Positive Electrode Material Gradients for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in improving charge and discharge rate characteristics, discharge capacity, cycle performance, reliability, and safety, particularly in positive electrode active materials.
Innovation Solution
A positive electrode active material comprising nickel, manganese, and cobalt with specific distribution of additive elements such as magnesium, aluminum, and titanium, featuring distinct surface and inner portions with varying concentrations and crystal structures, enhances stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nickel content in the positive electrode active material is increased to improve discharge capacity, then the discharge capacity is improved, but the safety and stability deteriorate
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of additive elements (magnesium, aluminum, calcium, titanium, or zirconium) within the positive electrode active material. The additive element concentration is specifically controlled to be higher in the surface portion (within 10 nm from the surface) compared to the inner portion. This localized distribution allows the surface to provide enhanced stability and safety while the inner portion maintains high nickel content for discharge capacity, thus resolving the contradiction between capacity and safety.
2Power
If the charge and discharge rate is increased to improve power output, then the power output is improved, but the cycle performance deteriorates
Solution Approach 1:
The patent implements local quality by concentrating additive elements in the surface portion of the positive electrode active material. This surface enrichment creates a protective layer that stabilizes the material structure during high-rate charging and discharging operations, preventing degradation that would otherwise occur at elevated rates. Consequently, the material can sustain high power output while maintaining improved cycle performance.
3Reliability
If the additive element concentration is increased throughout the entire material to improve safety, then the safety is improved, but the discharge capacity deteriorates
Solution Approach 1:
The patent resolves this contradiction by applying additive elements locally rather than uniformly throughout the material. The concentration of additive elements is specifically elevated in the surface portion (within 10 nm from the surface) while the inner portion maintains lower additive element concentration, preserving the high nickel content necessary for discharge capacity. This localized approach ensures safety improvements without sacrificing overall capacity.
Solution Approach 2:
The patent applies segmentation by dividing the positive electrode active material into distinct regions: a surface portion (within 10 nm from the surface) with high additive element concentration for safety, and an inner portion with lower additive element concentration for capacity. This spatial segmentation allows each region to optimize its function, resolving the contradiction between safety and discharge capacity.
Data Source
AI summary
A positive electrode active material with excellent charge and discharge rate characteristics and a secondary battery using the positive electrode active material are provided. The positive electrode active material in which a crystallite size calculated using an XRD pattern is greater than or equal to 150 nm; the ratio of nickel to the total number of transition metal atoms is higher in an inner portion than in a first surface portion and a second surface portion; the ratio of the number of atoms of at least one element selected from cobalt and manganese to the total number of transition metal atoms is higher in the second surface portion than in the inner portion; and the concentration of at least one of additive elements is higher in the first surface portion than in the inner portion and the second surface portion is provided.