Composite lithium supplement agent and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium supplementation agents, and particularly discloses a composite lithium supplementation agent and a preparation method and application thereof. The preparation method comprises the following steps: firstly, carrying out high-energy ball milling and mixing on a conductive agent 1, a lithium source, an oxalate-containing compound and a conductive agent 2, and carrying out thermal initiation reaction to obtain an organic lithium supplement agent A; then mixing the organic lithium supplement agent A with the inorganic lithium supplement agent B to obtain a composite lithium supplement agent; and the inorganic lithium supplement agent B is a ternary lithium-containing compound. According to the invention, advantages and disadvantages of the inorganic lithium supplement agent and the organic lithium supplement agent are complemented, the decomposition voltage of the organic lithium supplement agent is reduced, efficient lithium supplement is realized, the decomposed product is utilized to stabilize the inorganic lithium supplement agent, i.e., the crystal structure of the ternary lithium-containing compound, and subsequent side reactions are inhibited; therefore, the overall high-energy density and long-cycle stability of the battery cell are realized.

Description

Technical Field

[0001] This invention relates to the field of lithium supplementation technology, and in particular to a composite lithium supplementation agent, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in energy storage, consumer batteries, and power batteries due to their high energy density, long cycle life, and lack of heavy metal contamination. However, the formation of the SEI during the first charge and discharge process and the cycling process both result in the loss of a large number of lithium ions, leading to irreversible capacity loss and reduced cycle retention.

[0003] Electrode lithium replenishment is a key technology for alleviating the aforementioned problems and improving battery performance, with broad development prospects and application markets. However, current high-capacity lithium replenishment technologies still suffer from a critical issue: different lithium replenishing agents, such as those decomposing during delithiation, may cause the precipitation of N, O, and other groups, leading to an unstable solid-electrolyte interface, or even side reactions with the electrolyte, reducing lithium replenishment efficiency and severely affecting cell performance. For example, commonly available ternary lithium-containing compound lithium replenishing agents (including Li2NiO2, Li5FeO4, Li6CoO4, etc.) are popular choices for cathode lithium replenishment due to their high lithium replenishment capacity and good battery processing compatibility. However, the crystal structure of these materials is unstable during delithiation, potentially leading to oxygen release or side reactions with the electrolyte. Organic lithium replenishing agents (including Li2C2O4, Li2C4O4, etc.) have good air stability and leave virtually no residue after delithiation. However, these materials have high delithiation voltages, offering no lithium replenishment effect under low voltage conditions, while decomposition under high voltage conditions can lead to electrolyte oxidation and damage to the cathode material structure.

[0004] Therefore, how to provide a lithium supplement that can suppress or capture heteroatom groups generated by the lithium supplement on the positive electrode side and reduce the impact of side reactions is a problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a composite lithium replenishing agent, its preparation method and application, to solve the problems of existing lithium replenishing agents, such as unstable crystal structure, easy side reaction with electrolyte, high delithiation voltage, no lithium replenishing effect under low voltage conditions, decomposition under high voltage conditions leading to electrolyte oxidation and decomposition, and damage to the positive electrode material structure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a composite lithium supplement includes the following steps: 1) Conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 are mixed by high-energy ball milling and thermally initiated reaction to obtain organic lithium supplement A; 2) Mix organic lithium supplement A with inorganic lithium supplement B to obtain a composite lithium supplement; The inorganic lithium supplement B is a ternary lithium-containing compound.

[0007] Preferably, the conductive agent 1 in step 1) includes Ketjen black and / or conductive carbon black; The lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium oxide; The oxalate-containing compound includes one or more of oxalic acid, ammonium oxalate, and ammonium hydrogen oxalate. The conductive agent 2 includes one or more of carbon nanotubes, carbon nanofibers, and graphene.

[0008] Preferably, the mass ratio of conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 in step 1) is 1~10:10~30:70~90:1~10.

[0009] Preferably, the high-energy ball milling mixing time is 1~10h, the high-energy ball milling mixing speed is 300~600rpm, and the ball-to-material ratio of the high-energy ball milling mixing is 15~25:1.

[0010] Preferably, the particle size of the organic lithium supplement A is ≤1.5μm.

[0011] Preferably, the inorganic lithium supplement B includes one or more of lithium nickelate, lithium iron ferrite, lithium silicate, and lithium niobate.

[0012] Preferably, the mass ratio of the organic lithium supplement A to the inorganic lithium supplement B is 75~95:5~25.

