Modified lithium carbonate positive electrode lithium supplement and application thereof

Abstract

The application discloses a modified lithium carbonate positive electrode lithium supplement and application thereof, and the component of the lithium carbonate positive electrode lithium supplement is a Li2CO3 / transition metal oxide heterojunction composite material, wherein the transition metal includes one or more of Co, Fe, Ni and Mn. Specifically, after lithium carbonate is dissolved, a transition metal salt source is added, and a Li2CO3 / transition metal oxide heterojunction is generated through anti-solvent precipitation and heat treatment. The positive electrode lithium supplement significantly reduces the decomposition potential of Li2CO3, and when applied to a positive electrode material, the decomposition potential can be further reduced, and is highly matched with an existing positive electrode working window. The decomposition efficiency of the positive electrode lithium supplement is high, and the irreversible lithium loss in the first charge-discharge process of a lithium ion battery can be effectively compensated. The positive electrode and the lithium ion battery containing the positive electrode lithium supplement have higher first coulomb efficiency, energy density and excellent cycle stability. The application realizes efficient decomposition of Li2CO3 under extremely low catalyst consumption, solves the problem of too high proportion of non-active components, and has extremely high industrial application value.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular, to a modified lithium carbonate cathode lithium replenisher and its application. Background Technology

[0002] During the first charge of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This irreversibly consumes a significant amount of active lithium from the positive electrode, leading to a decrease in the battery's initial coulombic efficiency and initial energy density. To compensate for this loss of active lithium, pre-lithiation technology has emerged. Among these technologies, positive electrode lithium replenishment technology has attracted considerable attention due to its advantages such as good compatibility with existing battery manufacturing processes, simple operation, and high safety.

[0003] Lithium carbonate (Li₂CO₃) has a theoretically high specific capacity (724 mAh g⁻¹). -1 Li₂CO₃ possesses advantages such as excellent air stability, low cost, and gaseous decomposition products with no solid residue, making it an ideal cathode material for lithium replenishment. However, Li₂CO₃ has extremely poor intrinsic electronic conductivity and slow decomposition kinetics, resulting in a decomposition potential in practical applications that is much higher than its theoretical value (>4.75V), and far higher than the upper limit of the operating voltage of most commercial cathode materials (typically ≤4.3V). This makes it difficult for it to effectively decompose and release active lithium in conventional battery systems.

[0004] In existing technologies, researchers have explored strategies such as particle refinement, compositing with highly conductive agents, and introducing catalysts to reduce the decomposition potential of Li₂CO₃. For example, while adding catalysts such as Mo₂C and NiO can reduce the decomposition potential to some extent, the amount of catalyst used is typically as high as 20-30 wt%. The introduction of these inactive components significantly reduces the effective lithium replenishment capacity of the lithium replenishing agent. Therefore, the key to promoting the practical application of Li₂CO₃-based lithium replenishing agents lies in minimizing the amount of inactive catalysts while ensuring efficient catalytic decomposition. Summary of the Invention

[0005] The purpose of this invention is to provide a modified lithium carbonate cathode lithium replenishing agent and its application. By constructing a Li2CO3 / transition metal oxide heterojunction, the decomposition potential of Li2CO3 is significantly reduced and its decomposition efficiency is improved with extremely low catalyst dosage, thereby effectively compensating for the first irreversible capacity loss of lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides a Li₂CO₃ / transition metal oxide heterojunction composite material, wherein the transition metal oxide is LiCoO₂, LiFeO₂, LiNiO₂, LiMnO₂, or Li(Co)₂. x Fe y Ni z Mnw O2, where x+y+z+w=1, and the mass of the transition metal oxide is 1 to 5% of the mass of Li2CO3.

[0007] Preferably, in the Li2CO3 / transition metal oxide heterojunction composite material, a heterojunction interface with close contact is formed between the transition metal oxide and Li2CO3.

[0008] Preferably, the mass of the transition metal oxide is 3% of the mass of Li2CO3.

[0009] This invention also provides a method for preparing the aforementioned Li2CO3 / transition metal oxide heterojunction composite material, comprising the following steps: S1. First, dissolve commercial lithium carbonate in deionized water to obtain a lithium carbonate solution; S2. Then add a transition metal salt source to the lithium carbonate solution obtained in step S1, stir and mix evenly to obtain a mixed solution; S3. Slowly add the mixed solution obtained in step S2 into the antisolvent to precipitate the precipitate. After filtration, washing and drying, the precursor powder is obtained. S4. The precursor powder obtained in step S3 is heat-treated in an air atmosphere to obtain the Li2CO3 / transition metal oxide heterojunction composite material.

