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

Abstract

This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishing agent and its preparation method, a positive electrode sheet, and a lithium-ion battery. The preparation method of the positive electrode lithium replenishing agent includes the following steps: S1, mixing g-C3N4 nanosheets, lithium salt, and NH4HCO3 in a solvent, followed by solid-liquid separation to obtain a g-C3N4-LiOH precursor; S2, calcining the g-C3N4-LiOH precursor to obtain the positive electrode lithium replenishing agent. The positive electrode lithium replenishing agent provided by this invention can improve the initial coulombic efficiency and cycle stability of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium replenishing agent and its preparation method, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] With the widespread adoption of mobile devices, portable electronic products, and electric vehicles, lithium-ion batteries have become the mainstream choice in the energy storage field. Due to their high energy density, long cycle life, and high operating voltage, lithium-ion batteries have experienced rapid development over the past few decades. However, during long-term cycling, especially in high-rate discharge and high-temperature environments, lithium-ion batteries often suffer from capacity decay and shortened battery life. These problems mainly stem from the loss of active lithium in the electrode materials and the irreversibility of side reactions, with "lithium replenishment" becoming a current research hotspot. Irreversible lithium loss leads to a decrease in battery capacity, primarily due to factors including SEI film formation, side reactions between active lithium and the electrolyte, and structural changes in electrode materials. Therefore, the addition of lithium replenishing agents to the battery to compensate for the lithium ions lost during cycling, thereby extending the battery's cycle life and improving its performance, has received widespread attention in recent years.

[0003] In recent years, many lithium supplements have been proposed, including Li metal particles and Li3N. However, these materials still have some limitations in practical applications. The high reactivity of Li metal easily triggers side reactions, resulting in low safety. Although Li3N has high chemical stability, its preparation process is complex and costly. Therefore, developing a novel lithium supplement is of great significance. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the purpose of this invention is to provide a positive electrode lithium replenishing agent and its preparation method, a positive electrode sheet and a lithium-ion battery. The positive electrode lithium replenishing agent provided by this invention can improve the initial coulombic efficiency and cycle stability of lithium-ion batteries.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

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

[0007] S1. G-C3N4 nanosheets, lithium salt and NH4HCO3 are mixed in a solvent and then separated by solid-liquid separation to obtain g-C3N4-LiOH precursor;

[0008] S2. The g-C3N4-LiOH precursor is calcined to obtain the positive electrode lithium replenishing agent.

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

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

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

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

[0013] Furthermore, 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 NH4HCO3 is (0.3~1.5):3;

[0015] And / or, in step S1, the solvent includes 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 multiple times with ethanol and water and then dried, wherein the drying temperature is 40-60°C.

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

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

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

[0021] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising an active material and a positive electrode lithium replenishing agent; wherein the positive electrode lithium replenishing agent comprises the positive electrode lithium replenishing agent described in the second aspect or the positive electrode lithium replenishing agent prepared by the preparation method described in the first aspect.

[0022] Furthermore, the positive electrode sheet 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).

[0023] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising 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 replenishing agent provided by the present invention can improve the initial coulombic efficiency and cycle stability of lithium-ion batteries.

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

[0027] (3) g-C3N4-Li lithium replenisher can exist stably in the battery, continuously replenish the lithium lost by the negative electrode, and further enhance 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, thus reducing the safety risks of the battery.

[0029] (5) g-C3N4 has a wide range of raw material sources and a relatively low price, 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, which further reduces the production cost of batteries.

[0030] (6) The method of combining g-C3N4 with Li as a lithium replenishing agent in lithium-ion batteries of the present invention improves the performance of the battery and reduces the cost, which helps to promote the widespread application of lithium-ion batteries in electric vehicles, energy storage systems and other fields. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a SEM image of the positive electrode lithium replenishing agent prepared in Example 1 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0034] The endpoints and any values ​​of the ranges disclosed in this 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

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

[0036] S1. G-C3N4 nanosheets, lithium salt and NH4HCO3 are mixed in a solvent and then separated by solid-liquid separation to obtain g-C3N4-LiOH precursor;

