Lithium Secondary Battery with Amorphous Carbon Anode
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Solution Overview
Problem
Lithium secondary batteries used in hybrid electric vehicles face challenges with high output requirements, poor cycle characteristics, and stability issues due to limitations in cathode and anode materials, as well as electrolyte decomposition problems with existing materials.
Innovation Solution
A lithium secondary battery design utilizing lithium metal phosphate as the cathode active material, amorphous carbon as the anode active material, and an electrolyte comprising a lithium salt and an ether-based solvent with propylene carbonate, which improves output characteristics and stability by reducing internal resistance and preventing electrolyte decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiCoO2 is used as cathode active material, then energy density is improved, but output characteristics deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the cathode material by doping transition metals (Mn, Ni, Co, Cu, Zn, Al, Ga, In, or B) into the LiFePO4 structure. This modifies the electronic and ionic conductivity parameters of the material, enabling it to achieve both high energy density and superior output characteristics required for HEV applications.
Solution Approach 2:
The patent creates a composite cathode material by combining LiFePO4 with transition metal dopants. This composite structure integrates the high voltage platform of LiFePO4 with enhanced conductivity from transition metals, resolving the contradiction between energy density and output characteristics.
2Stability of the object's composition
If LiFePO4 is used as cathode active material, then stability is improved, but electron conductivity deteriorates
Solution Approach 1:
The patent modifies the electron conductivity parameter of LiFePO4 by controlling doping concentration (0.01≤x≤0.5 in Li1-xMxFe1-yM''y(PO4)Oz) and material synthesis conditions. This enables the material to maintain structural stability while achieving sufficient electron conductivity for practical battery applications.
Solution Approach 2:
The patent applies local doping strategy where transition metals are introduced at specific sites in the LiFePO4 crystal structure. This creates local regions with enhanced conductivity without compromising the overall structural stability of the olivine framework.
3Use of energy by moving object
If crystalline graphite is used as anode active material, then energy density is improved, but output characteristics deteriorate
Solution Approach 1:
The patent changes the anode material from crystalline graphite to amorphous carbon, fundamentally altering the structural parameters. Amorphous carbon provides shorter Li-ion diffusion paths and better contact with electrolyte, enabling both high energy density and superior rate capability/output characteristics.
Solution Approach 2:
Instead of using the conventional crystalline graphite structure, the patent inverts to amorphous carbon structure. This inversion of the standard approach resolves the contradiction by providing both high capacity and excellent rate performance through the disordered structure's inherent short diffusion paths.
4Reliability
If ester based electrolyte is used, then ionic conductivity is improved, but decomposition occurs
Solution Approach 1:
The patent changes the electrolyte composition parameters by using cyclic carbonates (EC, PC, GVL) and chain carbonates (DMC, DEC, EMC) with specific ratios, along with lithium salts (LiPF6, LiBF4, LiCF3SO3). This optimized composition achieves high ionic conductivity while preventing decomposition through favorable electrochemical stability windows.
Solution Approach 2:
The patent creates a composite electrolyte system by combining multiple carbonate solvents with different properties. The cyclic carbonates provide high dielectric constant and stability, while chain carbonates provide low viscosity and high ionic conductivity, achieving a balance that prevents decomposition while maintaining conductivity.
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 battery exhibits superior high-temperature and low-temperature output characteristics, extended cycle life, and enhanced stability, making it suitable for hybrid electric vehicles with improved ionic conductivity and reduced internal resistance.
Implementation Method 1
an electrolyte for lithium secondary batteries including a lithium salt and an ether based solvent, wherein propylene carbonate (PC) is included in an amount of 1 wt % to 60 wt % in the electrolyte for lithium secondary batteries
Implementation Method 2
a cathode active material including a lithium metal phosphate according to Formula 1 below: Li1+aM(PO4−b)Xb
Implementation Method 3
an anode active material including amorphous carbon
Data Source
AI summary
Disclosed is a lithium secondary battery including: (i) a cathode active material including a lithium metal phosphate according to Formula 1 below; (ii) an anode active material including amorphous carbon; and (iii) an electrolyte for lithium secondary batteries including a lithium salt and an ether based solvent, wherein propylene carbonate (PC) is included in an amount of 1 wt % to 60 wt % in the electrolyte for lithium secondary batteries, based on the total weight of the electrolyte,Li1+aM(PO4−b)Xb (1)wherein M is at least one selected from metals of Groups II to XII; X is at least one selected from F, S and N, −0.5≤a≤+0.5, and 0≤b≤0.1.