Negative electrode based on niobium-titanium-oxygen primary particles and lithium battery

Abstract

The invention provides a negative electrode based on niobium-titanium-oxygen primary particles and a lithium battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, the negative electrode active material comprises graphite and niobium-titanium-oxygen, and the conductive agent comprises a conductive agent and a binder. The niobium-titanium-oxygen is primary particles, and the niobium-titanium-oxygen primary particles can be filled into gaps of graphite or a mixture of graphite and silicon carbon, so that the compaction density of the negative electrode plate is improved, and the cohesiveness of the negative electrode plate is enhanced, thereby reducing the use amount of a binder, improving the multiplying power and low-temperature performance of a battery cell, and obviously improving the safety performance, especially the needling safety, of the battery cell.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a negative electrode sheet and a lithium battery based on niobium-titanium oxide primary particles. Background Art

[0002] Thanks to the advantages of high energy density, low maintenance cost, low self-discharge, fast charging and long life, the application scope of lithium-ion batteries has gradually expanded from consumer electronics and power tools to emerging fields such as new energy electric vehicles, electric ships, electric aircraft, robots, etc. Battery technology continues to advance in practical applications, and battery energy density continues to increase. However, the safety risks of lithium-ion batteries have greatly affected their practical applications. Thermal runaway of lithium-ion batteries is the core cause of battery safety accidents, and abuse is the main source of thermal runaway. As one of the most stringent abuse tests, lithium-ion battery needle puncture safety testing has received widespread attention in recent years.

[0003] People have adopted various solutions to improve and optimize the safety performance of batteries, including improving the thermal stability of positive and negative electrode materials and interfaces, using high thermal stability separators, optimizing the formulation of electrolytes, etc. The present invention improves the safety performance of the battery cell by adding an appropriate proportion of niobium titanium oxide materials to the negative electrode active material. + The structure is very stable during the insertion / extraction process and has a relatively high working potential (~1.6 V vs Li + / Li), which can avoid the formation of lithium dendrites and make the battery have good safety. Summary of the invention

[0004] The purpose of the present invention is to provide a negative electrode and a lithium battery based on niobium titanium oxide primary particles in view of the problem that the battery safety performance in the prior art needs to be improved.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] A negative electrode based on niobium titanium oxide primary particles comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material comprises graphite and niobium titanium oxide, and the niobium titanium oxide is a primary particle.

[0007] In the above technical solution, when the negative electrode active material is composed of graphite and niobium titanium oxide, the content of niobium titanium oxide in the negative electrode active material is 2-10wt%;

[0008] When the negative electrode active material consists of graphite, silicon carbon and niobium titanium oxide, the content of niobium titanium oxide in the negative electrode active material is 5-10wt%.

[0009] In the above technical solution, the D50 of the niobium titanium oxide primary particles is 1 to 2 μm.

[0010] In the above technical solution, by mass parts, the negative electrode active material layer includes 80 to 98 parts of negative electrode active material, 1 to 10 parts of conductive agent, and 1 to 10 parts of binder.

[0011] In the above technical solution, the conductive agent is Super P, KS6, VGCF or CNTs; the binder is CMC, SBR or PVDF.

[0012] In the above technical solution, the negative electrode is prepared by the following steps: homogenizing the negative electrode active material, conductive agent, binder and solvent, coating it on the negative electrode current collector, and drying to obtain the negative electrode.

[0013] On the other hand, the present invention further includes a lithium battery, including the negative electrode based on niobium titanium oxide primary particles, a positive electrode, a separator and an electrolyte.

[0014] In the above technical solution, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

[0015] In the above technical solution, the composition of the positive electrode active material is represented by the formula Li a Ni x Co y Mn z M (1-x-y-z) O2, where 1.0 ≤ a ≤ 1.3, 0 ≤ x < 1, 0 < y < 1, 0 ≤ z < 1, and M represents Mg, Cr, Ti, Al or Cu.

[0016] In the above technical solution, by mass parts, the negative electrode active material layer includes 70 to 98 parts of negative electrode active material, 1 to 20 parts of conductive agent, and 1 to 10 parts of binder.

[0017] In the above technical solution, the conductive agent is Super P, KS6, VGCF or CNTs; the binder is CMC, SBR or PVDF.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The niobium titanium oxide of the present invention is primary particles, and D 50 is 1 to 2 μm, with a relatively small particle size. The niobium titanium oxide primary particles of 1 to 2 μm can be filled into the gaps between graphite or the mixture of graphite and silicon carbide, improving the compaction density of the negative electrode sheet and enhancing the adhesion of the negative electrode sheet, thereby reducing the amount of binder used and improving the rate performance and low-temperature performance of the battery cell.

