Efficient lithium carbonate composite positive electrode lithium supplement agent and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an efficient lithium carbonate composite positive electrode lithium supplement agent and a preparation method and application thereof. The composite positive electrode lithium supplementing agent provided by the invention comprises an M-N-C catalyst and lithium carbonate distributed in the M-N-C catalyst, and is prepared by dropping a lithium carbonate supersaturated aqueous solution into an organic solvent containing the M-N-C catalyst through an anti-solvent crystallization method. The composite positive electrode lithium supplementing agent is uniform in particle size distribution, transition metal in the composite positive electrode lithium supplementing agent is embedded into a carbon net of an N-C material through chemical action to form a two-dimensional or three-dimensional conductive network, and a high-activity place is provided for adsorption, desorption and decomposition of lithium carbonate. When being used as a lithium supplement additive in a lithium ion battery, the lithium ion battery electrolyte can greatly shorten the migration path of Li < + > in lithium carbonate and obviously reduce the decomposition potential of lithium carbonate, thereby providing higher charging capacity. In addition, the method provided by the invention has low requirements on production, processing and use environments, and can realize large-scale commercial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a high-efficiency lithium carbonate composite positive electrode lithium replenisher, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries, with their advantages of high energy density and long cycle life, are widely used in portable electronic devices, electric vehicles, and other fields. However, during the initial charge process, a solid electrolyte interface (SEI) forms on the surface of the anode. This process consumes active lithium, leading to a loss of positive electrode material capacity and significantly limiting battery performance. Positive electrode pre-lithiation technology, an effective means of addressing this problem, adds a lithium supplement to the cathode to provide additional active lithium for the formation of the SEI film, compensating for this loss and significantly improving the battery's capacity and cycle performance. Currently, commonly used lithium supplements, such as inorganic materials like Li2NiO2 and Li5FeO4, possess high theoretical capacities but suffer from significant drawbacks in practical applications. They are extremely sensitive to ambient humidity and require complex synthesis processes, increasing production costs and technical difficulties. Furthermore, residual metal oxides from these supplements reduce the battery's energy density, hindering further improvements in lithium-ion battery performance.

[0003] Organic lithium compounds, with their advantages such as good air stability and no residue after decomposition, have attracted much attention in the field of lithium replenishment for lithium-ion batteries. Lithium carbonate is a typical example. However, the application of lithium carbonate faces many difficulties. Its decomposition potential is above 4.75V, far exceeding the decomposition voltage of the electrolyte. This not only makes it difficult to decompose large amounts of lithium carbonate, deteriorating battery performance, but also reduces overall efficiency due to its poor conductivity. To address the problem of low lithium carbonate decomposition rate, reducing its particle size is an effective way to reduce the decomposition potential. However, the current method of reducing particle size is mainly high-temperature ball milling, which is costly. In addition, in the subsequent lithium replenishment process, oxygen evolution will also be faced, posing new challenges to battery safety and stability. Therefore, it is necessary to develop a high-efficiency composite positive electrode lithium replenisher containing lithium carbonate with low decomposition potential, high conductivity, and no oxygen evolution. Summary of the Invention

[0004] To overcome the shortcomings of the above-mentioned prior art, the present invention provides a high-efficiency lithium carbonate composite cathode lithium replenisher, which is an MNC catalyst / lithium carbonate composite cathode lithium replenisher (where M is one of the transition metals Fe, Co, Ni, Mn, Cu, Cr, V, Ti, Mo, Nb, W, etc.). The composite cathode lithium replenisher includes an MNC catalyst and lithium carbonate distributed within the MNC catalyst. By embedding the transition metal into a nitrogen-doped carbon (NC) material to form a highly active catalyst, the catalyst is composited with lithium carbonate to form a three-dimensional conductive network, significantly reducing the decomposition potential of the lithium carbonate and improving the charge capacity.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a high-efficiency lithium carbonate composite positive electrode lithium replenisher, the composite positive electrode lithium replenisher includes an MNC catalyst and lithium carbonate distributed inside the MNC catalyst, the mass proportion of the lithium carbonate in the composite positive electrode lithium replenisher is 0.1% to 95%, and the M is a transition metal including Fe, Co, Ni, Mn, Cu, Cr, V, Ti, Mo, Nb, and W;

[0007] The MNC catalyst is first prepared by using a carbon source and a nitrogen source to make an NC material, and then prepared by combining the NC material with a transition metal compound; the methods for preparing the NC material include electrocatalysis, MOF derivatization, hard template method, molecular catalyst template method, thermal decomposition, organic synthesis or solid phase synthesis; the methods for preparing the MNC catalyst by combining the NC material with a transition metal compound include high-temperature thermal decomposition, impregnation, electrochemical deposition / reduction, sequential etching / doping strategy, solid phase reduction or plasma enhanced chemical vapor deposition (PECVD).

