the contact between oxygen and the intermediate product, promoting further oxidation reactions and structural rearrangement, and helping to transform the intermediate product into the target product, ultra-thin CNNSs, making the product structure more perfect and its performance more in line with the requirements. (2) Changing the atmosphere conditions to drive some subsequent reaction steps that need to occur in a relatively oxygen-rich environment, such as modifying the structure of carbon, nitrogen and other elements formed in the early stage, removing some residual small molecular impurities, etc., and obtaining purer and more ideal light yellow CNNSs through a sufficient oxidation process. (3) Different stages have different requirements for temperature, atmosphere and other conditions. The environmental changes after removing the lid can be combined with new heating conditions and other factors to fine-tune the key performance indicators of the product, such as crystallinity and specific surface area, so that the final CNNSs have better application potential.

[0045] In the above-mentioned method for preparing the positive electrode lithium supplement, as an optional embodiment, in the preparation process of the g-C3N4 nanosheet, the atmosphere of the first calcination is an air atmosphere, the heating rate of the first calcination is 5 to 10°C / min, for example, it can be 5°C / min, 7°C / min or 10°C / min, the temperature of the first calcination is 550 to 650°C, for example, it can be 550°C, 600°C or 650°C, the atmosphere of the second calcination is an air atmosphere, the heating rate of the second calcination is 1 to 10°C / min, for example, it can be 1°C / min, 5°C / min, 7°C / min or 10°C / min, and the temperature of the second calcination is 500 to 600°C, for example, it can be 500°C, 550°C or 600°C.

[0046] In the above-mentioned method for preparing a positive electrode lithium supplement, as an optional implementation, in step S1, the lithium salt includes LiCl.

[0047] In the above-mentioned method for preparing the positive electrode lithium supplement, as an optional implementation, in step S1, the molar ratio of the lithium element in the lithium salt to the NH4HCO3 is (0.3-1.5):3.

[0048] In the above-mentioned method for preparing a positive electrode lithium supplement, as an optional implementation, in step S1, the solvent includes anhydrous ethanol.

[0049] In the above-mentioned method for preparing the positive electrode lithium supplement, as an optional implementation, in step S1, the mixing time is 6 to 10 hours, for example, 6 hours, 8 hours or 10 hours.

[0050] In the above-mentioned method for preparing a positive electrode lithium supplement, as an optional implementation, in step S1, after solid-liquid separation, the solid is washed multiple times with ethanol and water and then dried, wherein the drying temperature is 40 to 60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0051] In the above-mentioned method for preparing a positive electrode lithium supplement, as an optional embodiment, in step S2, the calcination atmosphere includes one of an oxygen atmosphere and an air atmosphere, the calcination heating rate is 5 to 10°C / min, for example, it can be 5°C / min, 7°C / min or 10°C / min, and the calcination temperature is 300 to 400°C, for example, it can be 300°C, 320°C, 340°C, 360°C, 380°C or 400°C.

[0052] In a second aspect, the present invention provides a positive electrode lithium replenisher, which is prepared by the preparation method described in the first aspect, and the positive electrode lithium replenisher includes g-C3N4 and lithium loaded on the g-C3N4.

[0053] g-C3N4-Li lithium supplementer exhibits a unique lithium supplementation mechanism in lithium-ion batteries. During the first charge process, g-C3N4-Li lithium supplementer can supplement the lithium lost in the negative electrode, thereby improving the first charge and discharge efficiency of the battery. At the same time, during the cycle process, g-C3N4-Li lithium supplementer can stably exist in the battery, continuously supplement the lithium lost in the negative electrode, and enhance the cycle stability of the battery.

[0054] In the above-mentioned positive electrode lithium supplement, as an optional embodiment, the ratio of the mass of the g-C3N4 to the amount of the lithium substance loaded on the g-C3N4 is 900: (0.3-1.5) mg / mmol.

