Positive Electrode Core-Shell Coating for Low-Temperature Rate Performance
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Solution Overview
Problem
Secondary batteries based on existing lithium manganese iron phosphate materials suffer from poor kinetic performance, low rate performance, short low-temperature cycle life, and low low-temperature cycling capacity retention due to increased internal phase change resistance and one-dimensional lithium ion channels.
Innovation Solution
A positive electrode plate with a core-shell structure active material, comprising an inner core of Li1+xMn1-yAyP1-zRzO4 coated with pyrophosphate and phosphate layers, and a carbon-containing layer, where A includes elements like Zn, Al, and R includes elements like B, Si, and S, to enhance lithium ion migration and reduce transition metal dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium manganese iron phosphate is used as positive electrode active material, then secondary batteries have good cycling stability and safety, but kinetic performance and rate performance are poor
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core maintains the original lithium manganese iron phosphate composition for stability, while the outer shell contains different lithium phosphate compositions optimized for kinetic performance. This allows different regions of the same particle to have different properties - the core provides cycling stability while the shell enhances rate performance and reduces phase change resistance.
Solution Approach 2:
The patent uses composite materials by combining lithium manganese iron phosphate with lithium phosphate compounds (such as Li3PO4, Li2SiO3, Li2SO4) to form a core-shell structured composite. This composite structure integrates the advantages of both materials: the stability of lithium manganese iron phosphate and the superior ionic conductivity of lithium phosphate, thereby improving overall kinetic performance while maintaining cycling stability.
2Reliability
If lithium manganese iron phosphate is used as positive electrode active material, then secondary batteries have good safety performance, but rate performance is low
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core maintains the original lithium manganese iron phosphate composition for stability, while the outer shell contains different lithium phosphate compositions optimized for kinetic performance. This allows different regions of the same particle to have different properties - the core provides cycling stability while the shell enhances rate performance and reduces phase change resistance.
Solution Approach 2:
The lithium phosphate shell acts as an intermediary layer between the lithium manganese iron phosphate core and the electrolyte. This intermediary shell facilitates faster lithium ion transport to and from the core material, thereby improving rate performance while the core continues to provide safety performance. The shell mediates the interaction between the active material and electrolyte, reducing harmful side reactions.
3Reliability
If lithium iron phosphate is used as positive electrode active material, then secondary batteries have excellent cycling stability, but internal phase change resistance increases during charging and discharging
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core maintains the original lithium manganese iron phosphate composition for stability, while the outer shell contains different lithium phosphate compositions optimized for kinetic performance. This allows different regions of the same particle to have different properties - the core provides cycling stability while the shell enhances rate performance and reduces phase change resistance.
Solution Approach 2:
The lithium phosphate shell acts as an intermediary layer between the lithium manganese iron phosphate core and the electrolyte. This intermediary shell facilitates faster lithium ion transport to and from the core material, thereby improving rate performance while the core continues to provide safety performance. The shell mediates the interaction between the active material and electrolyte, reducing harmful side reactions.
4Quantity of substance
If lithium manganese iron phosphate is used as positive electrode active material, then secondary batteries have good energy density, but low-temperature cycle life is short
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core maintains the original lithium manganese iron phosphate composition for stability, while the outer shell contains different lithium phosphate compositions optimized for kinetic performance. This allows different regions of the same particle to have different properties - the core provides cycling stability while the shell enhances rate performance and reduces phase change resistance.
Solution Approach 2:
The patent uses parameter changes by modifying the composition and structure of the positive electrode active material. Specifically, it changes the phase structure from a single-phase material to a core-shell structured composite material, and adjusts the ratio of different phases to optimize both energy density and low-temperature cycle life. The shell layer parameters (composition, thickness) are specifically designed to improve low-temperature ionic conductivity.
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 solution significantly improves the kinetic and rate performance, cycling stability, and low-temperature performance of secondary batteries by reducing transition metal dissolution and enhancing lithium ion conductivity, while maintaining high energy density and safety.
Implementation Method 1
the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4
Implementation Method 2
the second coating layer comprises a carbon element
Implementation Method 3
the inner core comprises Li1+xMn1-yAyP1-zRzO4, wherein A comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge
Data Source
AI summary
A positive electrode plate may comprise a positive electrode current collector and positive electrode film layers having a single-layer or multi-layer structure provided on at least one surface of the positive electrode current collector; when the positive electrode film layers have a single-layer structure, at least one of the positive electrode film layers may comprise a first positive electrode active material and a second positive electrode active material selected from LiFePO4, carbon-coated LiFePO4, LiFebDcPO4 and carbon-coated LiFebDcPO4; and/or when the positive electrode film layers have a multi-layer structure, at least one layer of the at least one of the positive electrode film layers may comprise the first and second positive electrode active materials; and the first positive electrode active material may comprise an inner core containing Li1+xMn1-yAyP1-zRzO4, a first coating layer containing pyrophosphate and phosphate, and a second coating layer containing a carbon element.