[0008] In the present invention, the MNC catalyst has a porous structure, and the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher includes an MNC catalyst and lithium carbonate distributed inside the MNC catalyst. The lithium carbonate is distributed inside the MNC catalyst, which means that the lithium carbonate is distributed in the pores of the MNC catalyst. This not only improves the conductivity of the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher, but also solves the problem of small lithium carbonate particles agglomerating when the composite positive electrode lithium replenisher is homogenized in the positive electrode slurry.

[0009] In the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher of the present invention, the mass proportion of lithium carbonate can be 35%, 40%, 45%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc., as long as the mass proportion of lithium carbonate is within the range of 0.1% to 95%. Preferably, the mass proportion of lithium carbonate in the composite positive electrode lithium replenisher is 85% to 95%. Within this preferred range, the mass proportion of lithium carbonate is high, and the lithium content is high, which can replenish the active lithium lost in the formation of the SEI film and improve the specific capacity of the battery positive electrode material. Moreover, at this time, the mass proportion of the MNC catalyst is within the range of 5% to 15%, which has the effect of improving the conductivity of the lithium replenisher.

[0010] In the MNC catalyst / lithium carbonate composite positive electrode replenisher, the mass proportion of lithium carbonate is within the range of 85% to 95%, which can ensure that the replenisher has sufficient lithium to replenish the active lithium consumed in the formation of the SEI film, thereby improving the specific capacity of the battery positive electrode material. If the mass content of lithium carbonate is less than 80%, to replenish the active lithium lost in the formation of the SEI film, a larger amount of lithium replenisher must be added, the amount of inactive material increases, and the battery energy density decreases. If the mass content of lithium carbonate is higher than 95%, the MNC catalyst content is low, the conductivity of the replenisher is reduced, and the decomposition rate of the replenisher is reduced.

[0011] Preferably, the average pore size of the MNC catalyst is 0.1 to 140 nm, and the average particle size of the lithium carbonate is in the range of 0.1 to 30 nm;

[0012] The average particle size of lithium carbonate is in the range of 0.1 to 30 nm, which can reduce the decomposition potential of lithium carbonate. The composite positive electrode lithium supplement provided by the present invention has a decomposition potential of lithium carbonate reduced to 4.3 V, reducing the damage to the electrolyte caused by traditional high-voltage decomposition and ensuring the long-term cycle stability of the battery.

[0013] More preferably, the particle size of lithium carbonate is less than or equal to the pore size of the MNC catalyst, so that the lithium carbonate can be distributed inside the MNC catalyst.

[0014] More preferably, the average pore size of the MNC catalyst is 1 to 10 nm. Small pore size MNC catalysts can further reduce the particle size of lithium carbonate distributed inside, significantly improve its electrochemical activity, and further reduce the decomposition potential of lithium carbonate.

[0015] Preferably, the preparation method of the MNC catalyst comprises the following steps:

[0016] S1, heating the carbon source and the nitrogen source to 500-800° C. in an air atmosphere and calcining for 0.5-24 hours to obtain the NC material;

[0017] S2, mixing the NC material with NaH2PO2·H2O, heating the mixture to 200-400°C in an inert gas atmosphere and maintaining the temperature for 1-3 hours to form a phosphorus-doped NC material;

[0018] S3, after dispersing the phosphorus-doped NC material in water, adding an aqueous solution containing a transition metal compound, and then stirring the reaction in an oil bath at 60-80° C. for 3-7 hours;

[0019] S4. After drying the above mixture, heating it at 250-350° C. under an inert gas atmosphere for 1-3 hours, and then washing and drying it to obtain an MNC catalyst.

