Pulverized Nickel-Rich Cathodes With Phosphate Coating for Cycle Life
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Solution Overview
Problem
Nickel-rich cathode materials in lithium-ion batteries face issues such as cycle life reduction, air instability, and surface degradation due to particle fracture and residual lithium compound formation, limiting their practical capacity and stability, despite efforts like doping and surface modification.
Innovation Solution
Pulverizing the LiNi0.9Mn0.5Al0.05O2 cathode material and applying a lithium phosphate coating to create a bimodal cathode material, which combines pristine and coated particles in specific ratios, enhancing air stability and cycle life by preventing particle fracture and surface degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel-rich cathode materials are used to replace cobalt, then cost is reduced and capacity is increased, but cycle life is reduced due to particle fracture and surface degradation
Solution Approach 1:
The cathode material is divided into a bimodal distribution of particle sizes: intact secondary particles (10-20 μm) and mechanically pulverized primary particles (1-5 μm). This segmentation allows the intact particles to maintain structural stability and resist fracture, while the pulverized particles provide high capacity active sites, resolving the contradiction between capacity and cycle life
Solution Approach 2:
Mechanical pulverization is performed in advance on a portion of the cathode material to create fine primary particles before electrode assembly. This preliminary action ensures that high-capacity sites are prepared beforehand, and when combined with intact particles, prevents subsequent fracture during cycling by distributing mechanical stress
2Power
If high voltage cycling is applied to achieve high capacity, then discharge capacity is increased, but particle fracture and surface degradation accelerate
Solution Approach 1:
Intact secondary particles are mixed with pulverized primary particles to create a cushioning effect. During high voltage cycling, the intact particles absorb and distribute mechanical stress, preventing fracture of the pulverized particles and protecting surface integrity while maintaining high discharge capacity
3Power
If mechanical pulverization is applied to increase capacity, then discharge capacity is improved, but particle fracture occurs during cycling
Solution Approach 1:
The invention merges pulverized particles (high capacity) with intact particles (high stability) into a bimodal composite structure. The intact particles act as structural scaffolds that prevent fracture of pulverized particles during cycling, while both contribute to high discharge capacity, resolving the contradiction between capacity enhancement and particle integrity
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
The bimodal cathode material retains at least 50% capacity after 100 cycles, significantly improving cycle life and stability compared to traditional nickel-rich cathode materials, with the coated particles showing delayed voltage decay and doubled discharge capacity during high-voltage cycling.
Implementation Method 1
applying a coating on the pulverized NMA cathode material resulting in a coated pulverized NMA cathode material
Implementation Method 2
surface modification via intentional electrolyte additive decomposition
Implementation Method 3
Particle fracture is induced between weakly bound primary particles (i.e., NMA cathode material particles with a size of approximately 10 μm, or greater than about 3 μm) in the secondary particle (i.e., NMA cathode material particles with a size of less than approximately 1 μm) structure due to anisotropic lattice expansion/contraction during lithiation/delithiation
Implementation Method 4
This overlap causes oxygen to be released from the TM oxide structure when Li1-xCoO2 is delithiated beyond 50% (i.e., x>0.5) when charging, thus limiting its practical capacity to about 140 mAh/g
Data Source
AI summary
The present disclosure relates to mitigation strategies to limit particle fracture and surface degradation caused by air instability. Some embodiments include cobalt-free nickel-rich NMA (LiNi0.9Mn0.5Al0.05O2) being ball-milled to effectively “pre-crack” the secondary particles into their primary constituents or single crystallites. These NMA particles may be coated with lithium phosphate and/or phosphoric acid. After approximately 100 cycles, these pulverized NMA particles showed delay voltage decay and approximately double the discharge capacity compared to traditional pristine NMA cathode materials during high-voltage cycling.