[0020] 2. The addition of niobium titanium oxide primary particles significantly improves the safety performance of the battery cell, especially the puncture safety. At the same time, the rate charge and discharge, low temperature, and cycle performance of the battery cell are also slightly improved.

[0021] 3. Niobium titanium oxide is added in the negative electrode slurry process without adding new processes, and the method is simple and easy. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] A lithium battery, comprising the negative electrode with high compaction density, a positive electrode, a separator and an electrolyte, wherein:

[0024] The positive electrode is prepared by the following steps: the positive electrode active material is LiNi 0.7 Co 0.1 Mn 0.2 O2, SP and CNTs as conductive agents, PVDF as binder, and NMP as positive electrode solvent. Slurry was made according to the ratio of 1wt% of conductive agent Super P, 1wt% of CNTs, 1wt% of binder, and 97wt% of positive electrode active material. The positive electrode slurry was coated in a 150mm wide manner with a surface density of 44mg / cm 2 The weight of the coating was applied on the aluminum foil and after drying, the 3 The product is rolled in a manner of rolling and then vacuum dried to remove moisture.

[0025] The negative electrode is prepared by the following steps: using a mixture of graphite, silicon carbon and niobium titanium oxide as the negative electrode active material, niobium titanium oxide as the primary particle, 50 The negative electrode slurry is 1-2 μm, SP is used as the conductive agent, CMC and SBR are used as the binder, and H2O is used as the negative electrode solvent. Slurry is made according to 2wt% of SBR, 1wt% of CMC, 2wt% of Super P, 95wt% of graphite and niobium titanium oxide (see Table 1 for the ratio of graphite and niobium titanium oxide), or 95wt% of graphite, silicon carbon and niobium titanium oxide (see Table 1 for the ratio of graphite, silicon carbon and niobium titanium oxide). The negative electrode slurry is applied on a 6μm copper foil in a width of 154mm according to the weight in Table 1 and dried at 1.6g / cm 3 The product is rolled in a manner of rolling and then vacuum dried to remove moisture.

[0026] The battery is prepared through the following steps: the positive electrode, negative electrode and separator are stacked, welded, packaged, baked and then filled with liquid. After the battery cell is formed and divided into different capacities, it is tested for low temperature, rate, cycle and needle puncture safety.

[0027] (1) Low temperature performance test

[0028] The battery was first charged to 4.20V at 1C (30A) constant current at 25±3℃, 15~90%RH, and then charged at 4.20V constant voltage until the charging current decreased to 0.05C (1.5A), and then the charging stopped. After being stored at 25℃ / 0℃ / -20℃ / -40℃ for 8h, the battery was discharged to 2.5V at 1C1A (30A) at the corresponding temperature. The results are shown in Table 1 and Table 2.

[0029] (2) Cycle test

[0030] Under the environmental conditions of 25±3℃, 15~90%RH, charge the battery to 4.20V at 1C (30A) constant current, and then charge at 4.20V constant voltage until the charging current decreases to 0.05C (1.5A). Leave for 30min. Discharge to 2.50V at 1C (30A) constant current. Leave for 30min. Repeat the above charging, discharging and leaving steps. Calculate the capacity retention rate after 500 cycles. The results are shown in Table 1 and Table 2.

[0031] (3) Rate performance test

[0032] The battery was charged to 4.20V at 1C (30A) constant current and then charged at 4.20V constant voltage at 25±3℃ and 15~90%RH until the charging current was reduced to 0.05C (1.5A). The charging was stopped. The battery was left for 30min. The battery was discharged to 2.5V at 1C (30A) / 2C (60A) / 3C (90A) / 5C (150A) respectively. The battery was left for 30min. The capacity retention rate at different rates was calculated. The results are shown in Table 1 and Table 2.

[0033] (4) Acupuncture safety test

[0034] Under the environmental conditions of 25±3℃, 15~90%RH, charge at a constant current of 1C (30A) to 4.20V, then charge at a constant voltage of 4.20V until the charging current is reduced to 0.05C (1.5A), and then stop charging. Use a high temperature resistant steel needle with a diameter of Φ3mm, the cone angle of the needle tip is 30°~60°, the surface of the needle is smooth, free of rust, oxide layer and oil, and puncture at a speed of (25±5)mm / s. The puncture position is the middle of the battery cell. The steel needle penetrates the shell and stays in the tested battery for observation for 1h. The results are shown in Tables 1 and 2.

