Pouch Cell Electrode Composition for Wide-Temperature Safety
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Solution Overview
Problem
Existing lithium-ion pouch cells lack the ability to operate within a wide temperature range and ensure high safety, particularly in conditions of high and low temperatures, due to insufficient performance of negative and positive electrode materials and diaphragms.
Innovation Solution
Employing a silicon carbon-mesophase carbon microsphere composite as the negative electrode, a ternary positive electrode coated with lithium manganese iron phosphate, and a polyimide nanofiber separator to enhance safety and temperature range, along with a specific preparation method involving sodium carboxymethyl cellulose and polyvinylidene fluoride binders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional electrode materials are used, then the cell structure is simple, but the cell cannot maintain stable performance across a wide temperature range and safety is compromised
Solution Approach 1:
The patent employs composite electrode materials: the positive electrode uses a composite of lithium nickel cobalt manganese oxide (LNMC) and lithium iron phosphate (LFP), while the negative electrode uses silicon-carbon composite material. These composite structures enable the cell to achieve both wide temperature range operation and high safety performance without excessive structural complexity.
Solution Approach 2:
The patent modifies the chemical composition parameters of the electrode materials to achieve wide temperature range and high safety. Specifically, it adjusts the ratios of metal elements in the LNMC composite and incorporates silicon particles in the carbon matrix, thereby changing the material properties to withstand extreme temperatures while maintaining electrochemical performance.
2Quantity of substance
If high capacity negative electrode materials are used, then the energy density improves, but the cycle stability and safety deteriorate
Solution Approach 1:
The patent applies local quality by creating a heterogeneous negative electrode structure where silicon particles (high capacity) are dispersed within a carbon matrix (high stability). This local distribution allows high-capacity regions to coexist with stable regions, achieving both high capacity and excellent cycle stability. The carbon matrix provides structural integrity while silicon provides high capacity.
Solution Approach 2:
The silicon-carbon composite material utilizes a porous or heterogeneous structure where silicon particles are embedded in the carbon matrix. This structure allows the carbon to accommodate volume expansion of silicon during cycling, thereby maintaining structural stability and safety while enabling high capacity from the silicon component.
3Productivity
If conventional diaphragm materials are used, then the manufacturing cost is low, but the charge-discharge rate and high temperature safety are insufficient
Solution Approach 1:
The patent changes the material parameter of the diaphragm from conventional polyolefin to polyimide (PI) nanofiber membrane. This material substitution enables the diaphragm to withstand temperatures above 250°C and improves charge-discharge rate through its nanofiber structure, which provides higher porosity and ion transport efficiency.
Solution Approach 2:
The polyimide nanofiber diaphragm utilizes a nanofiber porous structure that provides high porosity and interconnected pore networks. This structure facilitates rapid ion transport, improving charge-discharge rate, while the nanofiber morphology enhances thermal stability and prevents thermal runaway at high temperatures.
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 combination of these materials improves the cell's capacity, cycle life, and safety by preventing thermal runaway and maintaining electrical performance across a wide temperature range, including high and low temperatures.
Implementation Method 1
The PI diaphragm may withstand high temperatures above 250° C. When piercing the diaphragm, the local overheating caused by the micro-short circuit or small area short circuit of the cell will not melt the PI diaphragm
Implementation Method 2
During the cycle, the mesophase carbon microspheres may alleviate the volume expansion of the silicon negative electrode
Implementation Method 3
The hard carbon coating layer may reduce the side reaction between the silicon negative electrode and the electrolyte and form a stable solid electrolyte interface layer
Data Source
AI summary
The pouch cell includes a positive electrode, a negative electrode, and a diaphragm placed between the positive electrode and the negative electrode. The positive electrode material includes a ternary material coated with lithium manganese iron phosphate; the negative electrode material includes a silicon carbon-mesophase carbon microsphere composite material; the diaphragm is a polyimide nanofiber diaphragm. The present disclosure uses silicon carbon-mesophase carbon microsphere composite material as the negative electrode, lithium manganese iron phosphate coated ternary positive electrode as the positive electrode material, and polyimide nanofiber separator. The safety is obviously improved during piercing. Meanwhile, it may take into account the electrical performance, improve the capacity, charge and discharge rate, long cycle performance and wide temperature range performance of lithium-ion cells; it also improves the service life and cycle life; it has low calorific value, good safety, high stability, and is not prone to dangerous situations such as combustion or explosion.