Dry-method lithium supplement positive electrode material and preparation method thereof, positive electrode membrane and preparation method thereof, and lithium ion battery

Abstract

The invention discloses a dry-method lithium supplement positive electrode material and a preparation method thereof, a positive electrode membrane and a preparation method thereof, and a lithium ion battery, and belongs to the technical field of lithium batteries. The dry-method lithium supplement positive electrode material comprises a positive electrode active material, a conductive additive, a polymer binder and Li6WO6, based on 100% of the total mass of the positive electrode active material, the conductive additive and the polymer binder, the mass percentage of the positive electrode active material is 80-85%; the mass percent of the conductive additive is 5-10%; the mass percent of the polymer binder is 0.5-5%; and the mass of Li6WO6 is 5-9% of the total mass of the positive electrode active material, the conductive additive and the polymer binder. When the dry-method lithium supplementing positive electrode material is used for carrying out dry-method lithium supplementing on a lithium ion battery, Li6WO6 is not easy to bond and agglomerate, the stability is high, and the lithium supplementing effect is good; the lithium ion battery containing the dry-method lithium supplement positive electrode material has excellent cycling stability and high first-circle specific capacity.

Description

Dry-process lithium-ion cathode materials and their preparation methods, cathode electrode films and their preparation methods, lithium-ion batteries. Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a dry-process lithium-added cathode material and its preparation method, a cathode electrode film and its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, electronic devices, and smart networks due to their high energy density, long cycle life, and portability. However, during the initial activation of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the negative electrode surface, forming a solid electrolyte interphase (SEI) film. This permanently consumes a large amount of lithium from the positive electrode, resulting in a low coulombic efficiency (ICE) for the first cycle. Furthermore, numerous side reactions inevitably occur during battery cycling, further depleting lithium ions and reducing the battery's capacity and energy density.

[0003] Currently, the main approach to reducing lithium-ion consumption is through pre-lithiation technology. This involves adding lithium ions before the lithium-ion battery is cycled to offset irreversible lithium loss caused by SEI film formation and side reactions, thereby increasing the battery's energy density. Pre-lithiation technology primarily includes positive electrode lithium replenishment and negative electrode lithium replenishment. Compared to lithium powder or lithium foil commonly used for negative electrode lithium replenishment, positive electrode lithium replenishment is less demanding in terms of environmental requirements and has significantly lower costs. A small amount of lithium replenishment can be added directly during the positive electrode component mixing process, making it more suitable for current production technologies. Currently, most commercial positive electrode lithium replenishment additives produce inert byproducts or completely decompose into gas after achieving lithium replenishment. Inert byproducts do not contribute to the subsequent cycle performance of the material, while lithium replenishment additives that completely decompose and produce gas can create excessive cavities within the material, damaging the electrode material structure. Therefore, developing a lithium replenishment additive that provides a certain lithium replenishment capacity while also improving cycle performance with some residue is of great significance.

[0004] Meanwhile, in the current wet process for producing lithium-ion batteries, the lithium replenishing agent itself contains a large amount of lithium and is highly alkaline. The lithium replenishing agent particles are prone to agglomeration in the wet organic solvent, resulting in poor stability and seriously affecting the lithium replenishment effect. Summary of the Invention

[0005] In order to solve the problems of poor lithium replenishment effect caused by easy adhesion and poor stability of lithium replenishment agents in the existing wet lithium replenishment process mentioned in the background art, the purpose of this invention is to provide a dry lithium replenishment cathode material and its preparation method, a cathode electrode film and its preparation method, and a lithium-ion battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On the one hand, the present invention provides a dry lithium replenishment cathode material, wherein the dry lithium replenishment cathode material includes a cathode active material, a conductive additive, a polymer binder, and a cathode lithium replenishment agent Li6WO6;

[0007] Based on the total mass of the positive electrode active material, conductive additives, and polymer binder (100%), the positive electrode active material comprises 80-85% by mass; the conductive additives comprise 5-10% by mass; and the polymer binder comprises 0.5-5% by mass.

[0008] The mass of the positive electrode lithium supplement Li6WO6 is 5-9% of the total mass of the positive electrode active material, conductive additive, and polymer binder.

[0009] It should be noted that the mass percentage of the positive electrode active material is 80-85%, for example, it can be 80%, 81%, 82wt%, 83%, 84%, 85%, or any content within this range. If the mass percentage of the positive electrode active material is less than 80%, it will lead to a reduction in battery capacity, resulting in a lower overall energy density and failure to meet energy requirements; if the mass percentage of the positive electrode active material is greater than 85%, it will be detrimental to the cycle stability of the battery.

