Silicon Oxide Negative Electrode with Carbon Film for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using silicon dioxide with microcrystals as negative electrode material experience significant expansion and contraction during charging and discharging, leading to a sudden drop in capacity and inadequate discharge and cycle characteristics.
Innovation Solution
A negative electrode material powder with a conductive carbon film on the surface of lower-silicon-oxide powder, having a specific surface area between 0.3 m2/g and 40 m2/g, and no SiC peak at 2θ=35.6°±0.1°, with a carbon film coverage rate of 0.2% to 2.5% by mass, and specific resistance of 100000 Ωcm or less, to suppress irreversible capacity formation and enhance reversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon dioxide with microcrystals of silicon is used as negative electrode material, then charging and discharging capacities are enhanced, but significant expansion and contraction occur during occlusion and release of lithium ions, leading to deterioration of cycle characteristics
Solution Approach 1:
The patent applies local quality by creating a non-uniform carbon layer distribution on the silicon oxide surface. The carbon layer thickness varies locally, with thicker regions at particle surfaces and thinner regions internally, providing differential protection against expansion/contraction while maintaining lithium ion conductivity where needed.
Solution Approach 2:
The patent uses composite materials by combining silicon oxide particles with a carbon layer to form a composite negative electrode material. This composite structure leverages the high capacity of silicon oxide while the carbon component provides structural stability and conductivity, resolving the contradiction between capacity enhancement and cycle durability.
2Reliability
If carbon powder is mixed with silicon oxide powder as conductive auxiliary agent, then electric conductivity is secured at contact portions, but locations far from contact portions cannot function as negative electrode active material due to insufficient electric conductivity
Solution Approach 1:
The patent merges the functions of the carbon conductive auxiliary agent and the carbon protective layer by forming a continuous carbon layer on the silicon oxide surface. This unified carbon structure simultaneously provides conductivity throughout the particle surface and protection against expansion, eliminating the need for separate carbon powder mixing and ensuring all active material participates in reactions.
3Quantity of substance
If conventional negative electrode active materials are used to improve energy density, then charging and discharging capacities are enhanced, but dendrite or passivated compound generation occurs, leading to significant electrode deterioration
Solution Approach 1:
The patent introduces a carbon layer as an intermediary between the silicon oxide active material and the electrolyte. This carbon intermediary prevents direct contact between the electrolyte and silicon oxide surface, thereby suppressing dendrite formation and passivated compound generation while still allowing lithium ion transport, thus protecting the electrode from harmful effects.
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 solution results in lithium ion secondary batteries with improved first cycle efficiency and cycle characteristics, achieving a reversible capacity of 2007 mAh/g and maintaining discharge capacity over repeated charge/discharge cycles.
Implementation Method 1
having a conductive carbon film on the surface of lower-silicon-oxide powder
Implementation Method 2
capable of occluding and releasing lithium ions
Implementation Method 3
When charging and discharging are performed, lithium ions reciprocate between the positive electrode 1 and the negative electrode 2 through the electrolyte of the separator 3
Data Source
AI summary
A negative electrode material powder for a lithium ion secondary battery having a conductive carbon film on the surface of a lower-silicon-oxide powder; wherein a specific surface area in BET measurement ranges from more than 0.3 m2/g to 40 m2/g, and no SiC peak appears at 2θ=35.6°±0.01° or the half-value width of the appeared peak is 2° or more in XRD measurement using CuKα rays. The proportion of said carbon film preferably ranges from 0.2% to 2.5% by mass. Said powder preferably has 100000 Ωcm or less of specific resistance. In XRD, P2/P1<0.01 is preferably satisfied between the highest value P1 of halo of SiOx and a value P2 of the strongest linear peak of Si (111) above the halo.Accordingly, said powder can be used in the secondary battery with a large discharge capacity and a preferable cycle characteristics for practical use.