[0020] More preferably, the carbon source includes urea, polyaniline (PANI), polypyrrole, polydopamine, ZIF-8 (zinc-based MOF), sucrose, glucose, chitosan, carbon nanotubes (CNTs), and graphene oxide (GO); the nitrogen source includes polyaniline (PANI), polypyrrole, polydopamine, melamine, urea, formamide ZIF-8 (zinc-based MOF), gelatin, sucrose, glucose, chitosan, ionic liquids (such as [BMIM][BF4]), ammonia (NH3), cyanamide compounds (such as dicyandiamide), and amino acids; the transition metal-containing compound is one of transition metal oxides, transition metal carbides, transition metal nitrides, transition metal phosphides, and transition metal sulfides.

[0021] More preferably, the calcination temperature in S1 is 500° C. to 800° C., and the calcination time is 1 h to 10 h.

[0022] The second aspect of the present invention provides a method for preparing the high-efficiency lithium carbonate composite cathode lithium replenisher described in the first aspect, specifically: using an anti-solvent crystallization method, a supersaturated aqueous solution of lithium carbonate is dropped into an organic solvent containing an MNC catalyst, stirred, and then vacuum dried to evaporate the solvent. The lithium carbonate particles are deposited inside the MNC catalyst, thereby forming an MNC catalyst / lithium carbonate composite cathode lithium replenisher.

[0023] The present invention provides a method for preparing a composite positive electrode lithium supplement. The method involves uniformly mixing an MNC catalyst with carbonic acid using a solvent-dissolving crystallization method. The resulting lithium carbonate is then placed within the MNC catalyst, further reducing the particle size of the lithium carbonate, significantly improving its electrochemical activity and lowering its decomposition potential. The porous carbon also exhibits high electrical conductivity, which improves the conductivity of the composite positive electrode lithium supplement. The present invention provides a simple, easy-to-use, low-energy-consumption method that is readily available for large-scale production.

[0024] Preferably, the holding temperature is 50°C to 300°C for 1 to 10 hours. More preferably, the holding temperature is in the range of 50°C to 110°C. At this temperature, the lithium carbonate content distributed in the pores of the MNC catalyst is high, and the lithium carbonate activity in the porous carbon pores is high. Therefore, within this temperature range, the decomposition rate of lithium carbonate is high.

[0025] Preferably, the mass ratio of the MNC catalyst to lithium carbonate is (0.0526-999): 1. More preferably, the mass ratio of the MNC catalyst to carbonic acid is 1: (9-16).

[0026] The mass ratio of the MNC catalyst to the carbonic acid is within the above range, which facilitates the preparation of the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher with a lithium carbonate mass ratio within the range of 0.1% to 95%. If the mass ratio is too high, the lithium carbonate content in the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher is low, the lithium carbonate mass ratio per unit mass of the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher decreases, and the decomposed active lithium in the resulting composite positive electrode lithium replenisher decreases. If the mass ratio is too low, the lithium carbonate content per unit mass of the MNC catalyst / lithium carbonate composite positive electrode lithium replenisher is high, and the lithium carbonate mass ratio of the resulting MNC catalyst / lithium carbonate composite positive electrode lithium replenisher exceeds 95%, the MNC catalyst content decreases, and the conductivity of the composite positive electrode lithium replenisher decreases.

[0027] Preferably, the organic solvent is a solvent with low solubility for lithium carbonate, preferably ethanol.

[0028] A third aspect of the present invention provides a positive electrode, which includes the high-efficiency lithium carbonate composite positive electrode lithium replenisher described in the first aspect.

[0029] Preferably, the preparation method of the positive electrode is: mixing the positive electrode active material, the binder, the conductive agent and the high-efficiency lithium carbonate composite positive electrode lithium supplement according to any one of claims 1 to 5, dissolving them in a solvent to prepare a positive electrode slurry, and then coating to obtain a positive electrode sheet, wherein the coated single-side surface density is 200 to 400 g / m 2 .