[0055] In a third aspect, the present invention provides a positive electrode plate, which includes an active material and a positive electrode lithium replenisher; wherein the positive electrode lithium replenisher includes the positive electrode lithium replenisher described in the second aspect or the positive electrode lithium replenisher prepared by the preparation method described in the first aspect.

[0056] In the above-mentioned positive electrode plate, as an optional implementation, the positive electrode plate also includes a conductive agent and a binder.

[0057] In the above-mentioned positive electrode plate, as an optional implementation, the active material includes lithium iron phosphate.

[0058] In the above-mentioned positive electrode plate, as an optional implementation, the conductive agent includes conductive carbon black.

[0059] In the above-mentioned positive electrode plate, as an optional implementation, the binder includes polyvinylidene fluoride.

[0060] In the above-mentioned positive electrode sheet, as an optional embodiment, the mass ratio of the active material, the conductive agent, the binder and the positive electrode lithium supplement is (90-97): (1-5): (1-5): (0.5-3). In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0061] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0062] Example 1

[0063] The present invention provides a method for preparing a positive electrode lithium supplement agent based on g-C3N4, the preparation method comprising the following steps:

[0064] 1. Preparation of g-C3N4 nanosheets:

[0065] g-C3N4 was synthesized by a two-step thermal polymerization method. The specific steps are as follows: a certain amount of urea was added to a covered crucible, and calcined at 600°C for 4 hours at a temperature increase of 5°C / min in a muffle furnace air atmosphere, and a yellow product was obtained after natural cooling to room temperature, and then the lid of the crucible was removed, and calcined at 550°C for 2 hours at a temperature increase of 2.5°C / min, and finally light yellow g-C3N4 was obtained after natural cooling.

[0066] 2. Preparation of lithium supplement:

[0067] First, weigh 900 mg of g-C3N4 prepared in step 1, add it to 90 mL of anhydrous ethanol, and disperse it with ultrasound assistance for 1.5 hours to obtain a g-C3N4 suspension, then add 1 mmol LiCl and dissolve it in the above g-C3N4 suspension. Then add 3 mmol NH4HCO3 and continue stirring at room temperature for 8 hours. The g-C3N4-LiOH precursor was obtained by centrifugal collection, then washed three times with ethanol, then washed three times with distilled water, and dried in an oven at 40°C overnight. Finally, the dried precursor was calcined at 350°C for 2 hours in a tubular furnace under an air atmosphere with a heating condition of 5°C / min, and a positive electrode lithium supplement (g-C3N4-Li) based on g-C3N4 was obtained after natural cooling.

[0068]

[0069] In g-C3N4-Li, Li is captured by N in g-C3N4 and fixed in g-C3N4.

[0070] Figure 1 This is a SEM image of the positive electrode lithium supplement prepared in the embodiment of the present invention. Figure 1 It can be seen that the lithium supplement prepared in this example is in the form of flakes without obvious particles.

[0071] Example 2

[0072] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this embodiment is basically the same as that in Example 1, except that in step 2, the amount of LiCl used is 0.5 mmol.

[0073] Example 3

[0074] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this embodiment is basically the same as that in Example 1, except that in step 2, the amount of LiCl used is 0.8 mmol.

[0075] Example 4

[0076] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this embodiment is basically the same as that in Example 1, except that in step 2, the amount of LiCl used is 1.2 mmol.

[0077] Example 5

[0078] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this embodiment is basically the same as that in Example 1, except that in step 2, the amount of LiCl used is 1.5 mmol.

[0079] Example 6

[0080] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this embodiment is basically the same as that in Example 1, the difference is that in step 1, the heating rate of the first calcination is 7°C / min, the heating rate of the second calcination is 5°C / min, and in step 2, the heating rate of calcination is 7.5°C / min.

[0081] Comparative Example 1

[0082] The lithium supplement provided in this comparative example is Li5FeO4.

[0083] Comparative Example 2

[0084] The lithium supplement provided in this comparative example is Li3N.