[0013] Another object of the present invention is to provide a composite lithium supplement prepared by the above preparation method.

[0014] Another object of the present invention is to provide the application of composite lithium supplementation agents in the preparation of positive electrode sheets, comprising the following steps: The composite lithium supplement is mixed with the positive electrode material, binder and conductive agent, and then the mixture is slurryed. The resulting slurry is then coated onto the current collector to obtain the positive electrode sheet.

[0015] Preferably, the mass ratio of the composite lithium replenishing agent, the positive electrode material, the binder, and the conductive agent is 1~6:90.5~97.5:0.8~1.2:1.5; The cathode material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium-rich manganese.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention prepares an organic lithium supplement A through high-energy ball milling and thermally initiated reaction. High-energy ball milling helps reduce the particle size of the organic lithium supplement A, and a three-dimensional conductive agent is added to the raw materials to form a three-dimensional network structure. Simultaneously, it is mixed with an inorganic lithium supplement B to obtain a composite lithium supplement. The transition metal ions in the inorganic lithium supplement B weaken the C / C bonds of the organic lithium supplement A, further reducing its decomposition voltage to be close to the delithiation voltage of the inorganic lithium supplement B. At the same time, the organic lithium supplement A contains decomposed oxalate groups, which can reduce highly active transition metal ions to a lower valence state, thereby stabilizing the crystal structure of the inorganic lithium supplement and inhibiting oxygen evolution, thus mitigating subsequent side reactions. Furthermore, the secondary sealing process in conventional battery cell production can extract CO2 generated from the decomposition of lithium oxalate and O2 that may be generated from the decomposition of lithium nickelate, further reducing the risk of battery cell gas expansion. Moreover, the organic lithium supplement A contains decomposed oxalate groups, which can also reduce the valence state of transition metal ions in the active material, achieving the effect of stabilizing the crystal structure of the active material. This invention achieves the complementary advantages of inorganic and organic lithium replenishing agents, reduces the decomposition voltage of organic lithium replenishing agents, and achieves efficient lithium replenishment. At the same time, it utilizes the oxalic acid groups contained in the decomposed organic lithium replenishing agents to stabilize the crystal structure of inorganic lithium replenishing agents and suppress the occurrence of subsequent side reactions, thereby achieving high energy density and long cycle stability of the battery cell as a whole. Detailed Implementation

[0017] This invention provides a method for preparing a composite lithium supplement, comprising the following steps: 1) Conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 are mixed by high-energy ball milling and thermally initiated reaction to obtain organic lithium supplement A; 2) Mix organic lithium supplement A with inorganic lithium supplement B to obtain a composite lithium supplement; The inorganic lithium supplement B is a ternary lithium-containing compound.

[0018] In this invention, the conductive agent 1 mentioned in step 1) includes Ketjen black and / or conductive carbon black (super P).

[0019] In this invention, the lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium oxide.

[0020] In this invention, the oxalate-containing compound includes one or more of oxalic acid, ammonium oxalate, and ammonium hydrogen oxalate, and the oxalate-containing compound also includes the hydrates corresponding to the above compounds.

[0021] In this invention, the conductive agent 2 includes one or more of carbon nanotubes, carbon nanofibers, and graphene.

[0022] In this invention, the mass ratio of conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 in step 1) is 1~10:10~30:70~90:1~10.

[0023] In this invention, the high-energy ball milling mixing time is 1~10h, specifically 2h, 4h, 5h, 6h, or 8h; the high-energy ball milling mixing speed is 300~600rpm, specifically 350rpm, 400rpm, 450rpm, 500rpm, or 550rpm; the ball-to-material ratio of the high-energy ball milling mixing is 15~25:1, preferably 18~22:1, and more preferably 20:1.

[0024] In this invention, the particle size of the organic lithium supplement A is ≤1.5μm, specifically 0.2μm, 0.5μm, 0.6μm, 0.8μm, 1μm, 1.2μm, or 1.4μm.

[0025] In this invention, the inorganic lithium supplement B includes one or more of lithium nickelate, lithium iron ferrite, lithium silicate, and lithium niobate.

[0026] In this invention, the mass ratio of the organic lithium supplement A to the inorganic lithium supplement B is 75~95:5~25, preferably 80~90:10~20, and more preferably 85:15.

[0027] The present invention also provides a composite lithium supplement prepared by the above preparation method.