[0030] Lithium carbonate is distributed within the MNC catalyst, making it difficult to agglomerate during the preparation of the positive electrode slurry, without changing the original slurry properties or affecting the normal coating of the slurry, allowing for large-scale production of positive electrodes. It should be noted that the positive electrode provided herein comprises a positive electrode active material, a conductive agent, and a binder, and that the positive electrode active material, conductive agent, and binder are all prior art. More preferably, the positive electrode active material comprises NCM811, NCM622, or NCM523, the binder comprises polyvinylidene fluoride (PVDF), and the conductive agent comprises conductive carbon black, carbon nanotubes, or graphene.

[0031] A fourth aspect of the present invention provides a lithium-ion battery, comprising the positive electrode described in the third aspect.

[0032] By using the composite positive electrode lithium replenisher of the present invention, the decomposition potential of the lithium carbonate in the composite positive electrode lithium replenisher is reduced to 4.3V. During the charge and discharge process of the battery, the lithium carbonate decomposes into active lithium, which replenishes the active lithium consumed by the formation of the SEI film, thereby improving the gram capacity of the battery positive electrode material. The MNC catalyst in the composite positive electrode lithium replenisher can improve the conductivity of the composite positive electrode lithium replenisher and enhance the decomposition rate of the composite positive electrode lithium replenisher.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention discloses a high-efficiency lithium carbonate composite positive electrode lithium replenishing material, and its preparation method comprises the following steps: dripping a supersaturated aqueous solution of lithium carbonate into an organic solvent containing an MNC catalyst, and subjecting the lithium carbonate to a dissolution-recrystallization cycle through an anti-solvent crystallization method, thereby reducing the particle size of the lithium carbonate and simultaneously precipitating it in situ on the catalyst, and finally drying the lithium carbonate composite positive electrode lithium replenishing agent. The MNC catalyst is an NC material embedded with a transition metal. The lithium carbonate composite positive electrode lithium replenishing agent prepared by the present invention has a uniform particle size distribution, and the transition metal in the catalyst is chemically embedded in the carbon network of the NC material to form a two-dimensional or three-dimensional conductive network, which has a rich conductive network and provides a highly active site for the adsorption, desorption and decomposition of lithium carbonate. When it is used as a lithium replenishing additive in lithium-ion batteries, the Li + The migration path significantly reduces the decomposition potential of lithium carbonate, thereby providing a higher charge capacity. In addition, the method of the present invention has low requirements for production, processing and use environment, and can be used in large-scale commercial applications.

[0035] Specifically, the present invention has the following advantages:

[0036] (1) Lithium carbonate is distributed inside the MNC catalyst, which reduces the particle size of lithium carbonate and significantly improves its electrochemical activity, reduces the decomposition potential of lithium carbonate (the decomposition potential of lithium carbonate can be reduced to 4.3V), and increases the decomposition rate of lithium carbonate; during the battery charge and discharge process, the lithium carbonate in the composite positive electrode lithium replenisher can decompose and effectively play a lithium replenishing role. (2) The catalyst containing MNC can improve the conductivity of the composite positive electrode lithium replenisher and increase the decomposition rate of the composite positive electrode lithium replenisher. (3) When the composite positive electrode lithium replenisher is used as a lithium replenishing additive for positive electrode slurry homogenization, the MNC catalyst is located outside the lithium carbonate, which can effectively prevent lithium carbonate from agglomerating, does not affect the normal homogenization of the positive electrode slurry, ensures the normal slurry coating, and can be used for large-scale preparation of lithium-ion batteries. (4) The MNC catalyst can absorb the oxygen generated by the decomposition of lithium carbonate, reducing the adverse effects of oxygen on the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the SEM image of Ru-NC catalyst;

[0038] Figure 2 is the pore size image of Ru-NC catalyst;

[0039] Figure 3 This is an image of the particle size of lithium carbonate prepared by the anti-solvent method;

[0040] Figure 4This is the SEM image of the Ru-NC catalyst / lithium carbonate high-efficiency composite cathode lithium replenisher;

[0041] Figure 5 XRD images of Ru-NC catalyst / lithium carbonate high-efficiency composite cathode lithium replenisher, commercial lithium carbonate and Ru-NC catalyst;

[0042] Figure 6 This is the charging curve image of the Ru-NC catalyst / lithium carbonate high-efficiency composite positive electrode lithium replenisher. DETAILED DESCRIPTION

[0043] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0044] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0045] Example 1

[0046] This embodiment provides a high-efficiency composite positive electrode lithium supplement and a corresponding lithium-ion battery, comprising the following steps:

[0047] 1. Preparation of composite positive electrode lithium supplement:

[0048] (1) 10 g of urea was heated at 5°C·min -1 The mixture was heated to 600 °C at a heating rate of 1000 ℃ and kept in air atmosphere for 2 hours, and then naturally cooled to room temperature to obtain yellow powdery g-C3N4 nanosheets.