[0085] Comparative Example 3

[0086] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this comparative example is basically the same as that in Example 1, except that in step 2, NH4HCO3 is not added.

[0087] Comparative Example 4

[0088] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this comparative example is basically the same as that in Example 1, except that in step 1, the lid of the crucible is not removed during the second calcination.

[0089] Comparative Example 5

[0090] The preparation method of the positive electrode lithium supplement agent based on g-C3N4 provided in this comparative example is basically the same as that in Example 1, except that in step 2, the calcination atmosphere is an argon atmosphere.

[0091] Performance Testing

[0092] The lithium supplement prepared in each embodiment and comparative example is applied to the positive electrode sheet, and then assembled into a lithium ion battery. The specific production method is as follows:

[0093] Lithium iron phosphate, SP conductive agent, PVDF and the lithium supplement agent prepared in the embodiment or the comparative example are mixed in a mass ratio of 97:1:1.5:0.5 to prepare a positive electrode slurry, and each positive electrode slurry is evenly coated on a carbon-coated aluminum foil by a transfer coater to obtain a positive electrode plate; the above-mentioned positive electrode plates are assembled with an electrolyte, a separator and a graphite negative electrode plate according to a conventional method to obtain a lithium-ion battery.

[0094] Blank control group: lithium iron phosphate, SP conductive agent and PVDF were mixed in a mass ratio of 97.5:1:1.5 to prepare a positive electrode slurry, and the positive electrode slurry was evenly coated on a carbon-coated aluminum foil by a transfer coater to obtain a positive electrode plate; the positive electrode plate was assembled with an electrolyte, a separator and a graphite negative electrode plate according to a conventional method to obtain a lithium-ion battery.

[0095] The assembled lithium-ion battery was subjected to charge and discharge cycle tests to evaluate its initial coulombic efficiency and cycle stability. The test results are shown in Table 1. The specific test method is as follows:

[0096] The first coulombic efficiency = the total charging capacity of the formation step (2, 4, 6) + the capacity division step (2) / the discharge capacity of the capacity division step (4) * 100%, that is, the first coulombic efficiency = the first charging capacity / the first discharge capacity * 100%: Formation step: (1) stand for 1 min; (2) 0.02C CC (constant current) charging for 30 min; (3) stand for 1 min; (4) 0.1C CC (constant current) charging for 48 min; (5) stand for 1 min; (6) 0.33C CC (constant current) charging for 62 min; (7) stand for 5 min; (8) end; capacity division step: (1) stand for 1 min; (2) 0.5C CCCV (constant current constant voltage) charging for 300 min, with a cut-off voltage of 3.65 V; (3) stand for 15 min; (4) 0.33C CC (constant current) discharge for 210 min, with a cut-off voltage of 2.5 V; (5) stand for 15 min.

[0097] Charge and discharge cycle life test: (1) Place at 25℃±2℃ for 120min; (2) Charge at 1 / 3CCCV (constant current constant voltage) to 3.65V, cut-off current 0.05C; (3) Charge at 1 / 3C CC (constant current) discharge to 2.5V, (4) stand for 30min (5) cycle 2-4 steps for two weeks, (6) 1 / 3C constant current constant voltage charge to 3.65V, cut-off current 0.05C, (7) stand for 30min; (8) 1 / 3C constant current discharge to 2.5V, (9) stand for 30min; (record the capacity as C0, the capacity is corrected every 100 cycles); (10) 1C0 constant current constant voltage charge to 3.65V, cut-off current 0.05C0; stand for 30min; 11) 1C0 constant current discharge to 2.5V; stand for 30min; (12) repeat steps 10-11 for 100 cycles, (13) stand for 24h, (14) repeat steps 6-13 until 500 cycles are stopped, the 500th cycle charging capacity / 1st cycle charging capacity is the 500-cycle cycle capacity retention rate.

