Lithium-Ion Positive Electrode Layered Structure for Cycling Stability
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Solution Overview
Problem
Lithium secondary cells face challenges with the lifespan of active materials, particularly with lithium-containing manganese oxides like LiMn2O4, which have reduced capacity and short lifespan due to significant dissolution in the electrolyte, and lithium iron phosphates like LiFePO4 and LiMnPO4, which exhibit low electron conductivity and poor durability during cycling.
Innovation Solution
A positive electrode structure comprising a current collector with a stack of layers, including a first layer with a mixture of compounds like LixMn1-y-zM′yM″zPO4, LixM2-x-y-z-wM′yM″zM′″wO2, and LixMn2-y-zM′yM″zO4, and an outer layer comprising at least 90% LixFe1-yMyPO4, which enhances cycling stability and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lithium-containing manganese oxide (LiMn2O4) is used as cathode active material, then cost is reduced and toxicity is eliminated, but capacity is reduced and lifespan is shortened due to significant dissolution in electrolyte
Solution Approach 1:
The patent uses a composite material system consisting of a spinel layer (LiMn2O4) and a phosphate layer (LiMnPO4 or LiFePO4) in a layered structure. The spinel layer provides cost-effectiveness and non-toxicity, while the phosphate layer provides structural stability and prevents dissolution, thereby extending lifespan without sacrificing the cost and toxicity advantages
2Ease of manufacture
If lithium iron phosphate (LiFePO4) or lithium manganese phosphate (LiMnPO4) is used as cathode active material, then cost is reduced and thermal stability is improved, but electron conductivity is low and durability in cycling is poor
Solution Approach 1:
The patent creates a composite structure where phosphate particles (LiFePO4 or LiMnPO4) are surrounded by a spinel shell (LiMn2O4). The phosphate core provides cost reduction and thermal stability, while the spinel shell acts as a protective barrier that prevents particle cracking and maintains structural integrity during cycling, thereby improving durability
Solution Approach 2:
The patent applies different materials with different properties to different regions: the inner core uses phosphate for thermal stability and cost, while the outer shell uses spinel for mechanical strength and cycling durability. This local differentiation of material properties allows each region to contribute its optimal characteristics to the overall performance
3Power
If high proportion of electron conductive material is added to improve discharge performance at high current, then electron conductivity is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses the spinel material (LiMn2O4) which inherently possesses good electron conductivity as the outer shell of the composite structure. This eliminates the need to add separate electron conductive additives, as the spinel shell itself provides the necessary conductivity for high current discharge performance while maintaining a relatively simple electrode structure
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 proposed electrode structure significantly improves the cycling lifespan of lithium secondary cells by combining the benefits of different active materials, offering high capacity, thermal stability, and increased user safety while maintaining lower costs.
Implementation Method 1
lithium iron phosphates like LiFePO4 and LiMnPO4, which exhibit low electron conductivity
Implementation Method 2
significant dissolution of the oxide in the electrolyte of the secondary cell
Implementation Method 3
an active material is a material which participates in the electrochemical reactions to produce electrical energy when the secondary cell discharges
Data Source
AI summary
A lithium accumulator including: a current collector; a stack of at least two layers arranged on at least one surface of the current collector, wherein a first layer is in contact with the surface of the current collector and includes a mixture of at least two compounds selected from a lithiated manganese phosphate, a lithiated transition metal oxide, and a lithiated spinel-type manganese oxide; and an outer layer including an active material having at least 90% of a lithiated iron phosphate.