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

[0038] The role of NH4HCO3 in this invention is as follows: (1) Providing a nitrogen source: It contains nitrogen and may participate in the reaction as a nitrogen source in subsequent reaction processes. During the hot calcination process, nitrogen can react chemically with other elements (such as carbon), which helps to form the nitrogen-containing structural part of the target product. For example, it may interact with CNNSs and other additives, causing nitrogen atoms to embed into the crystal 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) Generating gases to assist the reaction: It is easily decomposed by heat, producing 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 the gases may create a microscopic "stirring" effect in the reaction system, which helps to mix and contact the raw materials, making the reaction more complete. On the other hand, the generated gases may participate in the morphology control of the product, for example, by adjusting the internal pressure and mass transport process, affecting the formation of the pore structure of the product or the degree of particle aggregation, thereby obtaining a product with a specific microstructure. (3) Adjusting the pH of the reaction system: NH4HCO3 is a weak acid-weak base salt that undergoes hydrolysis in solution. The ions produced by its hydrolysis can adjust the pH of the reaction system. A suitable pH has a significant impact on processes such as dissolution, precipitation, and polymerization during the reaction. For example, it may affect the charge state of the CNNS surface, allowing CNNS to be better dispersed in solution and preventing aggregation. Simultaneously, a suitable pH environment is beneficial for the dissolution of lithium salts and subsequent reactions with other substances, ensuring that the reaction proceeds smoothly in a suitable chemical environment.

[0039] The positive electrode lithium replenishing agent prepared by this 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 includes the following steps:

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

[0042] This invention prepares g-C3N4 into nanosheets, introduces lithium, and forms a g-C3N4-Li composite material. This 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 function of covering the crucible during the first calcination is: (1) Controlling the atmosphere and reaction degree: Urea undergoes a series of chemical reactions such as decomposition and condensation during heating. Covering the crucible helps to maintain a relatively closed air atmosphere inside the crucible, allowing the gases and other substances produced by the decomposition of urea to participate in the reaction in a relatively limited space. This is beneficial for the formation of some precursor substances in the initial stage and for the orderly progress of the initial polymerization reaction, avoiding excessive interference from the outside air, which could lead to disorder in the reaction process or the generation of some undesirable byproducts. (2) Temperature uniformity and stability: The lid can reduce the rapid loss of heat, which helps the temperature inside the crucible to rise more uniformly and remain stable. This allows the materials in the entire crucible to react more synchronously and fully under the set temperature conditions, making the reaction degree of each part of the material relatively consistent, and ensuring that the product obtained from the first calcination has the expected chemical composition and structural characteristics.

[0044] The purpose of removing the lid during the second calcination is: (1) to adjust 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, which helps to transform the intermediate product into the target product, ultrathin CNNSs, making the product structure more perfect and its performance more in line with requirements. (2) to change the atmosphere conditions to drive some subsequent reaction steps that need to occur in a relatively oxygen-rich environment, such as modifying the structure containing carbon, nitrogen and other elements formed in the early stage, removing some residual small molecule impurities, etc., and obtaining purer and more ideal light yellow CNNSs through a full 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 finely adjust the key performance indicators such as crystallinity and specific surface area of ​​the product, 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, during the preparation of the g-C3N4 nanosheets, the atmosphere for the first calcination is an air atmosphere, the heating rate for the first calcination is 5-10℃ / min, for example, 5℃ / min, 7℃ / min or 10℃ / min, the temperature for the first calcination is 550-650℃, for example, 550℃, 600℃ or 650℃, the atmosphere for the second calcination is an air atmosphere, the heating rate for the second calcination is 1-10℃ / min, for example, 1℃ / min, 5℃ / min, 7℃ / min or 10℃ / min, the temperature for the second calcination is 500-600℃, for example, 500℃, 550℃ or 600℃.

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

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

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

[0049] In the above-mentioned method for preparing positive electrode lithium replenishing agent, as an optional embodiment, 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 positive electrode lithium supplement, as an optional embodiment, in step S1, after solid-liquid separation, the solid is washed multiple times with ethanol and water and then dried. The drying temperature is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0051] In the above-mentioned method for preparing the 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 5-10℃ / min, for example, 5℃ / min, 7℃ / min or 10℃ / min, and the calcination temperature is 300-400℃, for example, 300℃, 320℃, 340℃, 360℃, 380℃ or 400℃.

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

[0053] g-C3N4-Li lithium replenisher exhibits a unique lithium replenishment mechanism in lithium-ion batteries. During the initial charge, g-C3N4-Li replenishes lithium lost from the negative electrode, thereby improving the battery's initial charge-discharge efficiency. Simultaneously, during cycling, g-C3N4-Li remains stable within the battery, continuously replenishing lithium lost from the negative electrode and enhancing the battery's cycle stability.

