Two-Layer Cathode Structure for Li-Ion Cycle and Heat Storage
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Solution Overview
Problem
Lithium-ion batteries face challenges in achieving high energy density, safety, and low costs while maintaining effective cycle and high-temperature storage performance.
Innovation Solution
The electrochemical device incorporates a positive electrode with two active material layers, where the first layer contains Mn and is thicker than the second layer, and an electrolyte with a fluorine-containing lithium salt and a low viscosity chain ester, optimized within specific concentration and thickness ratios to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 concentration in the electrolyte is reduced to improve thermal stability and reduce acidity, then high-temperature storage performance is improved, but concentration polarization increases and cycle performance deteriorates
Solution Approach 1:
The patent optimizes the LiPF6 concentration parameter within a specific range (5-12.5% by mass) to balance thermal stability and ionic conductivity. This parameter optimization resolves the contradiction by finding the optimal concentration point that provides sufficient thermal stability while maintaining adequate ionic conductivity to prevent excessive concentration polarization.
Solution Approach 2:
The electrolyte uses a composite formulation combining LiPF6 with fluorine-containing lithium salts and specific carbonate solvents. This composite approach allows the system to benefit from the high ionic conductivity of LiPF6 while the fluorine-containing salts provide enhanced thermal stability, thus resolving the contradiction between cycle performance and high-temperature storage performance.
2Productivity
If LiPF6 concentration is increased to improve ionic conductivity and cycle performance, then cycle performance is improved, but thermal stability decreases and acidity increases
Solution Approach 1:
The patent establishes an optimal upper limit for LiPF6 concentration (5-12.5% by mass) to maintain sufficient ionic conductivity for good cycle performance while preventing excessive thermal decomposition and acidity generation. This parameter control resolves the contradiction by identifying the maximum effective concentration before thermal stability deteriorates.
Solution Approach 2:
Fluorine-containing lithium salts act as intermediary components that enhance the thermal stability of the electrolyte system. These intermediaries allow the use of LiPF6 at optimized concentrations by providing a buffer against thermal decomposition, thus enabling good cycle performance without sacrificing thermal stability.
3Device complexity
If a single layer of positive active material is used to simplify electrode structure, then device complexity is reduced, but interface protection is insufficient and performance is compromised
Solution Approach 1:
The positive electrode is segmented into two distinct active material layers: a first layer containing Mn element for bulk capacity and a second layer for interface protection. This segmentation resolves the contradiction by providing differentiated functions in each layer - the first layer provides structural stability while the second layer offers enhanced interface protection, achieving both simplified overall structure and improved performance.
Solution Approach 2:
The second positive active material layer is specifically positioned at the interface region to provide localized protection where it is most needed. This local quality approach resolves the contradiction by concentrating protective functionality at the critical electrode-electrolyte interface while keeping the bulk electrode structure relatively simple through the first Mn-containing layer.
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
This configuration significantly improves the cycle and high-temperature storage performance of lithium-ion batteries, while reducing impedance and maintaining safety, thus addressing the challenges of energy density, safety, and cost.
Implementation Method 1
the electrolyte plays a role in transporting lithium ions between the positive and negative electrodes
Implementation Method 2
Reducing the lithium salt concentration can reduce rise in the acidity of the electrolyte, thereby alleviating damage caused by transition metal dissolution
Implementation Method 3
when the lithium salt concentration is low, concentration polarization is large, which affects transmission of lithium ions
Data Source
AI summary
An electrochemical device includes: a positive electrode, a negative electrode, an electrolyte, and a separator, where the positive electrode includes a positive current collector and a first positive active material layer and a second positive active material layer located on the positive current collector, the first positive active material layer is located between the positive current collector and the second positive active material layer, the first positive active material layer contains an element Mn and has a thickness of h1 μm, the second positive active material layer has a thickness of h2 μm, and h1>h2.