[0049] (2) 300 mg of the obtained g-C3N4 nanosheets were fully mixed with 1.5 g of NaH2PO2·H2O and ground for 30 min; then -1 The mixture was heated to 300 °C at a heating rate of 1000 ℃ and maintained in an argon atmosphere for 2 h to obtain PCN powder.

[0050] (3) 200 mg PCN was dispersed in a flask containing 60 mL deionized water and continuously ultrasonicated for 30 min. Then 1.0 mL RuCl3 aqueous solution (10 mg mL -1 ) was dropped into a uniform PCN aqueous solution and stirred in an oil bath at 70 °C for 5 h.

[0051] (4) The mixture was further dried by rotary evaporation and then transferred to a tube furnace and heated at 300°C for 2 hours under an argon atmosphere. The obtained powder was ultrasonically mixed, washed several times with deionized water, and finally dried in vacuum at 60°C overnight to obtain the Ru-NC catalyst.

[0052] (5) adding 100 g of lithium carbonate powder to pure water to prepare a supersaturated aqueous solution of lithium carbonate with a solid content of 20%, and stirring and dispersing the solution to obtain a first slurry;

[0053] (6) adding 5 g of the Ru-NC catalyst obtained in step (4) to 500 mL of anhydrous ethanol solvent to prepare a catalyst slurry with a solid content of 1%, and performing ultrasonic dispersion to obtain a second slurry material;

[0054] (7) The first slurry was dripped into the second slurry at 0°C at a rate of 1 drop / second, and the slurry was stirred at a speed of 800 rpm / min for 10 minutes. After vacuum drying at 80°C for 10 hours, a Ru-NC catalyst / lithium carbonate composite positive electrode lithium supplement was obtained.

[0055] 2. Preparation of positive electrode sheet:

[0056] NCM811, the composite positive electrode lithium supplement agent prepared above, PVDF (polyvinylidene fluoride), and conductive carbon black were mixed in a mass ratio of 100:2.5:3:2, and solvent NMP (N-methylpyrrolidone) was added to keep the solid content at 45%. After stirring evenly, a positive electrode slurry was prepared, and then the positive electrode slurry was coated to obtain a positive electrode sheet. The coated single-side surface density was 300g / m 2 , followed by roller pressing and tableting processes.

[0057] 3. Preparation of lithium-ion batteries:

[0058] The prepared positive electrode sheet, lithium sheet, and PP separator were stacked and assembled in a button-type battery case in a glove box. An appropriate amount of electrolyte was then injected and sealed to form a button-type half-cell. The battery was then aged and formed in this manner.

[0059] The aging process is as follows: place the half-cell in a 30°C oven for 12 hours.

[0060] The formation process is as follows: first, the half-cell is charged at a current of 0.05C for 2 hours, followed by a constant current and constant voltage charge at 0.2C until the voltage reaches 3.8V. Charging is stopped when the current drops to 0.05C. Next, the battery is switched to a constant current and constant voltage charge at 0.03C, raising the voltage to 4.3V (the decomposition voltage of lithium carbonate in the composite positive electrode lithium supplement prepared above). This charging phase ends when the current drops to 0.005C. After that, the battery is discharged at a current of 0.5C to 2V, and finally a constant current and constant voltage charge at 0.5C is performed to 3.8V, with a cut-off current of 0.05C.

[0061] Example 2

[0062] The difference between Example 2 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with the FeCl3 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Fe-NC catalyst / lithium carbonate.

[0063] Example 3

[0064] The difference between Example 3 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a CoCl2 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Co-NC catalyst / lithium carbonate.

[0065] Example 4

[0066] The difference between Example 4 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a NiCl2 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Ni-NC catalyst / lithium carbonate.

[0067] Example 5

[0068] The difference between Example 5 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a MnCl2 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Mn-NC catalyst / lithium carbonate.