[0010] The conductive additive has a mass percentage of 5-10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, or any content within this range. If the mass percentage of the conductive additive is less than 5%, a complete conductive network cannot be formed, which is not conducive to the transport of electrons / ions and cannot fully utilize the capacity of the electrode material; if the mass percentage of the conductive additive is greater than 10%, it will result in a lower overall energy density of the battery.

[0011] The polymer adhesive has a mass percentage of 0.5-5%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any content within this range. Within this range, it has a good bonding effect.

[0012] The mass of the positive electrode lithium replenishing agent Li6WO6 is 5-9% of the total mass of the positive electrode active material, conductive additives, and polymer binder, for example, it can be 5%, 6%, 7%, 8%, 9%, or any content within this range. If it is less than 5%, the lithium replenishing agent is too insufficient to effectively compensate for the lithium ions consumed in the formation of the SEI layer and side reactions; if it is more than 9%, it will lead to an imbalance in the internal chemical reaction of the battery, increasing the probability of the battery overheating, short circuits, and other problems.

[0013] Furthermore, Li6WO6 is used to replenish lithium in the positive electrode, offsetting the irreversible lithium loss caused by the formation of the SEI film and side reactions, thereby improving the energy density of the battery.

[0014] Furthermore, the positive electrode active material includes lithium cobalt oxide, Li... 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 (LRMO), LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 (NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2 (NCM811).

[0015] Further, the conductive additive includes at least one selected from acetylene black, Super P, Ketjen black, MXenes, and graphene. Preferably, the conductive additive is at least one selected from Ketjen black and graphene.

[0016] Furthermore, the conductive additive is used to form a complete conductive network in the dry lithium-filled cathode material, improve electron / ion transport efficiency, and thus improve the capacity of the dry lithium-filled cathode material.

[0017] Further, the polymer binder includes at least one selected from polytetrafluoroethylene, polyacrylic acid, polyvinylpyrrolidone, carboxymethyl cellulose, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluoroethylene, sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium carboxyethyl cellulose, carboxymethyl ethyl cellulose, and carboxypropyl methyl cellulose. Preferably, the polymer binder is at least one selected from polytetrafluoroethylene, sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium carboxyethyl cellulose, carboxymethyl ethyl cellulose, and carboxypropyl methyl cellulose.

[0018] On the other hand, the present invention provides a method for preparing any of the above-described dry-process lithium-added cathode materials, comprising the following steps:

[0019] The positive electrode active material, conductive additive, and positive electrode lithium supplement Li6WO6 are mixed to obtain a mixture;

[0020] The mixture is kept at 130-170℃ for 20-60 minutes, and then a polymer binder is added and mixed evenly to obtain the dry lithium-filled cathode material.

[0021] Furthermore, the polymer binder forms a three-dimensional network structure through fiber fibrillation, which binds and aggregates the positive electrode active material and conductive additives coated with Li6WO6.

[0022] Further, the mixture is homogenized with the polymer binder at 130-170°C, for example, the temperature can be 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, or any temperature within this range. Within this temperature range, the polymer binder is more easily fibrous and has a better bonding effect. The mixing time is 10-60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any time within this range.

[0023] On the other hand, the present invention provides a positive electrode film comprising any of the dry lithium-filling positive electrode materials described above or the dry lithium-filling positive electrode materials prepared by the preparation methods described above, and a current collector.

[0024] Furthermore, the current collector comprises carbon-coated aluminum foil.

[0025] Furthermore, the thickness of the positive electrode film is 100-200 μm, for example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any thickness within this range. If the thickness of the positive electrode film is less than 100 μm, the loading of the positive electrode active material is low, resulting in low energy density of the battery; if the thickness of the positive electrode film is greater than 200 μm, the charge transport distance and resistance increase, the transport dynamics are poor, and ultimately the rate performance of the battery deteriorates and the capacity is low.

[0026] In another aspect, the present invention provides a method for preparing any of the above-described positive electrode films, comprising the following steps:

[0027] The dry lithium-filling cathode material prepared by any of the above-described dry lithium-filling cathode materials or by the above-described preparation methods is rolled into sheets.

[0028] The sheet and the current collector are bonded together to obtain the positive electrode film.

[0029] Further, the calendering temperature is 20-150°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any temperature within this range; and the calendering temperature is lower than the glass transition temperature of the selected polymer binder. The calendering time is 10-60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any time within this range.