[0010] Preferably, in step S1, the ratio of commercial lithium carbonate to deionized water is 1g:40-60mL, and more preferably 1g:50mL.

[0011] Preferably, in step S2, the transition metal salt source is one or more of soluble cobalt salt, iron salt, nickel salt, and manganese salt.

[0012] Preferably, the transition metal salt source is one or more of cobalt nitrate hexahydrate, ferric nitrate nonahydrate, nickel nitrate hexahydrate, and manganese nitrate tetrahydrate.

[0013] More preferably, the transition metal salt source is cobalt nitrate hexahydrate, and its amount is 0.0245 to 0.1215 times the mass of commercial lithium carbonate, more preferably 0.073 times; the transition metal salt source is ferric nitrate nonahydrate, and its amount is 0.0755 times the mass of commercial lithium carbonate; the transition metal salt source is nickel nitrate hexahydrate, and its amount is 0.074 times the mass of commercial lithium carbonate; the transition metal salt source is manganese nitrate tetrahydrate, and its amount is 0.0715 times the mass of commercial lithium carbonate; the transition metal salt source is a combination of ferric nitrate nonahydrate and nickel nitrate hexahydrate, and their amounts are 0.038 times and 0.037 times the mass of commercial lithium carbonate, respectively.

[0014] Preferably, in step S3, the antisolvent is anhydrous ethanol, which has the same volume as the deionized water used in step S1.

[0015] Preferably, in step S3, the precipitate is filtered, washed three times with anhydrous ethanol, and dried in a vacuum drying oven at 60°C for 12 hours to obtain the precursor powder.

[0016] Preferably, in step S4, the heat treatment conditions are: heating rate 2-10℃ / min, temperature 400-600℃, and time 2-8 hours.

[0017] Further preferred heat treatment conditions are: heating rate 5℃ / min, temperature 500℃, and time 5 hours.

[0018] This invention also provides the application of the aforementioned Li2CO3 / transition metal oxide heterojunction composite material as a positive electrode lithium replenisher.

[0019] The present invention also provides a modified lithium carbonate cathode lithium replenishing agent, the composition of which is the aforementioned Li2CO3 / transition metal oxide heterojunction composite material.

[0020] This invention also provides the application of the aforementioned modified lithium carbonate cathode lithium replenishing agent in the preparation of cathode plates.

[0021] The present invention also provides a positive electrode sheet, comprising a positive current collector and a positive active material layer coated on the positive current collector, wherein the positive active material layer contains the aforementioned modified lithium carbonate positive electrode lithium supplementer.

[0022] Preferably, the modified lithium carbonate cathode lithium replenishing agent accounts for 1 to 10% of the mass of the cathode active material layer.

[0023] The present invention also provides a lithium-ion battery, comprising the aforementioned positive electrode, negative electrode, separator, and electrolyte.

[0024] Preferably, the negative electrode is a Si / C@Gr(Graphite) negative electrode, the separator is a polypropylene separator (Celgard 2303), and the electrolyte is a 1 mol / L LiPF6 ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio 3:7) solution with 2 w.t.% vinylene carbonate (VC) added.

[0025] The present invention has the following beneficial effects: This invention discloses a modified lithium carbonate cathode lithium replenisher and its application. Its composition is a Li₂CO₃ / transition metal oxide heterojunction composite material. Specifically, after dissolving lithium carbonate, a cobalt source is added, and a Li₂CO₃ / transition metal oxide heterojunction is generated in situ through antisolvent precipitation and heat treatment. This cathode lithium replenisher significantly reduces the decomposition potential of Li₂CO₃ from above 4.75V to below 4.6V. When applied to cathode materials, its decomposition potential can be further reduced to approximately 4.0V, highly matching the operating window of existing cathodes. The decomposition efficiency of this cathode lithium replenisher is as high as 98% or more, effectively compensating for irreversible lithium loss during the first charge-discharge process of lithium-ion batteries. Cathodes and lithium-ion batteries containing this cathode lithium replenisher exhibit higher initial coulombic efficiency, energy density, and excellent cycle stability. This invention achieves highly efficient decomposition of Li₂CO₃ with extremely low catalyst dosage, solving the problem of excessively high proportion of inactive components, and has extremely high industrial application value.