[0069] Example 6

[0070] The difference between Example 6 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a CuCl2 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Cu-NC catalyst / lithium carbonate.

[0071] Example 7

[0072] The difference between Example 7 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a CrCl2 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Cr-NC catalyst / lithium carbonate.

[0073] Example 8

[0074] The difference between Example 8 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a VCl3 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is VNC catalyst / lithium carbonate.

[0075] Example 9

[0076] The difference between Example 9 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a TiCl3 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Ti-NC catalyst / lithium carbonate.

[0077] Example 10

[0078] The difference between Example 10 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a MoCl5 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Mo-NC catalyst / lithium carbonate.

[0079] Example 11

[0080] The difference between Example 11 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with the NbCl5 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is Nb-NC catalyst / lithium carbonate.

[0081] Example 12

[0082] The difference between Example 12 and Example 1 is that when preparing the composite positive electrode lithium replenisher, the RuCl3 aqueous solution in step (3) is replaced with a WCl6 aqueous solution, and the rest is the same as Example 1. Finally, the composite positive electrode lithium replenisher obtained is WNC catalyst / lithium carbonate.

[0083] Example 13

[0084] The composite positive electrode lithium supplement in this embodiment is lithium carbonate prepared by the anti-solvent crystallization method (Note: the lithium carbonate used in Examples 1-12 is also prepared by the anti-solvent crystallization method). The preparation method includes the following steps:

[0085] (1) adding 100 g of lithium carbonate powder to pure water to prepare a supersaturated aqueous solution of lithium carbonate with a solid content of 20%, and stirring and dispersing the solution to obtain a first slurry;

[0086] (2) The first slurry was dripped into 500 mL of anhydrous ethanol solvent at 0°C at a rate of 1 drop / second, and the slurry was stirred at 800 rpm / min for 10 min, centrifuged at 8000 rpm / min for 10 min, and vacuum dried at 60°C to obtain recrystallized lithium carbonate.

[0087] Comparative Example 1

[0088] This comparative example provides a conventional lithium-ion battery, which is different from Example 1 in that no composite positive electrode lithium replenisher is used in Comparative Example 1.

[0089] Comparative Example 2

[0090] This comparative example provides a lithium-ion battery using a conventional lithium supplement. Compared with Example 1, the difference is that commercial lithium carbonate is used in Comparative Example 2.

[0091] Comparative Example 3

[0092] This comparative example provides a Ru-NC lithium supplement and a corresponding lithium ion battery. Compared with Example 1, the difference is that: in Comparative Example 3, Ru-NC catalyst is used as the lithium supplement.

[0093] Comparative Example 4

[0094] The comparative example provides a composite lithium supplement and a corresponding lithium ion battery. Compared with Example 1, the difference is that the composite lithium supplement used in Comparative Example 4 is prepared by simply mixing Ru-NC catalyst and commercial lithium carbonate (the catalyst accounts for 10 wt% of lithium carbonate).

[0095] Experimental Example 1: Characterization of MNC catalyst / lithium carbonate composite cathode lithium supplement

[0096] like Figure 1 As shown in FIG, the prepared Ru-NC catalyst is a three-dimensional conductive network composed of a carbon-nitrogen material matrix NC and a transition metal Ru embedded in the matrix. Figure 2 As shown in Figure 2, the pore size of the Ru-NC catalyst obtained is mainly distributed between 2-4.5 nm, and a few are between 10-13 nm, while the average particle size of lithium carbonate prepared by the anti-solvent crystallization method is between 0.1-10 nm ( Figure 3 ).

[0097] Transition metals are chemically embedded in the carbon network of NC materials, and saturated lithium carbonate solution is dripped into the catalyst solution through the anti-solvent crystallization method to make lithium carbonate undergo dissolution-recrystallization cycle. While the particle size of lithium carbonate is reduced, it can be well adsorbed on the three-dimensional conductive network of the catalyst, thereby forming a Figure 4 MNC catalyst / lithium carbonate composite material shown.

[0098] like Figure 5 As shown in the XRD image, compared with commercial lithium carbonate, the prepared Ru-NC catalyst / lithium carbonate composite cathode lithium replenisher has additional peaks belonging to the Ru-NC catalyst at 36° and 43°, indicating that the Ru-NC catalyst is successfully composited with lithium carbonate.

