Bimodal Cathode Material Coating for Dense Low-Impedance Batteries
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Solution Overview
Problem
Olivine-structured positive electrode materials for secondary batteries have low ionic and electronic conductivity, leading to inferior performance in low-temperature and high-rate charging and discharging, and carbon coating on the material surface weakens lithium-ion conductivity, limiting the modification of the material surface with oxides to improve interfacial ion transport.
Innovation Solution
A secondary battery positive electrode material comprising large particles (≥2 μm) with and without carbon coating, and small particles (≤1 μm) with a carbon coating, along with an oxide coating on some large particles to form fast ion conductors, enhancing electron and ion transport pathways.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the particle size is reduced to micron and nanometer levels to improve ionic and electronic conductivity, then charging and discharging performance is improved, but compaction density deteriorates
Solution Approach 1:
The patent segments the positive electrode material into two distinct particle size ranges: small particles (≤1 μm) for high conductivity and fast charging/discharging performance, and large particles (≥2 μm) for high compaction density and energy density. This segmentation allows each size fraction to fulfill its specific functional role.
Solution Approach 2:
The patent changes the particle size parameter to create a bimodal distribution with specific cutoff points (≤1 μm and ≥2 μm). By controlling the particle size parameter within these ranges and optimizing the proportion of each size fraction, the patent achieves both improved conductivity and maintained compaction density.
2Reliability
If oxide coating is applied to improve interfacial ion transport, then lithium-ion conductivity is improved, but the process cannot be completed simultaneously with carbon coating due to conflicting process conditions
Solution Approach 1:
The patent segments the coating application process by applying carbon coating and oxide coating to different particle size fractions separately. Small particles receive carbon coating while large particles receive oxide coating, allowing each coating process to be optimized for its specific material and process requirements without interference.
Solution Approach 2:
The patent uses particle size as an intermediary criterion to differentiate which coating process is applied to which particles. This intermediary classification enables the separation of conflicting coating processes and allows both carbon and oxide coatings to be applied under their respective optimal conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves compaction density and reduces impedance, balancing kinetic performance and energy density by stabilizing electron pathways and ion conductivity, resulting in higher energy density and lower impedance in secondary batteries.
Implementation Method 1
The surface of the small positive electrode material particles with a particle size of ≤1 μm is coated with a carbon layer, which partially serves as a conductive agent. This coating surrounds the large particles with a particle size of ≥2 μm in the electrode, maintaining stable electron pathways during charge-discharge cycles and providing sufficient electron transport paths
Implementation Method 2
at least some of the large particles have an oxide coating. The oxide coating and doping of large particle positive electrode materials with a particle size ≥2 μm can form fast ion conductors or fine-tune the material's lattice, thereby enhancing the interfacial and bulk ion transport rates of large particles
Implementation Method 3
The present invention improves the compaction density of the positive electrode material through a size distribution of large and small particles. By using large particles with a particle size of ≥2 μm and small particles with a particle size of ≤1 μm, it can achieve the effect of small particles filling the gaps between large particles, thereby increasing the compaction density
Data Source
AI summary
A secondary battery positive electrode material, relating to the field of battery materials. The secondary battery positive electrode material comprises large particles with particle size of ≥2 μm and small particles with particle size of ≤1 μm. The surfaces of some of the small particles are provided with a carbon coating layer; and the surfaces of some of the large particles are not provided with a carbon coating layer. According to the positive electrode material, by means of gradation design of the large and small particles, the compaction density is improved. Moreover, the surfaces of the small particles are coated with a carbon layer to provide sufficient electron transport paths. Additionally, the surfaces of the large particles are not hindered by a carbon coating layer, so that the impedance in a charge and discharge process can be reduced.