[0026] The specific advantages of this invention are as follows: 1. Significantly reduced decomposition potential and high lithium replenishment efficiency: This invention significantly reduces the decomposition energy barrier of Li2CO3 by constructing a Li2CO3 / transition metal oxide heterojunction in situ and utilizing the charge redistribution and built-in electric field at the heterojunction interface. The decomposition efficiency of the Li2CO3 / transition metal oxide composite material can reach over 98.58% within a voltage window of 2.5-4.7V, which is far higher than that of unmodified Li2CO3.

[0027] 2. Extremely low catalyst dosage and high lithium replenishment capacity: The mass fraction of the transition metal oxide that plays a catalytic role in this invention is only 1-5 wt% (optimally 3 wt%), far lower than the 20-30 wt% catalyst dosage in existing technologies. This significantly reduces the proportion of inactive components in the lithium replenishment agent, thus preserving the high capacity advantage of Li2CO3.

[0028] 3. Synergistic effect with cathode materials and good working voltage window matching: After adding the Li2CO3 / transition metal oxide lithium replenisher prepared in this invention to the commercial NCM811 cathode, its decomposition potential can be further reduced to about 4.0V, which perfectly matches the working voltage window of existing cathode materials. Efficient lithium replenishment can be achieved without changing the charging cutoff voltage of the battery.

[0029] 4. Improved interface stability and extended battery cycle life: During decomposition, this lithium supplement helps form stable CEI and SEI layers rich in inorganic components such as LiF on the surfaces of the positive and negative electrodes, effectively inhibiting electrolyte decomposition and reducing interfacial impedance, thereby significantly improving the cycle stability and energy density of the full cell. In NCM811‖Si / C@Gr full cells, the initial energy density can be increased by more than 20%, and the capacity retention after 200 cycles is significantly better than the group without the supplement.

[0030] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The images show scanning electron microscope (SEM) images of Li2CO3 with different LiCoO2 contents (1 wt%, 3 wt%, and 5 wt%), where a is 1 wt%, b is 3 wt%, and c is 5 wt%.

[0032] Figure 2 The image shown is a high-resolution transmission electron microscope (HRTEM) image of the Li2CO3 / LiCoO2 heterojunction composite material prepared in Example 1 of this invention. The inset is a fast Fourier transform (FFT) image of the corresponding region.

[0033] Figure 3 The first charge-discharge curves of the Li2CO3 / LiCoO2 heterojunction composite materials prepared in Examples 1, 2 and 3 of this invention are shown.

[0034] Figure 4 This is a comparison of the first cyclic voltammetry curves of the NCM811 cathode with the lithium supplement agent from Example 1 and the NCM811 cathode without the lithium supplement agent in Application Example 1 of the present invention.

[0035] Figure 5 This is a comparison chart of the cycle performance of the NCM811‖Si / C@Gr full cell with lithium replenishment agent added in Example 1 and the full cell without lithium replenishment agent added, in Application Example 2 of the present invention. Detailed Implementation

[0036] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0037] Example 1 This embodiment provides a method for preparing a Li2CO3 / LiCoO2 heterojunction composite material (LiCoO2 content 3 wt%): 1. Dissolve 2g of commercial Li2CO3 in 100 mL of deionized water and stir until completely dissolved.

[0038] 2. Add 0.146 g Co(NO3)2·6H2O to the above solution and continue stirring for 1 hour to ensure uniform dispersion of the cobalt source.

[0039] 3. Under vigorous stirring, the mixed solution obtained in step 2 was slowly added dropwise to 100 mL of anhydrous ethanol, resulting in the precipitation of a white precipitate. The precipitate was filtered, washed three times with ethanol, and dried in a vacuum drying oven at 60°C for 12 hours to obtain the precursor powder.

[0040] 4. Place the precursor powder in a tube furnace and heat it to 500°C at a rate of 5°C / min under an air atmosphere. Hold the temperature for 5 hours and allow it to cool naturally to room temperature to obtain the final product, which is the Li2CO3 / LiCoO2 heterojunction composite material.

[0041] Example 2 This embodiment provides a method for preparing a Li2CO3 / LiCoO2 heterojunction composite material (LiCoO2 content 1 wt%), which differs from Example 1 only in that the mass of Co(NO3)2·6H2O added in step 2 is 0.049 g.

[0042] Example 3 This embodiment provides a method for preparing a Li2CO3 / LiCoO2 heterojunction composite material (LiCoO2 content 5 wt%), which differs from Example 1 only in that the mass of Co(NO3)2·6H2O added in step 2 is 0.243 g.

