Positive Electrode Bilayer Pore Structure for Low-Temperature Batteries
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Solution Overview
Problem
Secondary batteries exhibit poor low-temperature performance, characterized by reduced discharge capacity and charge performance, which restricts their application in electric vehicles and extreme environments due to inadequate lithium-ion transport capacity.
Innovation Solution
A positive electrode sheet with a bilayered three-level pore size distribution in the active material layers, comprising specific primary, secondary, and tertiary pore sizes, ensures consistent lithium-ion transport capacity and avoids space-occupying and filling effects, thereby enhancing low-temperature charge-discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer active material structure is used, then the battery structure is simple and manufacturing is easier, but the low-temperature lithium-ion transport capacity is insufficient
Solution Approach 1:
The active material layer is divided into inner and outer layers with different pore size distributions. The inner layer contains larger pores (1-5 μm) for bulk lithium-ion transport, while the outer layer contains smaller pores (0.1-1 μm) for surface lithium-ion exchange, enabling each layer to specialize in different transport functions and collectively improve low-temperature performance
Solution Approach 2:
Different regions of the active material layer are赋予 different pore size characteristics tailored to their functional requirements. The inner layer near the current collector has larger pores optimized for electrolyte penetration and bulk ion transport, while the outer layer at the surface has smaller pores optimized for rapid lithium-ion insertion/extraction, creating local optimization throughout the layer
2Quantity of substance
If micropores with small pore sizes are increased to improve surface area, then energy density is improved, but lithium-ion transport capacity in low-temperature environment sharply declines
Solution Approach 1:
The pore system is segmented into two distinct size ranges distributed across inner and outer layers. Larger pores (1-5 μm) in the inner layer provide efficient lithium-ion transport channels that remain functional at low temperatures, while smaller pores (0.1-1 μm) in the outer layer provide high surface area for electrochemical reactions, achieving both high energy density and maintained transport capacity
Solution Approach 2:
The invention transitions from a single uniform pore size to a multi-dimensional pore size distribution across different layers. By adding the layer dimension, the system can simultaneously accommodate different pore sizes in different spatial locations, allowing small pores to be concentrated at the surface where they are needed for reactions, while large pores are positioned internally for transport
3Quantity of substance
If the pore size distribution is optimized for high-temperature performance, then high-temperature discharge capacity is improved, but low-temperature charge performance becomes extremely poor
Solution Approach 1:
The pore structure is optimized locally for different temperature conditions through spatial distribution. The inner layer's larger pores facilitate electrolyte access and ion transport under all temperature conditions, while the outer layer's smaller pores provide high surface area for rapid reactions at high temperatures and maintained functionality at low temperatures, creating a structure that adapts to different thermal environments
Solution Approach 2:
The active material layer is segmented into temperature-responsively functional zones. The inner layer handles bulk transport requirements that are critical across all temperatures, while the outer layer handles surface reaction requirements that benefit from small pores at high temperatures but remain functional at low temperatures due to the supportive inner layer 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 bilayered pore size distribution significantly improves the low-temperature energy retention rate and maximum output power of secondary batteries by maintaining lithium-ion transport capacity and conductivity, outperforming comparative examples with monolayer or poorly distributed pore sizes.
Implementation Method 1
guarantees lithium-ion transport capacity of micropores in the active material layer, but also achieves consistent lithium-ion transport capacity in the inner active material layer and the outer active material layer
Implementation Method 2
the pore size distribution in the inner active material layer and the outer active material layer is reasonable, thereby avoiding space occupying effects and filling effects, further avoiding or reducing sharp decline of internal lithium-ion transport capacity of the secondary battery in a low-temperature environment
Data Source
AI summary
A positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode active material layer includes an inner active material layer and an outer active material layer successively stacked. The inner active material layer has a three-level pore size distribution: an inner primary pore size distribution from 3 nm to 10 nm, an inner secondary pore size distribution from 10 nm to 100 nm, and an inner tertiary pore size distribution from 0.1 μm to 2 μm. The outer active material layer has a three-level pore size distribution: an outer primary pore size distribution from 0.5 nm to 3 nm, an outer secondary pore size distribution from 10 nm to 100 nm, and an outer tertiary pore size distribution from 0.1 μm to 2 μm.