[0030] Furthermore, the number of rolling cycles is 10-20 times, for example, 10, 12, 15, 16, 18, 20 times, or any number within this range; the time interval between two rolling cycles is 5-10 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, or any time interval within this range. Within this range, the dry-process lithium-ion cathode material sheet exhibits high compaction density and excellent flexibility.

[0031] Furthermore, the bonding temperature is 100-150℃, for example, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, or any temperature within this range; the bonding time is 10-60 minutes, such as 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, or any time within this range. Within this range, the lithium-ion cathode material sheet and the current collector exhibit excellent adhesion and high interfacial stability.

[0032] In another aspect, the present invention provides a lithium-ion battery comprising any of the dry-process lithium-replenishing cathode materials described above, or dry-process lithium-replenishing cathode materials prepared by any of the preparation methods described above, or cathode electrode films described above, or cathode electrode films prepared by any of the preparation methods described above.

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

[0034] (1) The dry lithium replenishment cathode material of the present invention is used to perform dry lithium replenishment on lithium-ion batteries without the need for solvents. Li6WO6 is not easy to agglomerate and has high stability, resulting in good lithium replenishment effect.

[0035] (2) The Li6WO6 positive electrode lithium replenishing agent used in this invention can coat the surface of the positive electrode active material to form protection after cycling, thereby improving the interfacial ion conduction ability between the positive electrode and the electrolyte.

[0036] (3) The positive electrode film prepared by the present invention avoids the precipitation of active material caused by diffusion and capillary effect during solvent evaporation, which leads to crack generation and electrode peeling.

[0037] (4) The positive electrode film of the present invention has excellent flexibility and compaction density, and high energy density.

[0038] (5) The polymer binder used in this invention is easy to fibrous and can form a continuous bonding network during the mixing process, effectively connecting the positive electrode active material and conductive additives coated by Li6WO6, so that the dry lithium replenishment positive electrode material and the current collector have excellent adhesion and high stability.

[0039] (6) The lithium-ion battery containing the dry lithium replenishment cathode material of the present invention has excellent interface stability, excellent cycle stability, high capacity and high first-cycle specific capacity. Attached Figure Description

[0040] Figure 1 shows the charge-discharge cycle test diagram of the lithium-ion batteries prepared by the dry-method lithium-replenishing cathode materials provided in Examples 1, 3, 4, Comparative Examples 1, 3, 5, 6, 7, and 8 of this invention.

[0041] Figure 2 shows the charge-discharge cycle test diagrams of lithium-ion batteries prepared by dry-method lithium-added cathode materials provided in Examples 2, 2, and 4 of this invention.

[0042] Figure 3 shows the positive electrode active material Li after 80 cycles of the lithium-ion battery prepared by the dry lithium replenishment positive electrode material provided in Example 1 of the present invention. 1.2 Mn 0.54 Ni 0.13 Co 0.13 SEM image (top) and EDS image (bottom) of O2. Detailed Implementation

[0043] To better understand the content of this invention, the following detailed description is provided in conjunction with specific implementation methods. However, the scope of protection of this invention is not limited to the following embodiments.

[0044] In the following examples and comparative examples, abbreviations are used to represent the corresponding compounds, as follows:

[0045] LRMO is Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2,

[0046] NCM811 is for LiNi 0.8 Co 0.1 Mn 0.1 O2,

[0047] LWO is Li6WO6.

[0048] LFO is Li5FeO4.

[0049] LNO is Li2NiO2

[0050] CMC stands for carboxymethyl cellulose.

[0051] Example 1

[0052] Preparation of dry lithium-ion cathode material: 1700 mg of LRMO, 180 mg of LWO and 200 mg of Ketjen black were ground evenly in an agate mortar to obtain a mixture; then the mixture was placed in a forced-air oven and heated to 150 °C in an air atmosphere and held for 30 min; then 100 mg of polytetrafluoroethylene (PTFE) was added and stirred evenly to obtain the dry lithium-ion cathode material.

[0053] Preparation of the positive electrode film: The dry-process lithium-ion cathode material was placed in a rolling mill and rolled for 30 minutes at a hot rolling speed of 2.0 r / min and a hot rolling temperature of 60℃. The rolling was repeated 15 times with a 10-s interval between two rolling cycles to obtain a sheet with a thickness of 100 μm. At a temperature of 150℃ and a pressure of 15 MPa, the sheet and a 25 μm thick carbon-coated aluminum foil were tightly bonded together by hot pressing with a metal disc for 30 minutes to obtain the LRMO@LWO positive electrode film.