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

[0055] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising an active material and a positive electrode lithium replenishing agent; wherein the positive electrode lithium replenishing agent comprises the positive electrode lithium replenishing agent described in the second aspect or the positive electrode lithium replenishing agent prepared by the preparation method described in the first aspect.

[0056] In one optional embodiment, the positive electrode sheet described above further includes a conductive agent and a binder.

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

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

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

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

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

[0062] Example 1

[0063] This invention provides a method for preparing a positive electrode lithium supplement 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℃ for 4 hours in an air atmosphere in a muffle furnace with a heating rate of 5℃ / min. After natural cooling to room temperature, a yellow product was obtained. Then, the lid of the crucible was removed, and calcined at 550℃ for 2 hours with a heating rate of 2.5℃ / min. Finally, after natural cooling, light yellow g-C3N4 was obtained.

[0066] 2. Preparation of lithium supplement:

[0067] First, 900 mg of the g-C3N4 prepared in step 1 was weighed and added to 90 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 1.5 h to obtain a g-C3N4 suspension. Then, 1 mmol of LiCl was added and dissolved in the g-C3N4 suspension. Next, 3 mmol of NH4HCO3 was added, and the mixture was stirred continuously at room temperature for 8 h. The g-C3N4-LiOH precursor was collected by centrifugation, washed three times with ethanol, then three times with distilled water, and dried overnight in an oven at 40 °C. Finally, the dried precursor was calcined in a tube furnace under air atmosphere at a heating rate of 5 °C / min at 350 °C for 2 h. After natural cooling, a g-C3N4-based positive electrode lithium supplement (g-C3N4-Li) was obtained.

[0068]

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

[0070] Figure 1 The image shown is a SEM image of the positive electrode lithium replenishment agent prepared according to an embodiment of the present invention. Figure 1 As can be seen, the lithium supplement prepared in this embodiment is in the form of flakes and has no obvious particles.

[0071] Example 2

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

[0073] Example 3

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

[0075] Example 4

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

[0077] Example 5

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

[0079] Example 6

[0080] The preparation method of the positive electrode lithium supplement 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℃ / min, the heating rate of the second calcination is 5℃ / min, and in step 2, the heating rate of the calcination is 7.5℃ / 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 replenishing agent based on g-C3N4 provided in this comparative example is basically the same as that in Example 1, except that NH4HCO3 is not added in step 2.

[0087] Comparative Example 4

[0088] The preparation method of the positive electrode lithium replenishing 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 replenishing agent based on g-C3N4 provided in this comparative example is basically the same as that in Example 1, except that the calcination atmosphere in step 2 is argon atmosphere.

[0091] Performance testing

[0092] The lithium replenishing agents prepared in each embodiment and comparative example are applied to the positive electrode sheet and then assembled into a lithium-ion battery. The specific manufacturing method is as follows:

[0093] Lithium iron phosphate, SP conductive agent, PVDF, and lithium supplementing agent prepared in the examples or comparative examples were mixed in a mass ratio of 97:1:1.5:0.5 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto carbon-coated aluminum foil using a transfer coating machine to obtain a positive electrode sheet. The above positive electrode sheets were assembled with electrolyte, separator, and graphite negative electrode sheet according to conventional methods to obtain a lithium-ion battery.

[0094] Blank control group: Lithium iron phosphate, SP conductive agent and PVDF were mixed at a mass ratio of 97.5:1:1.5 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on carbon-coated aluminum foil using a transfer coating machine to obtain a positive electrode sheet. The above positive electrode sheet was assembled with electrolyte, separator and graphite negative electrode sheet according to conventional methods to obtain a lithium-ion battery.

[0095] The assembled lithium-ion batteries were subjected to charge-discharge cycle tests to evaluate their initial coulombic efficiency and cycle stability. The test results are shown in Table 1. The specific test methods are as follows:

[0096] First Coulomb efficiency = Formation step (2, 4, 6) + Capacitance grading step (2) total charging capacity / Capacitance grading step (4) discharge capacity * 100%, that is, first Coulomb efficiency = first charging capacity / first discharging capacity * 100%: Formation step: (1) rest for 1 min; (2) 0.02C CC (constant current) charging for 30 min; (3) rest for 1 min; (4) 0.1C CC (constant current) charging for 48 min; (5) rest for 1 min; (6) 0.33C CC (constant current) charging for 62 min; (7) rest for 5 min; (8) end; Capacitance grading step: (1) rest for 1 min; (2) 0.5C CCCV (constant current and constant voltage) charging for 300 min, cutoff voltage is 3.65V; (3) rest for 15 min; (4) 0.33C CC (constant current) discharging for 210 min, cutoff voltage is 2.5V; (5) rest for 15 min.