[0043] Example 4 This embodiment provides a method for preparing a Li2CO3 / LiFeO2 heterojunction composite material (LiFeO2 content 3 wt%), which differs from Example 1 only in that 0.151 g of Fe(NO3)3·9H2O is added in step 2 instead of Co(NO3)2·6H2O, and the remaining steps are the same as in Example 1.

[0044] Example 5 This embodiment provides a method for preparing a Li2CO3 / LiNiO2 heterojunction composite material (LiNiO2 content 3 wt%), which differs from Example 1 only in that 0.148 g of Ni(NO3)2·6H2O is added in step 2 instead of Co(NO3)2·6H2O, and the remaining steps are the same as in Example 1.

[0045] Example 6 This embodiment provides a Li2CO3 / Li(Fe) 0.5 Ni0.5 The preparation method of O2 heterojunction composite material (composite oxide content 3wt%) differs from that of Example 1 only in that 0.076 g Fe(NO3)3·9H2O and 0.074 g Ni(NO3)2·6H2O are added in step 2 to replace Co(NO3)2·6H2O, and the remaining steps are the same as those in Example 1.

[0046] Example 7 This embodiment provides a method for preparing a Li2CO3 / LiMnO2 heterojunction composite material (LiMnO2 content 3 wt%), which differs from Example 1 only in that 0.143 g of Mn(NO3)2·4H2O is added in step 2 instead of Co(NO3)2·6H2O, and the remaining steps are the same as in Example 1.

[0047] Comparative Example 1 This comparative example provides Li2CO3 that has only undergone recrystallization. The specific method is as follows: commercial Li2CO3 is dissolved in deionized water at 3°C ​​by stirring, and insoluble impurities are removed by low-temperature filtration; the filtrate is slowly heated to 80°C to precipitate Li2CO3, which is then filtered while hot, the crystals are washed with hot water, and finally dried at 120°C to obtain high-purity recrystallized Li2CO3.

[0048] Comparative Example 2 This comparative example provides a physically mixed Li2CO3 / LiCoO2 composite material, which differs from Example 1 in that: recrystallized Li2CO3 and commercial LiCoO2 (purchased from Aladdin) are physically mixed by simple grinding at a mass ratio of 97:3, without recrystallization and heat treatment steps.

[0049] Materials characterization and electrochemical performance testing 1. Morphology and Structure Characterization: The samples prepared in Example 1 were characterized by SEM and TEM. SEM images ( Figure 1 The results show that the obtained material particles are in the nanometer range (approximately 500 nm) and uniformly distributed. HRTEM image ( Figure 2 The image clearly shows the heterojunction interface where the Li2CO3 and LiCoO2 phases are in close contact, with clear lattice fringes, confirming the successful construction of the heterojunction.

[0050] 2. Half-cell performance testing: Samples from Example 1 and Comparative Example 1 were mixed with a conductive agent and a binder, respectively, to form positive electrode sheets. Using lithium metal as the counter electrode, CR2025 coin cell half-cells were assembled. The half-cells were tested at 0.1C (1C = 725 mA g). -1 The first charge-discharge test was conducted under the following conditions: voltage range 2.5-4.7V. The results are as follows: Figure 3As shown, unmodified Li2CO3 (Comparative Example 1) released almost no capacity (~12 mAh g⁻¹). -1 The Li2CO3 / LiCoO2 composite material in Example 1 exhibits a high initial charge specific capacity of 714.77 mAh g⁻¹. -1 The decomposition efficiency reached 98.60%. This indicates that the heterojunction constructed in this invention greatly promotes the electrochemical decomposition of Li2CO3.

[0051] Application Example 1: Application in Half-Cells The Li₂CO₃ / LiCoO₂ lithium supplementer prepared in Example 1 was mixed with NCM811 cathode material at a ratio of 5 wt% to form a cathode sheet (denoted as NCM811-LCO@LCO), and a half-cell was assembled using lithium metal as the counter electrode. An NCM811 cathode without the lithium supplementer was used as a comparison. The first charge-discharge test was conducted at 0.1C (first charge to 4.7V, subsequent cycles stopped at 4.3V). The results are as follows: Figure 4 As shown, the NCM811 cathode with added lithium replenishment showed an initial charge capacity increase from the original 242.38 mAh g. -1 Significantly increased to 304.58 mAh g -1 Furthermore, its main lithium release platform occurs at approximately 4.0V, which perfectly matches the operating voltage window of NCM811, demonstrating the excellent compatibility and effectiveness of this lithium replenisher in practical cathode systems.