[0054] Example 2

[0055] The difference between Example 2 and Example 1 is that the positive electrode active material is replaced with NCM811 instead of LRMO; all other aspects are the same as in Example 1. Example 2 yielded an NCM811@LWO positive electrode film.

[0056] Example 3

[0057] The difference between Example 3 and Example 1 is that the amount of LWO used is 100mg, while the rest is the same as in Example 1.

[0058] Example 4

[0059] The difference between Example 4 and Example 1 is that the amount of LWO used is 140 mg, while the rest is the same as in Example 1.

[0060] Comparative Example 1

[0061] The difference between the comparative example and Example 1 is that there is no LWO, and everything else is the same as Example 1.

[0062] Comparative Example 2

[0063] The difference between the comparative example and Example 2 is that LWO is absent; otherwise, they are the same as in Example 2.

[0064] Comparative Example 3

[0065] The difference between the comparative example and Example 1 is that the positive electrode lithium replenisher is replaced with LFO instead of LWO, and all other aspects are the same as in Example 1.

[0066] Comparative Example 4

[0067] The difference between the comparative example and Example 2 is that the positive electrode lithium replenisher is replaced with LFO instead of LWO, and all other aspects are the same as in Example 2.

[0068] Comparative Example 5

[0069] The difference between Comparative Example 5 and Example 1 is that LNO was used instead of LWO as the positive electrode lithium replenisher, while the rest were the same as in Example 1.

[0070] Comparative Example 6

[0071] The difference between Comparative Example 6 and Example 1 is that the positive electrode lithium replenishing agent is replaced with Li2O instead of LWO, and the rest is the same as Example 1.

[0072] Comparative Example 7

[0073] The difference between Comparative Example 7 and Example 1 is that the positive electrode lithium replenisher is replaced with Li2S instead of LWO, and all other aspects are the same as in Example 1.

[0074] Comparative Example 8

[0075] The difference between Comparative Example 8 and Example 1 is that the positive electrode lithium replenishing agent is replaced with Li3N instead of LWO, and all other aspects are the same as in Example 1.

[0076] Lithium-ion batteries were prepared using the positive electrode films prepared in Examples 1-4 and Comparative Examples 1-8, respectively, as detailed below:

[0077] The positive electrode films prepared in Examples 1-4 and Comparative Examples 1-8 were cut into positive electrode sheets with a diameter of 10 mm and a thickness of 120 μm, and then vacuum dried at 150 °C for 12 h.

[0078] The positive electrode sheet and the areal loading are 13.5 mg / cm². 2The graphite anode is separated by a 25 μm thick Gelgard 2400 membrane (polypropylene). A 1 mol / L lithium hexafluorophosphate (LiPF6) solution is used as the electrolyte. The solvent for the lithium hexafluorophosphate solution is a mixed solvent of fluoroethylene carbonate (EC), methyl trifluoroethyl carbonate (FEMC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), with a volume ratio of EC:2:6. The battery is assembled in an argon-filled glove box. The assembled battery is then pressurized to 50 MPa under a hydraulic press to obtain a coin-type lithium-ion battery.

[0079] The positive electrode electrochemical performance of the above-mentioned batteries was tested.

[0080] The test voltage window for Examples 1, 3, 4, Comparative Examples 1, 3, 5, 6, 7, and 8 was 2-4.7V. Continuous charge-discharge tests were conducted at a rate current of 0.5C. The test results are shown in Figure 1 and Table 1.

[0081] The test voltage window for Examples 2, 2, and 4 was 2.8-4.3V. Continuous charge-discharge tests were performed at a rate current of 0.5C. The test results are shown in Figure 2 and Table 2.

[0082] The positive electrode active material Li, prepared by the dry-method lithium-added positive electrode material provided in Example 1, after 80 cycles, 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 was imaged using a scanning electron microscope (SEM), and the distribution of tungsten on its surface was observed using energy-dispersive X-ray spectroscopy (EDS). The results are shown in Figure 3.

[0083] Table 1 Electrochemical performance test data

[0084]

[0085] Table 2 Electrochemical performance test data

[0086]

[0087] As shown in Figure 1 and Table 1, the addition of LWO cathode lithium supplement improves the 0.5C first-cycle coulombic efficiency of the dry-process battery. Compared with the absence of cathode lithium supplement, the first-cycle specific capacity increases by 21.9%, and the capacity retention after 80 cycles increases by 43.84%, demonstrating good cycle stability. Furthermore, compared with LFO, LNO, Li₂O, Li₂S, and Li₃N lithium supplements, the addition of LWO lithium supplement significantly improves the first-cycle specific capacity, 0.5C first-cycle coulombic efficiency, and capacity retention after 80 cycles.

