Mixed Cathode Material for Stable Power in Low SOC Lithium Batteries
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Solution Overview
Problem
Lithium secondary batteries used in series-type plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) face limitations in maintaining stable power across a wide state of charge (SOC) range, particularly in low SOC ranges, due to rapid power decreases caused by increased resistance in manganese-rich cathode materials, which restricts their application in vehicles dependent solely on battery power.
Innovation Solution
A mixed cathode active material combining lithium manganese oxide (Mn-rich) with a second cathode active material having a lower operating voltage, such as Li4Mn5O12, is developed to complement power decreases in low SOC ranges, ensuring stable power delivery across the entire SOC range by incorporating conductive materials like graphite and conductive carbon to enhance electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium manganese oxide (Mn-rich) is used as cathode active material to achieve high capacity, then energy density is improved, but power rapidly decreases in low SOC range due to increased resistance
Solution Approach 1:
The patent combines lithium manganese oxide (Mn-rich) with a second cathode active material having a lower operating voltage to create a composite cathode material. This composite structure allows the Mn-rich component to provide high capacity while the second material compensates for power loss in low SOC range, resolving the contradiction between energy density and power maintenance.
Solution Approach 2:
The patent modifies the operating voltage parameter by introducing a second cathode active material with lower operating voltage. This parameter change enables the cathode to maintain stable power delivery across the entire SOC range, particularly improving performance in the low SOC range where the original Mn-rich material failed.
2Quantity of substance
If lithium manganese oxide (Mn-rich) is used to achieve high capacity, then energy density is improved, but available SOC range becomes narrow due to power decrease
Solution Approach 1:
By creating a composite cathode material combining Mn-rich lithium manganese oxide with a lower voltage second cathode material, the patent expands the available SOC range. The second material becomes active in low SOC conditions, effectively widening the usable charge range while preserving the high energy density benefits of the Mn-rich component.
3Quantity of substance
If LiCoO2 is used to achieve high energy density, then capacity is improved, but safety deteriorates due to structural instability and oxygen discharge
Solution Approach 1:
The patent replaces LiCoO2 with a composite cathode material based on lithium manganese oxide combined with a second stable cathode material. This composite approach maintains high energy density while the manganese oxide structure provides improved thermal and structural stability, eliminating the safety issues associated with oxygen discharge from LiCoO2.
Solution Approach 2:
The patent substitutes the expensive and safety-prone LiCoO2 material with lithium manganese oxide-based composite materials that offer comparable energy density but superior safety characteristics, effectively replacing a high-risk material with a safer alternative.
Data Source
AI summary
The present invention relates to a mixed positive electrode active material and to a lithium secondary battery comprising the same, wherein the mixed positive electrode active material comprises lithium manganese oxide expressed by the following chemical formula 1 and Li4Mn5O12 having a stoicheiometric spinel structure with a flat level voltage profile in the range of 2.5 V to 3.3V. [chemical formula 1] xLi2MnO3 · (1-x)LiMO2, wherein 0<x<1, and M is one element selected from a group consisting of Al, Mg, Mn, Ni, Co, Cr, V and Fe, or two or more elements selected from the group and applied at the same time. The mixed positive electrode active material and the lithium secondary battery comprising the same have enhanced stability, and in which said Li4Mn5O12 supplements a low output in a low SOC range to maintain an output at the level higher than a required output level, thereby widening an available SOC range. The mixed positive electrode active material and the lithium secondary battery comprising the same may be suitably used in PHEV, EV or the like.