[0028] This invention also provides the application of composite lithium supplementation agents in the preparation of positive electrode sheets, including the following steps: The composite lithium supplement is mixed with the positive electrode material, binder and conductive agent, and then the mixture is slurryed. The resulting slurry is then coated onto the current collector to obtain the positive electrode sheet.

[0029] In this invention, the mass ratio of the composite lithium supplement, positive electrode material, binder and conductive agent is 1~6:90.5~97.5:0.8~1.2:1.5, preferably 2~5:92~96:0.9~1.1:1.5, and more preferably 4:95:1:1.5.

[0030] In this invention, the positive electrode material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium-rich manganese.

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] Super P (conductive carbon black), lithium hydroxide, oxalic acid, and CNT (carbon nanotubes, Tiannai, LB217-54) (super P: lithium hydroxide: oxalic acid: CNT (mass ratio) = 1:9:36:4) were mixed by high-energy ball milling. The high-energy ball milling parameters were: time 5 h, speed 500 rpm, and ball-to-material ratio 20:1. A thermally initiated reaction occurred during the high-energy ball milling process. After the reaction was completed, the solid product was added to anhydrous ethanol for washing (500 rpm, 5 min). After the washing was completed, the product was filtered and dried to obtain organic lithium supplement A with a particle size ≤1.5 μm.

[0034] The organic lithium supplement A obtained above is mixed with lithium nickelate (mixed organic lithium supplement: lithium nickelate (mass ratio) = 80:20) to obtain a composite lithium supplement.

[0035] A composite lithium supplement agent was mixed with lithium cobalt oxide, PVDF, and super P at a mass ratio of 2.5:95:1:1.5 to form a slurry. This slurry was then coated onto a current collector to obtain the positive electrode material. This material was then matched with a conventional graphite negative electrode and fabricated into a battery cell using a winding process. The separator was a porous polyethylene membrane, and the electrolyte was a 1M LiPF6 in EC / DEC / EMC solution with a volume ratio of 1:1:1.

[0036] The battery cells underwent cycling and post-cycle gas production tests, and the initial efficiency was calculated based on the cumulative capacity from the formation and capacity testing processes. The cycling test involved charging the cells at 1C constant current and constant voltage to 4.45V, with a cutoff rate of 0.02C, followed by discharging at 1C constant current to 3V, for a total of 100 cycles. The gas production test involved measuring the gas production of the cycled cells using the water displacement method; the results are shown in Table 1.

[0037] Example 2

[0038] Super P (conductive carbon black), lithium carbonate, ammonium oxalate, and CNT (same as in Example 1) (super P: lithium carbonate: ammonium oxalate: CNT (mass ratio) = 5:12:75:3) were mixed by high-energy ball milling. The high-energy ball milling parameters were: time 2 h, speed 600 rpm, and ball-to-material ratio 25:1. A thermally initiated reaction occurred during the high-energy ball milling process. After the reaction was completed, the solid product was added to anhydrous ethanol and washed (500 rpm, 5 min). After the washing was completed, the product was filtered and dried to obtain organic lithium supplement A with a particle size ≤1.5 μm.

[0039] The organic lithium supplement A obtained above is mixed with lithium nickelate (mixed organic lithium supplement: lithium nickelate (mass ratio) = 80:20) to obtain a composite lithium supplement.

[0040] A composite lithium supplement agent was mixed with lithium cobalt oxide, PVDF, and super P at a mass ratio of 2.5:95:1:1.5 to form a slurry. This slurry was then coated onto a current collector to obtain the positive electrode material. This material was then matched with a conventional graphite negative electrode and fabricated into a battery cell using a winding process. The separator was a porous polyethylene membrane, and the electrolyte was a 1M LiPF6 in EC / DEC / EMC solution with a volume ratio of 1:1:1.

[0041] The test method is the same as in Example 1, and the measurement results are shown in Table 1.

[0042] Example 3

[0043] Ketjen black, lithium hydroxide, oxalic acid, and CNT (same as in Example 1) (Ketjen black: lithium hydroxide: oxalic acid: CNT (mass ratio) = 8:25:85:8) were mixed by high-energy ball milling. The high-energy ball milling parameters were: time 8 h, speed 300 rpm, and ball-to-material ratio 18:1. A thermally initiated reaction occurred during the high-energy ball milling process. After the reaction was completed, the solid product was added to anhydrous ethanol and washed (500 rpm, 5 min). After the washing was completed, the product was filtered and dried to obtain organic lithium supplement A with a particle size ≤1.5 μm.

