Silicon Negative Electrode Tapering and Oozing Portions for Battery Integrity
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Solution Overview
Problem
Lithium secondary batteries with silicon or silicon alloy negative electrodes face breakage due to volume expansion and contraction during charging and discharging, which degrades the electrode's current-collection capability and charge-discharge cycle characteristics in wound-type configurations.
Innovation Solution
A lithium secondary battery design featuring a negative electrode with a tapering portion and an oozing portion containing a high mass percentage of binder at its outer end, which enhances adhesion to the current collector and reduces breakage, along with a production method involving a gravure process for applying the negative electrode mixture slurry to form the tapering and oozing portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a mixture layer containing silicon active material and binder is disposed through sintering to tightly bond the active material to the current collector, then adhesion is improved, but the electrode breaks during charging and discharging due to volume expansion and contraction
Solution Approach 1:
The negative electrode is divided into two distinct regions: a sintered region where the active material mixture layer is tightly bonded to the current collector through sintering, and a non-sintered region at the outer end portion where the mixture layer is not sintered. This segmentation allows different portions of the electrode to serve different functions - the sintered region provides strong adhesion while the non-sintered region accommodates volume changes during charging and discharging, preventing electrode breakage
Solution Approach 2:
Different regions of the negative electrode are given different properties: the inner portion has sintered active material mixture layer for strong adhesion to current collector, while the outer end portion has non-sintered mixture layer with higher flexibility to accommodate volume expansion and contraction. This local differentiation of properties allows the electrode to simultaneously achieve both strong bonding and resistance to breakage during cycling
2Quantity of substance
If the whole electrode is configured as a wound-type battery with spiral winding, then energy density is improved, but the electrode cannot withstand expansion and breaks
Solution Approach 1:
The wound-type electrode structure is segmented into regions with different functional characteristics. The inner portions maintain tight sintering for structural stability during winding, while the outer end portions remain non-sintered to provide flexibility for volume changes. This allows the wound-type configuration to achieve high energy density while preventing electrode breakage during charging and discharging cycles
Solution Approach 2:
In the wound-type battery configuration, different radial positions of the electrode are given different properties: the inner regions (closer to the winding center) have sintered mixture layers for structural integrity, while the outer regions (at the winding periphery) have non-sintered mixture layers that can accommodate expansion. This local quality differentiation enables the electrode to withstand the mechanical stresses of wound-type construction while maintaining functionality during cycling
3Stability of the object's composition
If the inner end portion of electrode is formed as tapering shape, then separation of porous layer is suppressed, but the electrode still breaks during charging and discharging
Solution Approach 1:
The electrode structure combines a tapering shape at the inner end portion (which suppresses layer separation) with a non-sintered region at the outer end portion (which accommodates volume changes). This segmentation allows the electrode to simultaneously achieve stable layer bonding through the tapering geometry while preventing breakage through the flexible non-sintered region that expands and contracts during cycling
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 design effectively suppresses electrode breakage and enhances adhesion, leading to improved charge-discharge cycle characteristics and increased durability of the battery.
Implementation Method 1
a production method involving a gravure process for applying the negative electrode mixture slurry to form the tapering and oozing portions
Implementation Method 2
an oozing portion mainly containing the binder is formed at a tip of the tapering portion of the negative electrode mixture layer
Implementation Method 3
such an active material that alloys with lithium undergoes volume expansion and contraction during occlusion and release of lithium
Data Source
AI summary
A lithium secondary battery and a method for producing the lithium secondary battery. The lithium secondary battery includes a negative electrode 1 in which negative electrode mixture layers 2 and 3 that contain active material particles containing silicon and/or a silicon alloy and a binder are disposed on the surfaces of a current collector 4. A electrode body is formed by spirally winding, from inside to outside, a laminate body; and in an outer end portion of the negative electrode 1, the negative electrode mixture layers 2 and 3 have tapering portions 2a and 3a whose thicknesses decrease toward ends 2b and 3b of the negative electrode mixture layers 2 and 3; and oozing portions 2d and 3d mainly containing the binder are formed at the tips of the tapering portions 2a and 3a of the negative electrode mixture layers 2 and 3.