Search

EP-4579771-B1 - POSITIVE ELECTRODE ACTIVE MATERIAL AND LITHIUM-ION BATTERY

EP4579771B1EP 4579771 B1EP4579771 B1EP 4579771B1EP-4579771-B1

Inventors

  • LIU, GANG
  • LIU, Shihao
  • SHI, Zhongyang
  • LIU, Fanfen
  • YUAN, Dingding

Dates

Publication Date
20260513
Application Date
20240711

Claims (6)

  1. A positive electrode active material, comprising lithium iron phosphate coated with a carbon layer, and an I D /I G value of the positive electrode active material is 0.75-1.2, wherein a peak intensity at a wave length of 1360 cm -1 is considered as I D , and a peak intensity at a wave length of 1580 cm -1 is considered as I G in a Raman spectrum of the positive electrode active material, the Raman testing being conducted as specified in the description; wherein a method of preparing the positive electrode active material comprises following steps: ball-milling a mixture of a FePO4 precursor, a lithium source, a carbon source, and a dispersant, and sintering to prepare the positive electrode active material; wherein the carbon source comprises the glucose and the polyethylene glycol, wherein a mass ratio of the glucose to the polyethylene glycol is (0.6-1.2):1.
  2. The positive electrode active material according to claim 1, wherein the I D /I G value of the positive electrode active material is 0.8-1.0.
  3. The positive electrode active material according to claim 1, wherein a thickness of the carbon layer is 2-6 nm.
  4. The positive electrode active material according to claim 1, wherein the FePO 4 precursor comprises at least one of FePO 4 and FePO 4 coated with a carbon source.
  5. The positive electrode active material according to claim 1, wherein a temperature of the sintering is 680- 720°C.
  6. A lithium-ion battery, comprising a positive electrode active material as claimed in claims -5 .

Description

Field The present disclosure relates to the technical field of batteries and, particularly, to a positive electrode active material and a lithium-ion battery. Background Lithium iron phosphate is widely used as positive electrode material for lithium-ion batteries due to its wide range of raw material sources, high theoretical specific capacity, stable voltage platform, good safety performance and low cost. However, the electronic conductivity of LiFePO4 is relatively small at about 10-9 S/cm. Moreover, its olivine structure has only one-dimensional Li+ diffusion channels, and the diffusion of Li+ is hindered when the material structure is changed or the LiFePO4 surface is blocked by impurities, resulting in low Li+ diffusion coefficients (about 10-14-10-16 cm2/s at room temperature), which is especially serious at low temperatures. In order to improve the electrical conductivity and low-temperature performance of LiFePO4, the commonly used methods are: (1) doping high-valent ions or metal oxides to increase the intrinsic conductivity of the material; (2) reducing the particle size to shorten the diffusion distance of Li+; and (3) employing carbon coating or coating other conductive substances on the surface of the LiFePO4 material to increase the surface electrical conductivity of the material. However, the increased diffusion rate of Li+ does not significantly improve the low-temperature performance of LiFePO4. As Li+ transfer at the interface is a rate-determining step in the LiFePO4 electrode reaction compared to diffusion within the stereoscopic phase, the relatively poor low-temperature performance originates from the slow Li+ transfer process at the interface between the electrode and the electrolyte. EP3614466 B1, EP3799159 A1, EP3301741 A1 discloses a cathode material which is coated with a carbonaceous film, and discloses a peak intensity ratio (ID/IG) between a D band and a G band in a Raman spectrum obtained by Raman spectrometry. EP3178785A1 discloses a method for manufacturing a base material powder having a carbon nanocoating layer, and discloses that the ratio of sp 2< bonds of the carbon-coated LiFePO4 can be evaluated from the ratio of peak intensities of the D peak and the G peak, I(D)/I(G). Therefore, there is an urgent need in the art for a technical scheme that promotes the transfer of Li+ at the interface between the electrode and the electrolyte, improves the electrical conductivity of LiFePO4, thereby increasing the rate performance, and improves the low-temperature performance of lithium iron phosphate positive electrode materials. Summary The present disclosure aims to solve the following technical problems: how to improve the Li+ transfer rate at the interface between the electrode and the electrolyte, and improve the electrical conductivity of lithium iron phosphate, thereby improving the rate performance, which improves the low-temperature performance of lithium iron phosphate. As a first aspect, provided in the present disclosure is a positive electrode active material, including lithium iron phosphate coated with carbon layer, and an ID/IG value of the positive electrode active material is 0.75-1.2, wherein a peak intensity at a wave length of 1360 cm-1 is considered as ID and a peak intensity at a wave length of 1580 cm-1 is considered as IG in a Raman spectrum of the positive electrode active material. A method of preparing the positive electrode active material comprises following steps: ball-milling a mixture of a FePO4 precursor, a lithium source, a carbon source, and a dispersant, and sintering to prepare the positive electrode active material; and wherein the carbon source comprises the glucose and the polyethylene glycol, wherein a mass ratio of the glucose to the polyethylene glycol is (0.6-1.2):1. As a second aspect, provided in the present disclosure is a lithium-ion battery including the positive electrode active material. In the present disclosure, the lithium-ion battery includes a positive electrode active material including the lithium iron phosphate coated with carbon layer with the ID/IG value being 0.75-1.2, which increases the desolvation (removal of solventized shell) rate of Li+ at the interface of the electrode and the electrolyte and enhances the desolvation ability, thereby increasing the electrical conductivity of lithium iron phosphate and improving the rate performance and the low-temperature performance of lithium-ion batteries including the positive electrode active material. Detailed description of the examples In the present disclosure, ID/IG value of the positive electrode active material is 0.75-1.2, which may be, but is not limited to the values listed below, such as 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1.0, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, and 1.2, and other values in the range but not listed are also applicable. ID/IG value of the lithium iron phosphate coated with carbon layer of the positive electrode active