[0098] Table 1

[0099]

[0100] From Table 1, we can see at least the following points:

[0101] (1) By comparing Examples 1-6 with the blank control group, it can be seen that the positive electrode lithium supplement provided by the present invention can improve the initial coulombic efficiency and cycle stability of lithium-ion batteries.

[0102] (2) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that compared with the conventional lithium supplement in the prior art, when the same amount of lithium supplement is used, the lithium supplement provided by the present invention has a better lithium supplement effect.

[0103] (3) By comparing Example 1 with Comparative Example 3, it can be seen that when NH4HCO3 is not added in step 2, the first coulombic efficiency and cycle stability both decrease.

[0104] (4) By comparing Example 1 with Comparative Example 4, it can be seen that when the crucible lid is not removed during the second calcination, the first coulombic efficiency and cycle stability both decrease.

[0105] (5) By comparing Example 1 with Comparative Example 5, it can be seen that when the calcination atmosphere in step 2 is an argon atmosphere, the first coulombic efficiency and cycle stability both decrease.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode lithium supplement, characterized in that: The preparation method comprises the following steps: S1, mixing g-C3N4 nanosheets, lithium salt and NH4HCO3 in a solvent, and then performing solid-liquid separation to obtain a g-C3N4-LiOH precursor; S2. calcining the g-C3N4-LiOH precursor to obtain the positive electrode lithium supplement agent.

2. The method for preparing a positive electrode lithium supplement according to claim 1, characterized in that: The preparation method of the g-C3N4 nanosheets comprises the following steps: Urea is added into a covered crucible, and after the first calcination and cooling, the cover of the crucible is removed and the second calcination is performed to obtain the g-C3N4 nanosheets.

3. The method for preparing a positive electrode lithium supplement according to claim 2, characterized in that: During the preparation process of the g-C3N4 nanosheets, the atmosphere of the first calcination is an air atmosphere, the heating rate of the first calcination is 5-10°C / min, the temperature of the first calcination is 550-650°C, the atmosphere of the second calcination is an air atmosphere, the heating rate of the second calcination is 1-10°C / min, and the temperature of the second calcination is 500-600°C.

4. The method for preparing a positive electrode lithium supplement according to claim 1, characterized in that: In step S1, the lithium salt includes LiCl; And / or, in step S1, the molar ratio of lithium element in the lithium salt to the NH4HCO3 is (0.3-1.5):3; and / or, in step S1, the solvent comprises anhydrous ethanol; And / or, in step S1, the mixing time is 6 to 10 hours; And / or, in step S1, after solid-liquid separation, the solid is washed with ethanol and water for multiple times and then dried, wherein the drying temperature is 40-60°C.

5. The method for preparing a positive electrode lithium supplement according to claim 1, characterized in that: In step S2, the calcination atmosphere includes one of an oxygen atmosphere and an air atmosphere, the calcination heating rate is 5-10°C / min, and the calcination temperature is 300-400°C.

6. A positive electrode lithium supplement, characterized in that: The positive electrode lithium replenisher is prepared by the preparation method described in any one of claims 1 to 5, and the positive electrode lithium replenisher includes g-C3N4 and lithium loaded on the g-C3N4.

7. The positive electrode lithium supplement according to claim 6, characterized in that: The ratio of the mass of the g-C3N4 to the amount of the lithium substance supported on the g-C3N4 is 900: (0.3-1.5) mg / mmol.

8. A positive electrode sheet, characterized in that: The positive electrode plate comprises an active material and a positive electrode lithium replenisher; wherein the positive electrode lithium replenisher comprises the positive electrode lithium replenisher according to claim 6 or 7 or the positive electrode lithium replenisher prepared by the preparation method according to any one of claims 1 to 5.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode plate also includes a conductive agent and a binder, wherein the mass ratio of the active material, the conductive agent, the binder and the positive electrode lithium supplement is (90-97): (1-5): (1-5): (0.5-3).

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 8 or 9.

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