Coated Cathode Active Material for Stable Solid-State Battery Interfaces
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Solution Overview
Problem
The formation of a high-resistance layer at the interface between sulfide-based solid electrolytes and oxide positive electrode active materials in all-solid-state lithium ion secondary batteries leads to a decrease in battery capacity during repeated charging and discharging, which existing coatings like lithium niobate and phosphoric acid compounds fail to adequately prevent.
Innovation Solution
A coated positive electrode active material is developed with a lithium metal complex oxide having a layered rock salt-type structure and a coating layer containing lithium, phosphorus, and a pentavalent transition metal element, such as niobium, applied at a coating ratio of 60% or greater to inhibit interfacial reactions and maintain battery capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a sulfide-based solid electrolyte is used in all-solid-state lithium ion secondary batteries, then high lithium ion conductivity is achieved, but a high-resistance layer forms at the interface with oxide positive electrode active materials during charging and discharging
Solution Approach 1:
A coating layer comprising lithium phosphate and lithium niobate is applied to the surface of the positive electrode active material particles. This coating layer acts as an intermediary between the sulfide-based solid electrolyte and the oxide positive electrode active material, preventing direct contact and the formation of high-resistance layers, thereby maintaining battery capacity stability while preserving high lithium ion conductivity.
2Reliability
If lithium niobate coating is applied to prevent high-resistance layer formation, then interface stability is improved, but the coating decomposes under charging at voltage of 4.6 V
Solution Approach 1:
The coating layer is designed as a composite material comprising both lithium phosphate and lithium niobate. This composite structure combines the protective properties of lithium niobate with the electrochemical stability of lithium phosphate, enabling the coating to withstand charging voltages of 4.6 V without decomposition while maintaining interface stability.
3Stability of the object's composition
If phosphoric acid compounds are used to inhibit mixing between positive electrode active material and coating layer, then mixing prevention is achieved, but the compounds damage the positive electrode active material surface in acidic solution or lose phosphorus in organic solution
Solution Approach 1:
The coating layer composition is optimized by controlling the molar ratio of lithium phosphate to lithium niobate within 9:1 to 1:9. This parameter adjustment creates a balanced coating that provides mixing prevention functionality while minimizing surface damage and phosphorus loss, as the specific compositional ratio optimizes chemical stability and reduces harmful reactions.
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 coated positive electrode active material effectively inhibits the decrease in battery capacity by preventing interfacial resistance and mixing, ensuring stable performance during repeated charging and discharging cycles.
Implementation Method 1
a coating layer which coats at least a part of a surface of the lithium metal complex oxide... the coating layer contains lithium, phosphorus, and an element Z, where the element Z is at least one or more types of pentavalent transition metal elements
Implementation Method 2
sulfide-based solid electrolytes have a high lithium ion conductivity and are favorable for use in all-solid-state lithium ion secondary batteries
Data Source
Figure 1~2
Figure 3
AI summary
A coated positive electrode active material for lithium ion secondary batteries, including: a lithium metal complex oxide; and a coating layer coating at least a part of a surface of the lithium metal complex oxide at a coating ratio of 60% or greater, wherein the lithium metal complex oxide has a layered rock salt-type structure and contains lithium (Li), nickel (Ni), and an element M (M) at a ratio by number of moles of Li:Ni:M=a:1-x:x, where "a" and "x" satisfy relationships of 0.98≤a≤1.20 and 0≤x≤1.0, and the element M is one or more types of elements except lithium, nickel, and oxygen, and wherein the coating layer contains lithium, phosphorus, and an element Z, and the element Z is at least one or more types of pentavalent transition metal elements.