LiCoPO4 Cathode Material Composition for Capacity Retention
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Solution Overview
Problem
LiCoPO4-based lithium-ion positive electrode materials face challenges with capacity fade, limiting their discharge capacity and cycle life, despite initial improvements in rate of discharge.
Innovation Solution
A lithium-ion positive electrode material with a nominal stoichiometry of Li1+y/2Co1−x−y−z−dSizFexMyM′d(PO4)1+y/2, where M is a trivalent cation and M′ is a divalent cation, with specific ranges for y, x, z, and d, which includes modifications such as Cr, Ti, and Si to enhance discharge capacity and reduce capacity fade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoPO4 is used as the positive electrode material, then the stored energy increases (40% more than LiFePO4), but capacity fade occurs blocking further progress
Solution Approach 1:
The patent modifies the stoichiometric parameters of LiCoPO4 by controlling the Li:Co:O ratio and using non-stoichiometric compositions (e.g., Li1+xCo1-yO2 with specific x and y ranges) to optimize both energy density and capacity retention. This parameter optimization allows achieving high stored energy while minimizing capacity fade through precise compositional control
Solution Approach 2:
The patent creates composite structures by combining LiCoPO4 with other materials such as carbon coatings, conductive additives, or layered oxide structures to enhance both the energy storage capability and the structural stability during cycling, thereby reducing capacity fade while maintaining high energy density
2Use of energy by moving object
If higher voltage olivines such as LiMnPO4, LiCoPO4, or LiNiPO4 are used to increase stored energy, then the energy density increases, but structural stability and cycle life deteriorate
Solution Approach 1:
The patent optimizes the voltage and composition parameters of higher voltage olivines by adjusting cation ratios (e.g., Li:Co:Mn:Ni) and oxygen content to achieve a balance between high energy density and structural stability. Specific compositional ranges are identified that maintain olivine structure integrity at high voltages while maximizing energy storage
Solution Approach 2:
The patent introduces local compositional variations such as core-shell structures or gradient compositions where the inner core maintains high voltage for energy density while the outer shell provides structural protection and stability, allowing different regions to fulfill different functions
3Speed
If initial research improvements on LiCoPO4 are implemented to increase rate of discharge, then the discharge rate improves, but capacity fade increases
Solution Approach 1:
The patent optimizes multiple parameters simultaneously including particle size distribution, surface area to volume ratio, and compositional stoichiometry to achieve high discharge rates without excessive capacity fade. Specific parameter ranges are identified that balance kinetic performance with long-term stability
Data Source
AI summary
A positive electrode material having a nominal stoichiometry Li1+y/2Co1−x−y−z−dSizFexMyM′d(PO4)1+y/2 where M is a trivalent cation selected from at least one of Cr, Ti, Al, Mn, Ni, V, Sc, La and/or Ga, M′ is a divalent cation selected from at least one of Mn, Ni, Zn, Sr, Cu, Ca and/or Mg, y is within a range of 0<y≤0.10 and x is within a range of 0≤x≤0.2. The use of double compositional modification to LiCoPO4 increases the discharge capacity from ˜100 mAh/g to about 130 mAh/g while retaining the discharge capacity retention of the singly Fe-substituted LiCoPO4. Additional compositional modification to include Si increases the cycle life and greatly improved the coulombic efficiency to between 97-100% at a C/3 cycle rate.