[0099] In addition, the SEM, pore size and XRD test results of Examples 2-12 are substantially the same as those of the Ru-NC catalyst / lithium carbonate composite material of Example 1.

[0100] Experimental Example 2: Performance test of lithium-ion battery based on MNC catalyst / lithium carbonate composite cathode lithium supplement

[0101] (1) Performance test:

[0102] The lithium ion batteries prepared in Examples 1-13 and Comparative Examples 1-4 were charged and discharged, and the initial charge voltage platform and initial charge specific capacity were recorded. The decomposition rate of lithium carbonate was also calculated. The specific data are recorded in Table 1. The method for calculating the decomposition rate of lithium carbonate in the composite positive electrode lithium supplement is as follows:

[0103] Decomposition rate of composite positive electrode lithium supplement = (C1-C4) / a×w1×w2×b;

[0104] Wherein, C1 is the discharge capacity of the battery obtained after adding the composite positive electrode lithium replenisher prepared above; C4 is the discharge capacity obtained without adding the composite positive electrode lithium replenisher; a is the amount of the composite positive electrode lithium replenisher added in the preparation of the positive electrode sheet; b is the gram capacity of lithium carbonate; w1 is the mass ratio of lithium carbonate in each gram of MNC catalyst / lithium carbonate composite positive electrode lithium replenisher; w2 is the mass ratio of MNC catalyst / lithium carbonate and NCM811 per gram;

[0105] NCM811 gram capacity = C1 / m2, where m2 is the mass of NCM in the preparation of the positive electrode sheet.

[0106] In Examples 1-12, w1 is 95%, w2 is 5%, and b is 725 mAh / g.

[0107] (2) Experimental results:

[0108] As shown in Table 1, in Examples 1-13, due to the use of MNC catalyst / lithium carbonate composite positive electrode lithium supplement, the lithium carbonate decomposition rate is above 60%, and can even be as high as 99%. The higher lithium carbonate decomposition rate indicates that the internal active substances of the battery can be better activated in the initial state, which is beneficial to the subsequent battery performance, allowing the battery to store more electricity during the first charge, and having more advantages in battery capacity performance, which is beneficial to improving the battery life. Figure 6 As shown, the charge specific capacity of Example 1 is 265.2 mAh / g, the charge voltage platform is less than 3.90 V, and the voltage platform is obvious; while the charge specific capacity of Comparative Example 1 is only 215.0 mAh / g, and the constant voltage charge is significantly higher, and the charge voltage platform is high and not obvious, indicating that lithium carbonate is adsorbed on the three-dimensional conductive network of the MNC catalyst through the anti-solvent method. Not only does the lithium carbonate have a reduced particle size, but also, under the catalysis of the MNC catalyst, the decomposition voltage of lithium carbonate can be significantly reduced, the decomposition efficiency can be improved, and the charge capacity can be increased at the same time.

[0109] In contrast, the positive electrode sheet in Comparative Example 2 uses commercial lithium carbonate as a positive electrode lithium replenisher. Although there is a certain improvement in specific capacity compared to Comparative Example 1, the decomposition rate of lithium carbonate is only 10%, and the decomposition voltage is relatively high. At the same time, according to Comparative Example 3, Comparative Example 3 uses the Ru-NC catalyst in the MNC catalyst of the present invention as an additive, which has no significant effect on the initial charge specific capacity of the battery, indicating that the catalytic effect of MNC can significantly reduce the decomposition voltage of lithium carbonate and improve the decomposition efficiency. In addition, as can be seen from Comparative Example 4, Comparative Example 4 simply mixes the Ru-NC catalyst in the MNC catalyst with commercial lithium carbonate as a composite positive electrode lithium replenisher. Compared with Examples 1-13, under this composite method, the catalytic effect of the Ru-NC catalyst cannot be well exerted, the decomposition rate of lithium carbonate is only slightly improved, and the decomposition voltage does not decrease. This shows that the simple mixing of the MNC catalyst and lithium carbonate has limited effect on reducing the decomposition voltage of lithium carbonate and improving the decomposition rate.