[0097] Charge-discharge cycle life test: (1) rest at 25℃±2℃ for 120min; (2) charge to 3.65V with 1 / 3CCCCV (constant current and constant voltage) and cut-off current of 0.05C; (3) charge at 1 / 3C (4) Discharge CC (constant current) to 2.5V, (5) Let stand for 30 minutes, (6) Repeat steps 2-4 for two weeks, (7) Charge 1 / 3C constant current and constant voltage to 3.65V, cut-off current 0.05C, (8) Let stand for 30 minutes; (9) Discharge 1 / 3C constant current to 2.5V, (10) Let stand for 30 minutes; (11) Record the capacity as C0, and the capacity is corrected every 100 cycles); (12) Charge 1C0 constant current and constant voltage to 3.65V, cut-off current 0.05C0; let stand for 30 minutes; (13) Discharge 1C0 constant current to 2.5V; let stand for 30 minutes; (14) Repeat steps 10-11 for 100 cycles, (15) Let stand for 24 hours, (16) Repeat steps 6-13 until 500 cycles are completed and the capacity of the 500th cycle / the capacity of the 1st cycle is the capacity retention rate of the 500 cycles.

[0098] Table 1

[0099]

[0100] At least the following points can be observed from Table 1:

[0101] (1) Comparison of Examples 1-6 with the blank control group shows that the positive electrode lithium replenishment agent provided by the present invention can improve the first coulombic efficiency and cycle stability of lithium-ion batteries.

[0102] (2) Comparing Example 1 with Comparative Example 1 and Comparative Example 2, it can be seen that, compared with conventional lithium replenishing agents in the prior art, the lithium replenishing agent provided by the present invention has a better lithium replenishing effect when using the same amount of lithium replenishing agent.

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

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

[0105] (5) Comparing Example 1 with Comparative Example 5, it can be seen that when the calcination atmosphere in step 2 is argon atmosphere, the initial 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 includes the following steps: S1. G-C3N4 nanosheets, lithium salt and NH4HCO3 are mixed in a solvent and then separated by solid-liquid separation to obtain g-C3N4-LiOH precursor; S2. The g-C3N4-LiOH precursor is calcined to obtain the positive electrode lithium replenishing agent; The preparation method of the g-C3N4 nanosheets includes the following steps: Urea was added to a covered crucible, and after the first calcination and cooling, the lid of the crucible was removed and a second calcination was performed to obtain the g-C3N4 nanosheets. The atmosphere for the first calcination was air, and the atmosphere for the second calcination was air. In step S2, the calcination atmosphere includes either an oxygen atmosphere or an air atmosphere, the calcination heating rate is 5~10℃ / min, and the calcination temperature is 300~400℃.

2. The method for preparing the positive electrode lithium supplement according to claim 1, characterized in that, In the preparation process of the g-C3N4 nanosheets, the heating rate of the first calcination is 5~10℃ / min, the temperature of the first calcination is 550~650℃, the heating rate of the second calcination is 1~10℃ / min, and the temperature of the second calcination is 500~600℃.

3. The method for preparing the positive electrode lithium replenishing agent 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 NH4HCO3 is (0.3~1.5):3; And / or, in step S1, the solvent includes anhydrous ethanol; And / or, in step S1, the mixing time is 6~10h; And / or, 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 40~60℃.

4. A positive electrode lithium replenishing agent, characterized in that, The positive electrode lithium replenishing agent is prepared by the preparation method according to any one of claims 1-3, and the positive electrode lithium replenishing agent includes g-C3N4 and lithium loaded on the g-C3N4.

5. The positive electrode lithium replenishing agent according to claim 4, characterized in that, The mass ratio of the g-C3N4 to the amount of lithium loaded on the g-C3N4 is 900: (0.3~1.5) mg / mmol.

6. A positive electrode sheet, characterized in that, The positive electrode sheet includes an active material and a positive electrode lithium replenishing agent; wherein the positive electrode lithium replenishing agent includes the positive electrode lithium replenishing agent according to claim 4 or 5 or the positive electrode lithium replenishing agent prepared by any one of claims 1-3.

7. The positive electrode sheet according to claim 6, characterized in that, The positive electrode sheet further 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).

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 6 or 7.

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