Lithium Metal Oxide Cathode Coating for Stability
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Solution Overview
Problem
Current lithium batteries face challenges with stability at high temperatures and high voltages, as well as poor high-rate characteristics and cycle-life performance, particularly with over-lithiated transition metal oxides which have low electric conductivity.
Innovation Solution
A cathode active material comprising a lithium metal oxide core with an oxide coating layer, where the coating layer is formed using metal oxides or metal phosphorous oxides, enhancing electrical and thermal stability, and preventing side reactions such as transition metal elution and gas generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If over-lithiated transition metal oxide is used as cathode active material, then electric capacity is increased, but electric conductivity is reduced
Solution Approach 1:
An oxide coating layer is introduced as an intermediary substance between the over-lithiated transition metal oxide core and the electrolyte. This coating layer mediates the interaction by providing a protective interface that prevents direct contact between the low-conductivity cathode material and the electrolyte, thereby maintaining electrical conductivity while preserving the high capacity characteristics of the over-lithiated material.
Solution Approach 2:
The cathode active material is designed as a composite structure consisting of an over-lithiated transition metal oxide core (Li[LixMeyMz]O2+d where x+y+z=1 and 0<x<0.5) surrounded by an oxide coating layer. This composite structure combines the high capacity advantage of the over-lithiated core with the high conductivity and stability advantages of the oxide coating, resolving the contradiction between capacity and conductivity.
2Quantity of substance
If over-lithiated transition metal oxide is used as cathode active material, then electric capacity is increased, but cycle-life characteristics are reduced
Solution Approach 1:
The oxide coating layer is applied beforehand to the surface of the over-lithiated transition metal oxide core to provide protective cushioning. This pre-applied coating prevents direct exposure of the core material to harsh electrolyte conditions, thereby cushioning against degradation mechanisms such as transition metal elution and structural collapse that would otherwise occur during cycling, thus extending cycle life while maintaining high capacity.
Solution Approach 2:
The oxide coating layer acts as a protective intermediary that mediates the interaction between the over-lithiated transition metal oxide core and the electrolyte. By preventing direct contact, it mediates against harmful side reactions and structural degradation, thereby preserving the cycle-life characteristics of the high-capacity over-lithiated material.
3Temperature
If oxide coating layer is formed on lithium metal oxide core, then thermal stability is improved, but manufacturing complexity is increased
Solution Approach 1:
The oxide coating layer is formed on the lithium metal oxide core through preliminary action during the synthesis process. By incorporating the coating formation step into the initial material preparation (mixing precursors and calcining), the thermal stability enhancement is achieved as an integrated part of the manufacturing process rather than as a separate post-processing step, thereby minimizing the increase in manufacturing complexity.
Solution Approach 2:
The formation of the oxide coating layer is merged with the synthesis of the lithium metal oxide core. By combining these two operations into a single integrated process (simultaneous formation of core and coating during calcination), the manufacturing complexity is minimized while still achieving the desired thermal stability improvement.
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 cathode active material with an oxide coating layer improves thermal and electrical stability, leading to better high-rate capabilities and cycle-life characteristics in lithium batteries, with reduced Mo elution and gas generation at high temperatures and voltages.
Implementation Method 1
preventing side reactions such as transition metal elution and gas generation
Implementation Method 2
reduced Mo elution and gas generation at high temperatures and voltages
Data Source
AI summary
A cathode active material including: a lithium metal oxide core represented by Formula 1 below; and an oxide coating layer formed on the lithium metal oxide core:Li[LixMeyMz]O2+d. <Formula 1>In Formula 1: x+y+z=1 (0<x<0.33 and 0<z<0.1); 0≦d≦0.1; Me includes at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Mg, Zr, and B; and M includes at least one metal selected from the group consisting of Mo, W, Ir, Ni, and Mg.