Lithium Ion Battery Positive Electrode High-Rate Discharge
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Solution Overview
Problem
Conventional lithium ion secondary batteries with high Ni content, such as LiNiO2, suffer from low energy density and deteriorated high-rate discharge characteristics when attempting to increase electrode density.
Innovation Solution
A lithium ion secondary battery utilizing a positive electrode with a compound represented by Lia(NixCoyAl1-x-y)O2, having an electrode density of 3.75 to 4.1 g/cm3 and a BET specific surface area of 1.3 to 3.5 m2/g, along with a lithium salt concentration of 1.1 to 1.7 mol/L in the electrolyte solution, and an aluminum-laminated film as the outer member, to enhance high-rate discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high Ni content compounds such as LiNiO2 are used to achieve high capacity, then the battery capacity is improved, but the theoretical density is lower compared to Co-containing compounds, resulting in low energy density
Solution Approach 1:
The patent modifies the compositional parameters of the layered compound by incorporating multiple transition metal elements (Ni, Co, Mn) in specific ratios defined by the formula Li1-x-yAxB1-yC1-x-yO2. This compositional parameter change allows achieving both high capacity and high theoretical density simultaneously, resolving the contradiction between capacity and energy density.
Solution Approach 2:
The patent creates a composite layered compound combining multiple transition metal oxides (NiO2, CoO2, MnO2) in a specific structural arrangement. This composite material approach leverages the high capacity of Ni-based compounds while incorporating Co and Mn to enhance theoretical density, thus achieving both high capacity and high energy density.
2Volume of stationary object
If the electrode density is increased by methods such as roll press to achieve higher electrode density, then the energy density is improved, but the high-rate discharge characteristics deteriorate
Solution Approach 1:
The patent optimizes the pore volume parameter to a specific range (0.003 cm³/g to 0.02 cm³/g) and controls the BET specific surface area within 0.5 to 5.0 m²/g. These parameter changes allow achieving high electrode density while maintaining sufficient porosity for ion transport, thus preserving high-rate discharge characteristics.
Solution Approach 2:
The patent creates a heterogeneous structure with different regions having different properties: dense regions for high capacity and controlled porous regions for ion transport. The local porosity distribution is optimized to ensure adequate ion access to active material particles while maintaining overall high electrode density.
Data Source
AI summary
[Problem] To provide a lithium ion secondary battery having excellent high-rate discharge characteristics. [Solution] Excellent high-rate discharge characteristics are obtained by a lithium ion secondary battery in which a compound represented by Lia(NixCoyAl1-x-y)O2 (where 0.95≦a≦1.05, 0.5≦x≦0.9, 0.05≦y≦0.2, and 0.7≦x+y≦1.0) is used as a positive electrode active material in a positive electrode, the positive electrode has an electrode density of 3.75 to 4.1 g/cm3, and the positive electrode has a BET specific surface area of 1.3 to 3.5 m2/g as an electrode.