[0035] Table 1

[0036]

[0037] As can be seen from Table 1, when different proportions of niobium titanium oxide are mixed into the negative electrode graphite, the surface density during negative electrode coating is different. As the proportion of niobium titanium oxide added increases, the average capacity of the battery cell decreases. This is because niobium titanium oxide embeds lithium during the first charge, and cannot be de-lithiumated during discharge due to the influence of the reaction potential, resulting in a reduction in reversible lithium, thereby reducing the capacity of the battery cell. It can also be seen that as the proportion of niobium titanium oxide added increases from 0 to 8%, the -40°C low-temperature discharge performance of the battery cell gradually improves, from 60.5% to 67%. The 25°C cycle performance and 25°C 5C rate discharge performance also have similar rules. For needle puncture safety, niobium titanium oxide can pass the needle puncture test when the addition amount is ≥2%, and it cannot pass the needle puncture test when the addition amount is 0 and 1%.

[0038] Table 2

[0039]

[0040] As can be seen from Table 2, when the negative electrode is a mixture of graphite and silicon-carbon, adding different proportions of niobium titanium oxide can also improve the performance of the battery cell. As the proportion of niobium titanium oxide added increases, the capacity of the battery cell decreases. However, the -40°C low-temperature discharge performance, 25°C cycle performance and 25°C 5C rate discharge performance of the battery cell are all improved. For puncture safety, the niobium titanium oxide addition amount ≥5% can pass the puncture test, and when the addition amount is 0 and 2wt%, it cannot pass the puncture test. The silicon-carbon negative electrode has a large volume expansion during the charge and discharge process, resulting in changes in the internal structure. Compared with the graphite negative electrode, its thermal stability is poor. When the negative electrode is a mixture of graphite and silicon-carbon, adding 2wt% niobium titanium oxide cannot pass the puncture test.

[0041] In the present invention, primary particles of niobium titanium oxide can be filled into the gaps of graphite or a mixture of graphite and silicon-carbon to increase the compaction density of the negative electrode sheet. If secondary particles of niobium titanium oxide are used, the compaction density of the primary particles cannot be achieved, thereby reducing the capacity of the battery. At the same time, since niobium titanium oxide does not exert its capacity in the negative electrode of the battery, when its content in the negative electrode active material is higher than 10wt%, the battery capacity will also be significantly reduced.

[0042] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode based on niobium titanium oxide primary particles, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material comprises graphite and niobium titanium oxide, and the niobium titanium oxide is a primary particle.

2. The negative electrode based on niobium titanium oxide primary particles according to claim 1, characterized in that: When the negative electrode active material is composed of graphite and niobium titanium oxide, the content of niobium titanium oxide in the negative electrode active material is 2-10wt%; When the negative electrode active material consists of graphite, silicon carbon and niobium titanium oxide, the content of niobium titanium oxide in the negative electrode active material is 5-10wt%.

3. The negative electrode based on niobium titanium oxide primary particles according to claim 1, characterized in that: The D50 of the niobium titanate primary particles is 1 to 2 μm.

4. The negative electrode based on niobium titanium oxide primary particles according to claim 1, characterized in that: In parts by mass, the negative electrode active material layer includes 80 to 98 parts of negative electrode active material, 1 to 10 parts of conductive agent and 1 to 10 parts of binder.

5. The negative electrode based on niobium titanium oxide primary particles according to claim 4, characterized in that: The negative electrode is prepared by the following steps: homogenizing the negative electrode active material, the conductive agent, the binder and the solvent, coating the slurry on the negative electrode current collector, and drying to obtain the negative electrode.

6. A lithium battery, characterized in that: The invention comprises a negative electrode based on niobium titanium oxide primary particles as claimed in claim 1, a positive electrode, a separator and an electrolyte.

7. The lithium battery according to claim 6, characterized in that The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder.

8. The lithium battery according to claim 7, characterized in that The composition of the positive electrode active material is represented by the formula Li a Ni x Co y Mn z M (1-x-y-z) O2, where 1.0 ≦ a ≦ 1.3, 0 ≦ x < 1, 0 < y < 1, 0 ≦ z < 1, and M represents Mg, Cr, Ti, Al, or Cu.

9. The lithium battery according to claim 7, characterized in that: In parts by mass, the negative electrode active material layer includes 70 to 98 parts of negative electrode active material, 1 to 20 parts of conductive agent and 1 to 10 parts of binder.

10. The lithium battery according to claim 9, characterized in that: The conductive agent in the positive electrode and the negative electrode is Super P, KS6, VGCF or CNTs; the binder is CMC, SBR or PVDF.

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