[0110] Table 1 Battery data of each embodiment and comparative example

[0111]

[0112] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A high-efficiency lithium carbonate composite positive electrode lithium supplement, characterized in that: The composite positive electrode lithium replenisher includes an MNC catalyst and lithium carbonate distributed inside the MNC catalyst, wherein the mass proportion of the lithium carbonate in the composite positive electrode lithium replenisher is 0.1% to 95%, and M is a transition metal including Fe, Co, Ni, Mn, Cu, Cr, V, Ti, Mo, Nb, and W; The MNC catalyst is first prepared by using a carbon source and a nitrogen source to make an NC material, and then prepared by combining the NC material with a transition metal compound; the methods for preparing the NC material include electrocatalysis, MOF derivatization, hard template method, molecular catalyst template method, thermal decomposition, organic synthesis or solid phase synthesis; the methods for preparing the MNC catalyst by combining the NC material with a transition metal compound include high-temperature thermal decomposition, impregnation, electrochemical deposition / reduction, sequential etching / doping strategy, solid phase reduction or plasma-enhanced chemical vapor deposition.

2. The high-efficiency lithium carbonate composite positive electrode lithium supplement according to claim 1, characterized in that: The mass proportion of the lithium carbonate in the composite positive electrode lithium replenisher is 85% to 95%.

3. The high-efficiency lithium carbonate composite positive electrode lithium supplement according to claim 1, characterized in that: The average pore size of the MNC catalyst is 0.1-140 nm, and the average particle size of the lithium carbonate is in the range of 0.1-30 nm.

4. The high-efficiency lithium carbonate composite positive electrode lithium supplement according to claim 1, characterized in that: The preparation method of the MNC catalyst comprises the following steps: S1, heating the carbon source and the nitrogen source to 500-800° C. in an air atmosphere and calcining for 0.5-24 hours to obtain the NC material; S2, mixing the NC material with NaH2PO2·H2O, heating the mixture to 200-400°C in an inert gas atmosphere and maintaining the temperature for 1-3 hours to form a phosphorus-doped NC material; S3, after dispersing the phosphorus-doped NC material in water, adding an aqueous solution containing a transition metal compound, and then stirring the reaction in an oil bath at 60-80° C. for 3-7 hours; S4. After drying the above mixture, heating it at 250-350° C. under an inert gas atmosphere for 1-3 hours, and then washing and drying it to obtain an MNC catalyst.

5. The high-efficiency lithium carbonate composite positive electrode lithium supplement according to claim 4, characterized in that: The carbon source includes urea, polyaniline, polypyrrole, polydopamine, ZIF-8, sucrose, glucose, chitosan, carbon nanotubes, and graphene oxide; the nitrogen source includes polyaniline, polypyrrole, polydopamine, melamine, urea, formamide ZIF-8, gelatin, sucrose, glucose, chitosan, ionic liquid, ammonia, cyanamide compounds, and amino acids; and the transition metal compound is one of transition metal oxides, transition metal carbides, transition metal nitrides, transition metal phosphides, and transition metal sulfides.

6. The method for preparing the high-efficiency lithium carbonate composite positive electrode lithium supplement according to any one of claims 1 to 5, characterized in that: Through the anti-solvent crystallization method, a supersaturated aqueous solution of lithium carbonate is dropped into an organic solvent containing an MNC catalyst, stirred, and then vacuum dried to evaporate the solvent. The lithium carbonate particles are deposited inside the MNC catalyst, thereby forming an MNC catalyst / lithium carbonate composite positive electrode lithium replenisher.

7. The method for preparing a high-efficiency lithium carbonate composite positive electrode lithium supplement according to claim 6, characterized in that: The temperature of the heat preservation treatment is 50℃~300℃, and the time is 1h~10h.

8. A positive electrode, characterized in that The positive electrode comprises the high-efficiency lithium carbonate composite positive electrode lithium replenisher according to any one of claims 1 to 5.

9. A positive electrode according to claim 8, characterized in that: The preparation method of the positive electrode comprises: mixing a positive electrode active material, a binder, a conductive agent and the high-efficiency lithium carbonate composite positive electrode lithium supplement agent according to any one of claims 1 to 5, dissolving the mixture in a solvent to prepare a positive electrode slurry, and then coating the mixture to prepare a positive electrode sheet, wherein the coated single-side surface density is 200 to 400 g / m 2 .

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

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