LiCoPO4 Cathode Doping for Capacity Fade Reduction
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Solution Overview
Problem
Current LiCoPO4-based lithium-ion positive electrode materials exhibit high capacity fade, limiting their discharge capacity and cycle life, despite initial improvements in rate of discharge.
Innovation Solution
A novel Li-ion positive electrode material with a nominal stoichiometry of Li1+y/2 Co1-x-y-z-d Si z Fe x M y M' d (PO4)1+y/2, where M is a trivalent cation and M' is a divalent cation, with specific compositional ranges for y, x, z, and d, which includes Si to enhance coulombic efficiency and cycle life, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoPO4 is used as the positive electrode material to increase energy density, then the stored energy increases, but capacity fade increases significantly
Solution Approach 1:
The patent modifies the stoichiometric parameters of LiCoPO4 by introducing non-stoichiometric composition (Li1+y/2Co1-x-y-z-dSizFexM yM'd(PO4)1+y/2) and doping with multiple elements (Si, Fe, Cr, Ti, Al, Ga) to change the electronic and structural parameters, thereby reducing capacity fade while maintaining high energy density
Solution Approach 2:
The patent creates a composite material system by combining LiCoPO4 with multiple dopant elements (Si, Fe, Cr, Ti, Al, Ga) in specific ratios, forming a multi-element doped phospho-olivine structure that synergistically improves both energy density and cycle stability
2Power
If LiCoPO4 is used to achieve high voltage operation, then the discharge voltage increases, but discharge capacity retention decreases
Solution Approach 1:
The patent changes the chemical composition parameters by introducing multiple dopants in controlled amounts, which modifies the electronic structure and electrochemical properties to maintain high voltage while improving capacity retention over cycles
Solution Approach 2:
The patent introduces localized doping elements at specific sites within the LiCoPO4 structure, where Si, Fe, Cr, Ti, Al, or Ga atoms substitute for Co atoms at specific lattice positions, creating local structural modifications that enhance overall discharge capacity retention while preserving high voltage characteristics
3Duration of action of stationary object
If Fe substitution is increased to reduce capacity fade, then cycle life improves, but initial discharge capacity increases less
Solution Approach 1:
The patent employs a composite doping strategy combining Fe with other elements (Si, Cr, Ti, Al, or Ga) where each element contributes different beneficial properties, achieving both long cycle life and high initial discharge capacity through synergistic effects rather than relying on Fe substitution alone
Solution Approach 2:
The patent optimizes the concentration parameters of multiple dopants simultaneously (x for Fe, y for M, z for Si, d for M') to achieve the optimal balance between cycle life and initial discharge capacity, rather than maximizing a single dopant concentration
Data Source
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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 Fesubstituted 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.