[0088] As shown in Figure 2 and Table 2, the addition of LWO cathode lithium supplement improves the 0.5C first-cycle coulombic efficiency of the dry-process battery. Compared with the absence of cathode lithium supplement, the first-cycle specific capacity increases by 11.75%, and the capacity retention after 250 cycles increases by 24.11%, demonstrating good cycle stability. Compared with LFO lithium supplement, the addition of LWO lithium supplement significantly improves the first-cycle specific capacity, 0.5C first-cycle coulombic efficiency, and capacity retention after 250 cycles.

[0089] In summary, the addition of LWO cathode lithium replenisher significantly improved the battery's first-cycle specific capacity, indicating that the addition of the cathode lithium replenisher effectively compensated for the lithium ions consumed in the formation of the SEI layer and side reactions, which is beneficial to capacity utilization. At the same time, it formed a better cathode-electrolyte interface on the surface, reducing the consumption of side reactions and improving the overall coulombic efficiency, thereby improving the battery's cycle stability.

[0090] The above description is only a specific embodiment of the present invention and not all embodiments. Any equivalent modifications made by those skilled in the art to the technical solutions of the present invention by reading the present invention specification shall be covered by the claims of the present invention.

Claims

1. A dry-process lithium-ion cathode material, characterized in that, The dry-process lithium-added cathode material includes a cathode active material, a conductive additive, a polymer binder, and a cathode lithium supplement agent Li6WO6; based on 100% of the total mass of the cathode active material, conductive additive, and polymer binder, the mass percentage of the cathode active material is 80-85%; the mass percentage of the conductive additive is 5-10%; the mass percentage of the polymer binder is 0.5-5%; and the mass percentage of the cathode lithium supplement agent Li6WO6 is 5-9% of the total mass of the cathode active material, conductive additive, and polymer binder.

2. The dry-process lithium-filled cathode material according to claim 1, characterized in that, The positive electrode active material includes lithium cobalt oxide, Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

3. The dry-process lithium-filled cathode material according to claim 1, characterized in that, The conductive additive includes at least one of acetylene black, Super P, Ketjen black, MXenes, and graphene.

4. The dry-process lithium-filled cathode material according to claim 1, characterized in that, The polymer binder includes at least one of polytetrafluoroethylene, polyacrylic acid, polyvinylpyrrolidone, carboxymethyl cellulose, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluoroethylene, sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium carboxyethyl cellulose, and carboxymethyl ethyl cellulose.

5. The method for preparing the dry-process lithium-added cathode material according to any one of claims 1-4, characterized in that, Includes the following steps: The positive electrode active material, conductive additive, and positive electrode lithium supplementing agent Li6WO6 are mixed to obtain a mixture; the mixture is kept at 130-170℃ for 20-60 minutes, and then a polymer binder is added and mixed evenly to obtain the dry lithium supplementing positive electrode material.

6. A positive electrode film, characterized in that, Includes the dry lithium-filled cathode material according to any one of claims 1-4 or the dry lithium-filled cathode material prepared by the preparation method according to claim 5, and a current collector.

7. The positive electrode film according to claim 6, characterized in that, The current collector includes carbon-coated aluminum foil.

8. The method for preparing the positive electrode film according to any one of claims 6-7, characterized in that, The process includes the following steps: rolling the dry lithium-filling cathode material according to any one of claims 1-4 or the dry lithium-filling cathode material prepared by the preparation method according to claim 5 into a sheet; bonding the sheet and the current collector together to obtain the cathode electrode film.

9. The preparation method according to claim 8, characterized in that, The calendering temperature is 20-150°C, and the calendering temperature is lower than the glass transition temperature of the polymer adhesive; the calendering time is 10-60 min; and / or, the bonding temperature is 100-150°C, and the bonding time is 10-60 min.

10. A lithium-ion battery, characterized in that, Includes the dry lithium-filled cathode material according to any one of claims 1-4, or the dry lithium-filled cathode material prepared by the preparation method according to claim 5, or the cathode electrode film according to any one of claims 6-7, or the cathode electrode film prepared by the preparation method according to any one of claims 8-9.

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