Composite Cathode Material for Stable High-Capacity Lithium Batteries
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Solution Overview
Problem
Existing lithium secondary batteries face issues with structural collapse due to excess lithium-containing transition metal oxides, leading to voltage sagging and degradation, and lack sufficient thermal stability and cycle characteristics.
Innovation Solution
A positive electrode material comprising a mixture of large and small lithium composite transition metal oxide particles, where the large particles have a lithium-to-metal ratio of 1 to 1.5 or less and an average size of 7 to 20 µm, and the small particles have a lithium-to-metal ratio of 0.9 to 1 and a crystallite size of 180 nm or more, enhancing structural stability and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If excess lithium-containing lithium transition metal oxide is used as positive electrode active material to achieve high capacity and high output, then capacity and output characteristics are improved, but irreversible capacity increases, oxygen is released, active material structure collapses, voltage sagging occurs, and battery cell degeneration is promoted
Solution Approach 1:
The patent uses a composite material system consisting of excess lithium-containing lithium transition metal oxide particles (providing high capacity) combined with lithium transition metal oxide particles having specific crystal structures (providing structural stability). This composite approach allows the system to achieve both high capacity/output characteristics and improved structural stability during charge-discharge cycles, resolving the contradiction between productivity and reliability.
2Quantity of substance
If excess lithium-containing lithium transition metal oxide is used to achieve high voltage activation, then capacity is improved, but oxygen is released to the outside of active material structure, causing structure collapse and voltage sagging
Solution Approach 1:
The patent converts the harmful effect of oxygen release into a beneficial outcome by using lithium transition metal oxide particles with specific crystal structures that can accommodate and stabilize the excess lithium without releasing oxygen. The specific crystal structure acts as a protective framework that prevents the harmful oxygen release while maintaining the high lithium content necessary for high capacity.
3Reliability
If conventional positive electrode materials are used, then structural stability is maintained, but output and capacity characteristics are insufficient
Solution Approach 1:
The patent changes key parameters of the positive electrode active material, specifically the lithium-to-transition metal ratio (exceeding 1:1) and the crystal structure characteristics (specific d-spacing values). These parameter changes enable the material to achieve both improved output and capacity characteristics while maintaining structural stability through the specific crystal structure configuration.
Data Source
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AI summary
A positive electrode material for a lithium secondary battery according to the present invention includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material and the second positive electrode active material are lithium composite transition metal oxides containing transition metals such as nickel (Ni), cobalt (Co) and manganese (Mn), the first positive electrode active material has a larger average particle size (D50) than the second positive electrode active material, a ratio (Li/Me)i of the mole number of lithium with respect to the total mole number of transition metals of the first positive electrode active material is more than 1 to 1.5 or less, a ratio (Li/Me)2 of the mole number of lithium (Li) with respect to the total mole number of transition metals of the second positive electrode active material is 0.9 to 1, and the second positive electrode active material has a crystallite size of 180 nm or more.