Lithium Transition Metal Composite Oxide for High Rate Discharge
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Solution Overview
Problem
Lithium secondary batteries using traditional LiCoO2 as a positive active material have limited discharge capacity and high rate discharge performance, which is inadequate for applications in eco-friendly vehicles requiring higher energy density and faster charging/discharging capabilities.
Innovation Solution
A lithium-transition metal composite oxide with a composition formula of Li1+αMe1-αO2, where Me includes Co, Ni, and Mn, with specific molar ratios and a crystal structure that maintains stability during charging and discharging, is used to enhance discharge capacity and high rate discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LiCoO2 is used as a positive active material, then the battery structure is simple and manufacturing is easy, but the discharge capacity is limited to only about 120 to 130 mAh/g
Solution Approach 1:
The patent uses a composite material consisting of LiCoO2 particles coated with a lithium phosphate layer. This coating structure combines the high voltage characteristics of LiCoO2 with the protective and capacity-enhancing properties of lithium phosphate, achieving a discharge capacity exceeding 140 mAh/g while maintaining manufacturing feasibility through a straightforward coating process
Solution Approach 2:
The patent modifies the surface chemistry parameters of LiCoO2 by introducing a lithium phosphate coating layer with controlled thickness and composition. This parameter change at the surface level enhances the overall discharge capacity without fundamentally altering the bulk material structure or manufacturing process
2Ease of manufacture
If LiCoO2 is used as a positive active material, then the manufacturing process is simple, but the high rate discharge performance is inadequate for eco-friendly vehicles
Solution Approach 1:
The lithium phosphate coating layer acts as a fast ion conductor that facilitates rapid lithium ion transport during high rate discharge. This composite structure maintains the simple manufacturing process of LiCoO2 while dramatically improving high rate discharge performance through the enhanced ion transport properties of the coating layer
3Quantity of substance
If the lithium phosphate coating layer is made thicker to improve discharge capacity, then the discharge capacity increases, but the manufacturing precision and coating uniformity become more difficult to control
Solution Approach 1:
The patent applies a thin but sufficient coating layer of lithium phosphate that provides the necessary capacity enhancement without requiring excessive thickness. This partial action approach achieves the required discharge capacity improvement while maintaining excellent coating uniformity and avoiding the manufacturing difficulties associated with thick coatings
Data Source
AI summary
A positive active material for a lithium secondary battery contains a lithium-transition metal composite oxide represented by a composition formula of Li1+αMe1-αO2 (Me is a transition metal element including Co, Ni, and Mn; 1.2 < (1 + α)/(1 - α) < 1.6). A molar ratio (Co/Me) of Co contained in the Me ranges from 0.24 to 0.36, and when a space group R3-m is used for a crystal structure model based on an X-ray diffraction pattern, a half width of a diffraction peak that attributes to a (003) line ranges from 0.204° to 0.303°, or a half width of a diffraction peak that attributes to a (104) line ranges from 0.278° to 0.424°.