[0052] Application Example 2: Application in Full Batteries The Li₂CO₃ / LiCoO₂ lithium supplementer prepared in Example 1 was mixed with NCM811 cathode material at a ratio of 5 wt% to form a positive electrode. The negative electrode was a Si / C@Gr composite negative electrode. An NCM811||Si / C@Gr full cell (denoted as NCM811-LCO@LCO||Si / C@Gr) was assembled, with a full cell without the lithium supplementer used as a control. Formation was performed at 0.1C, followed by long-cycle testing at 1C. The results are as follows... Figure 5 As shown, the full cell with added lithium supplementation exhibits significantly improved initial discharge capacity and energy density. After 200 cycles, its reversible capacity and capacity retention are significantly better than the full cell without added lithium supplementation, demonstrating excellent cycle stability. Specifically, the initial energy density of the full cell with added lithium supplementation is 520.72 Wh kg⁻¹. -1 Compared to the unadded group (413.84 Wh kg) -1 It is 20.53% higher, and the capacity retention rate is also higher after 200 cycles.

[0053] Performance Summary Table 1 summarizes the lithium replenishing agents of Example 1 and Comparative Example 1, as well as the performance comparison of the full cell in Application Example 2.

[0054] Table 1 As shown in Table 1, the modified lithium carbonate cathode lithium replenisher and its application provided by this invention successfully solve the problems of high decomposition potential and poor kinetics of Li2CO3 with extremely low catalyst dosage. It can effectively compensate for the first irreversible capacity loss of lithium-ion batteries, significantly improve the first coulombic efficiency, energy density and cycle life of the battery, and has extremely high industrial application prospects.

[0055] Any implementation of the technical concept, preparation process, or composite method described in this invention, which only involves conventional adjustments or optimizations to the raw material ratio and process parameters without departing from the core technical solution of this invention, shall be considered an equivalent implementation of this invention and fall within the protection scope of this invention.

Claims

1. A Li₂CO₃ / transition metal oxide heterojunction composite material, characterized in that, The transition metal oxide is LiCoO2, LiFeO2, LiNiO2, LiMnO2 or Li(Co) x Fe y Ni z Mn w O2, where x+y+z+w=1, and the mass of the transition metal oxide is 1 to 5% of the mass of Li2CO3.

2. The Li₂CO₃ / transition metal oxide heterojunction composite material according to claim 1, characterized in that, In the Li2CO3 / transition metal oxide heterojunction composite material, a heterojunction interface with close contact is formed between the transition metal oxide and Li2CO3.

3. The Li₂CO₃ / transition metal oxide heterojunction composite material according to claim 1, characterized in that, The mass of the transition metal oxide is 3% of the mass of Li2CO3.

4. The method for preparing a Li2CO3 / transition metal oxide heterojunction composite material according to claim 1, characterized in that, Includes the following steps: S1. First, dissolve commercial lithium carbonate in deionized water to obtain a lithium carbonate solution; S2. Then add a transition metal salt source to the lithium carbonate solution obtained in step S1, stir and mix evenly to obtain a mixed solution; S3. Slowly add the mixed solution obtained in step S2 into the antisolvent to precipitate the precipitate. After filtration, washing and drying, the precursor powder is obtained. S4. The precursor powder obtained in step S3 is heat-treated in an air atmosphere to obtain the Li2CO3 / transition metal oxide heterojunction composite material.

5. The preparation method according to claim 4, characterized in that, In step S2, the transition metal salt source is one or more of soluble cobalt salt, iron salt, nickel salt, and manganese salt.

6. The preparation method according to claim 5, characterized in that, The transition metal salt source is one or more of cobalt nitrate hexahydrate, ferric nitrate nonahydrate, nickel nitrate hexahydrate, and manganese nitrate tetrahydrate.

7. The application of the Li2CO3 / transition metal oxide heterojunction composite material as described in claim 1 as a positive electrode lithium supplement agent.

8. A modified lithium carbonate cathode lithium replenishing agent, characterized in that, Its composition is the Li2CO3 / transition metal oxide heterojunction composite material as described in claim 1.

9. The application of the modified lithium carbonate cathode lithium replenishing agent according to claim 8 in the preparation of cathode plates.

10. A positive electrode plate, characterized in that, It includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, wherein the positive electrode active material layer contains the modified lithium carbonate positive electrode lithium replenishing agent as described in claim 8.

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