Positive Electrode Composition to Suppress Manganese Dissolution
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Solution Overview
Problem
Lithium manganese oxide in electrochemical devices reacts with hydrofluoric acid, leading to manganese dissolution, disruption of the solid electrolyte interphase film, and safety hazards, while lithium iron phosphate can cause floating and cracking issues in the electrode plate.
Innovation Solution
Incorporating lithium iron phosphate into the positive electrode material with controlled mass percent, particle size, and specific surface area, along with lithium manganese oxide and lithium nickel cobalt manganese oxide, to form a core-shell structure or coatings that reduce reactivity and prevent manganese dissolution, ensuring even distribution and improved safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lithium manganese oxide is used as positive electrode material to reduce cost, then manufacturing cost is reduced, but manganese dissolves when reacting with hydrofluoric acid, disrupting SEI film and causing safety hazards
Solution Approach 1:
The patent uses a composite positive electrode material consisting of lithium manganese oxide and lithium iron phosphate. The lithium iron phosphate component suppresses manganese dissolution by reacting with hydrofluoric acid preferentially, while lithium manganese oxide provides cost benefits. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both cost reduction and safety improvement.
Solution Approach 2:
Lithium iron phosphate acts as an intermediary substance that mediates the harmful reaction between hydrofluoric acid and lithium manganese oxide. It preferentially reacts with hydrofluoric acid to form a protective interface layer, preventing direct contact between the acid and manganese oxide, thereby eliminating the safety hazard while maintaining the cost advantage of lithium manganese oxide.
2Reliability
If lithium iron phosphate is added to suppress manganese dissolution, then safety is improved, but lithium iron phosphate may float in slurry causing electrode plate dryness and cracking
Solution Approach 1:
The patent optimizes multiple parameters of lithium iron phosphate including particle size (D50: 1.0-3.0 μm, D10: 0.3-0.8 μm), specific surface area (5-15 m2/g), and mass percentage (5-20%). By precisely controlling these parameters, the slurry rheology and particle distribution are optimized to prevent floating during electrode fabrication, ensuring uniform electrode plate structure while maintaining the safety benefits of manganese dissolution suppression.
Solution Approach 2:
The patent creates a heterogeneous positive electrode material composition where lithium iron phosphate particles are strategically distributed within the lithium manganese oxide matrix. This local distribution ensures that lithium iron phosphate is positioned optimally to suppress manganese dissolution at critical interfaces while maintaining overall slurry stability and preventing floating through controlled heterogeneity rather than complete homogeneity.
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 controlled composition and structure of the positive electrode material effectively suppress manganese dissolution, prevent electrode plate cracking, and enhance low-temperature performance, ensuring the safety and stability of the electrochemical device.
Implementation Method 1
lithium iron phosphate...suppressing manganese dissolution through the lithium iron phosphate
Implementation Method 2
The lithium iron phosphate and the lithium nickel cobalt manganese oxide are located in a shell layer of the core-shell structure, thereby preventing manganese dissolution
Implementation Method 3
at least a part of the positive electrode material is a core-shell structure. The lithium manganese oxide is located in a core of the core-shell structure. The lithium iron phosphate and the lithium nickel cobalt manganese oxide are located in a shell layer of the core-shell structure, thereby preventing manganese dissolution
Implementation Method 4
the lithium iron phosphate forms a coating on lithium manganese oxide, thereby reducing the reactive sites between the electrolyte solution and the lithium manganese oxide, and in turn, preventing manganese dissolution
Data Source
AI summary
A positive electrode of an electrochemical device includes a positive current collector and a positive active material layer located on one surface or both surfaces of the positive current collector. The positive active material layer includes a positive electrode material. The positive electrode material includes lithium manganese oxide and lithium iron phosphate. Based on a total mass of the positive electrode material, a mass percent of the lithium iron phosphate is denoted as a, satisfying: 5 wt %≤a≤20 wt %. Dv50 of the lithium iron phosphate is 0.8 μm to 2.0 μm. Dn10 of the lithium iron phosphate is 0.2 μm to 0.5 μm. A specific surface area of the lithium iron phosphate is not less than 5 m2/g.