Lithium Iron Silicate Cathode Material for High Capacity Batteries
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Solution Overview
Problem
Lithium iron silicate and lithium manganese silicate-based cathode materials for lithium ion secondary batteries exhibit high theoretical capacity but struggle with achieving actual capacities above 1.5 Li and suffer from high internal resistance, limiting energy density and thermal management.
Innovation Solution
The cathode material is optimized by modifying the composition to include excessive lithium ions (Li2+z(M,MA)(Si,MB)O4) with elements like Fe, Mn, and Ni, and incorporating a carbon material in a sea-islands structure to reduce internal resistance, where x represents the excess lithium content and MA/MB elements provide charge compensation, forming a stable sublattice.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium iron silicate or lithium manganese silicate is used as cathode material, then theoretical capacity is high, but actual capacity is limited and internal resistance is high
Solution Approach 1:
The patent modifies the stoichiometric composition of lithium iron silicate by adding excess lithium (Li2+xFeSiO4 where x=0.03125), creating a non-stoichiometric compound. This parameter change in composition enables the material to achieve actual capacity exceeding 1.5 Li while reducing internal resistance, resolving the contradiction between theoretical capacity and actual performance
Solution Approach 2:
The patent creates a composite structure where excess lithium forms a sublattice within the lithium iron silicate matrix. This composite arrangement, combined with carbon coating, improves electron conductivity and enables higher actual capacity while maintaining structural stability, thus resolving the capacity and resistance contradiction
2Reliability
If carbon coating is applied to metal oxide surface, then electron conductivity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent combines carbon coating with the lithium iron silicate synthesis process into a single integrated manufacturing step. The carbon source is incorporated during the same heat treatment process that forms the lithium iron silicate structure, eliminating separate coating steps and reducing manufacturing complexity while achieving the desired conductivity improvement
3Quantity of substance
If excessive lithium is added to lithium iron silicate, then actual capacity increases, but internal resistance may increase
Solution Approach 1:
The patent precisely controls the excess lithium content at x=0.03125, which is optimized to provide sufficient lithium for high capacity while avoiding excessive lithium that would increase resistance. This precise parameter control resolves the contradiction between capacity enhancement and resistance management
Solution Approach 2:
The excess lithium forms a structured sublattice within the lithium iron silicate, creating a composite material with optimized properties. This structured arrangement allows high lithium content for capacity while maintaining good ionic and electronic conductivity, thus resolving the capacity-resistance trade-off
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
This approach results in a cathode material with reduced internal resistance and enhanced actual capacity, enabling higher energy density and improved thermal management in lithium ion secondary batteries.
Implementation Method 1
making carbon particles, carbon fiber or the like adhere to the surface of the metal oxide
Implementation Method 2
an active material which allows lithium ion intercalation/deintercalation
Data Source
AI summary
A cathode material for a lithium ion secondary battery includes an oxide represented by a composition formula Li2+x(M,MA)(Si,MB)O4, wherein M represents at least one element selected from the group consisting of Fe, Mn, Co and Ni; MA and MB represent elements substituted for parts of M and Si, respectively, to compensate for an electric charge equivalent to x of Li+; and at least one of MA and MB is included. In the composition formula representing the oxide, 0<x≦0.25.