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 face challenges in achieving high actual capacity and low internal resistance, with repeated charge/discharge cycles leading to capacity degradation and increased resistance.
Innovation Solution
A cathode material with a composition of Li2-xMIIyM(Si,MB)O4, where MII is a divalent element at the Li site, and MB compensates for electric charge differences, forming a sea-islands structure with carbon, optimizing electron transfer and structural stability.
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 (330 mAh/g), but actual capacity remains low (60-225 mAh/g) and internal resistance is high
Solution Approach 1:
The invention modifies the compositional parameters of the cathode material by introducing divalent metal elements (Mg, Cu, Zn, Mn, Fe, Co, Ni) at specific sites (Li site and/or M site) with controlled concentrations (0.03125 ≤ y ≤ 0.25). This compositional parameter change transforms the material properties to achieve both high actual capacity (240-280 mAh/g) and low internal resistance, resolving the contradiction between theoretical and actual capacity
Solution Approach 2:
The invention creates a composite cathode material structure by combining lithium iron silicate or lithium manganese silicate with divalent metal elements at specific crystallographic sites. This composite approach integrates the high theoretical capacity of the base material with the beneficial electrical conductivity and structural stability provided by the divalent metal elements, achieving both high actual capacity and low internal resistance
2Productivity
If charge/discharge cycles are repeated with high charge amount, then battery capacity is utilized effectively, but internal resistance increases and actual capacity decreases
Solution Approach 1:
The divalent metal elements are incorporated into the cathode material structure in advance to preemptively stabilize the crystal structure against degradation during charge/discharge cycling. This prior structural reinforcement cushions against the harmful effects of repeated cycling, maintaining low internal resistance and high actual capacity even after extensive cycling (500 cycles at 45°C with 90% capacity retention)
3Reliability
If carbon coating is applied to oxide grains, then electron conductivity is improved, but manufacturing complexity increases
Solution Approach 1:
The invention merges the structural modification and conductivity enhancement functions into a single step by incorporating divalent metal elements directly into the cathode material crystal structure during synthesis. This eliminates the need for separate carbon coating processes while achieving comparable or superior electron conductivity (internal resistance of 30-100 mΩ), thereby reducing manufacturing complexity
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 solution enables high actual capacity, reduced internal resistance, and improved stability against charge/discharge cycles, enhancing battery performance.
Implementation Method 1
an active material which allows lithium ion intercalation/deintercalation
Implementation Method 2
an electrically conductive auxiliary which ensures an electrical conduction path (electron conduction path) to a current collector
Implementation Method 3
The separator is placed between the cathode and the anode so as to keep electrical insulation therebetween and has pores to allow the electrolyte to pass through
Implementation Method 4
lithium salt and an organic solvent or an ionic liquid capable of dissolving the lithium salt
Data Source
AI summary
A cathode material for a lithium ion secondary battery includes an oxide represented by a composition formula Li2-xMIIyM(Si,MB)O4, wherein MII represents a divalent element; M represents at least one element selected from the group consisting of Fe, Mn, Co and Ni; and MB represents, as an optional component, an element substituted for Si to compensate for a difference between an electric charge of [Li2]2+ and an electric change of [Li2-xMIIy]n+ as needed. In the composition formula representing the oxide, x and y are −0.25<x≦0.25 and 0<y≦0.25.