[0044] The above-obtained mixed organic lithium supplement is mixed with lithium nickelate (mixed organic lithium supplement: lithium nickelate (mass ratio) = 90:10) to obtain a composite lithium supplement.

[0045] A composite lithium supplement agent was mixed with lithium cobalt oxide, PVDF, and super P at a mass ratio of 2.5:95:1:1.5 to form a slurry. This slurry was then coated onto a current collector to obtain the positive electrode material. This material was then matched with a conventional graphite negative electrode and fabricated into a battery cell using a winding process. The separator was a porous polyethylene membrane, and the electrolyte was a 1M LiPF6 in EC / DEC / EMC solution with a volume ratio of 1:1:1.

[0046] The test method is the same as in Example 1, and the measurement results are shown in Table 1.

[0047] Comparative Example 1

[0048] Lithium nickel oxide, lithium cobalt oxide, PVDF, and super P were mixed and slurried in a weight ratio of 2.5:95:1:1.5, and then matched with a conventional graphite anode. The resulting slurry was then fabricated into a battery cell using a winding process. A porous polyethylene membrane was used as the separator, and a 1M LiPF6 in EC / DEC / EMC electrolyte was used in a volume ratio of 1:1:1. The testing procedures were the same as in the previous example, and the measurement results are shown in Table 1.

[0049] Table 1. Test results of Examples 1-3 and Comparative Example 1

[0050] As can be seen from Table 1, the embodiments of the present invention have higher initial efficiency and better cycle retention, and lower gas production after cycling. This shows that the mixed lithium replenishing agent is more conducive to improving lithium replenishment efficiency and lithium utilization than the single lithium replenishing agent, while suppressing the generation of side reactions, further reducing gas production and improving cycle stability.

[0051] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0052] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite lithium supplement, characterized in that, Includes the following steps: 1) Conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 are mixed by high-energy ball milling and thermally initiated reaction to obtain organic lithium supplement A; 2) Mix organic lithium supplement A with inorganic lithium supplement B to obtain a composite lithium supplement; The inorganic lithium supplement B is a ternary lithium-containing compound.

2. The method for preparing a composite lithium supplement according to claim 1, characterized in that, The conductive agent 1 mentioned in step 1) includes Ketjen black and / or conductive carbon black; The lithium source includes one or more of lithium hydroxide, lithium carbonate, and lithium oxide; The oxalate-containing compound includes one or more of oxalic acid, ammonium oxalate, and ammonium hydrogen oxalate. The conductive agent 2 includes one or more of carbon nanotubes, carbon nanofibers, and graphene.

3. The method for preparing a composite lithium supplement according to claim 2, characterized in that, In step 1), the mass ratio of conductive agent 1, lithium source, oxalate-containing compound and conductive agent 2 is 1~10:10~30:70~90:1~10.

4. The method for preparing a composite lithium supplement according to claim 3, characterized in that, The high-energy ball milling mixing time is 1~10h, the high-energy ball milling mixing speed is 300~600rpm, and the ball-to-material ratio of the high-energy ball milling mixing is 15~25:

1.

5. A method for preparing a composite lithium supplement according to any one of claims 1 to 4, characterized in that, The organic lithium supplement A has a particle size ≤1.5μm.

6. The method for preparing a composite lithium supplement according to claim 5, characterized in that, The inorganic lithium supplement B includes one or more of lithium nickelate, lithium iron ferrite, lithium silicate, and lithium niobate.

7. The method for preparing a composite lithium supplement according to claim 6, characterized in that, The mass ratio of the organic lithium supplement A to the inorganic lithium supplement B is 75~95:5~25.

8. The composite lithium supplement prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the composite lithium supplement agent according to claim 8 in the preparation of positive electrode sheets, characterized in that, Includes the following steps: The composite lithium supplement is mixed with the positive electrode material, binder and conductive agent, and then the mixture is slurryed. The resulting slurry is then coated onto the current collector to obtain the positive electrode sheet.

10. The application of the composite lithium supplement agent according to claim 9 in the preparation of positive electrode sheets, characterized in that, The mass ratio of the composite lithium supplement, positive electrode material, binder, and conductive agent is 1~6:90.5~97.5:0.8~1.2:1.5; The cathode material includes one or more of lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium-rich manganese.

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