Positive Electrode Active Material With Li-Replenishing Surface Layer
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries face a significant increase in resistance after initial charge and discharge due to the reaction of highly active LiNiO2 with the electrolyte, leading to capacity retention issues.
Innovation Solution
A positive electrode active material comprising a first lithium transition metal composite oxide with a surface modification layer and a second lithium transition metal composite oxide, where the second oxide serves as a Li replenishing agent, is used to retard the increase in resistance by protecting the second oxide from the electrolyte.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Li2NiO2 is used as a Li replenishing agent in the positive electrode, then sufficient Li ions are supplied to the negative electrode during initial charging, but LiNiO2 reacts with the electrolyte and increases resistance after repeated charge and discharge
Solution Approach 1:
A surface modification layer comprising at least one element selected from Sr, Ca, Nb, Si, and Al is formed on the Li2NiO2 particles. This intermediary layer acts as a protective barrier between the highly active LiNiO2 and the electrolyte, preventing harmful reactions while allowing Li ion transport, thus resolving the contradiction between Li ion supply and resistance increase
Solution Approach 2:
The positive electrode active material is designed as a composite system combining Li2NiO2 particles with a surface modification layer containing specific elements (Sr, Ca, Nb, Si, or Al). This composite structure maintains the high Li ion supply capability of Li2NiO2 while the surface layer provides chemical stability and prevents electrolyte decomposition, thereby reducing resistance increase during cycling
Data Source
AI summary
A positive electrode active material according to the present invention contains first and second lithium-transition metal complex oxides at respective predetermined proportions. The first lithium-transition metal complex oxide includes a core containing at least Li, Ni, and M1 (M1 is at least one element selected from the group consisting of Mn, W, Mg, Mo, Nb, Ti, Si, and Al), and a surface modification layer that is present at least on the surface of the core. The surface modification layer includes M2 (M2 is at least one element selected from the group consisting of Sr, Ca, W, Mg, Nb, and Al). The second lithium-transition metal complex oxide includes at least a compound represented by general formula LiaNibM31-bO2 (in the formula. 1.5≤a≤2.5 and 0.95≤b≤1 are satisfied, and M3 is at least one element selected from the group consisting of Cu, Sr, Ca, Nb, Si, and Al).