Efficient way to improve energy density of lithium ion batteries

著者：Iflowpower – Mofani oa Seteishene sa Motlakase se nkehang

As the active substance, the volume change reaches 270% in the charge / discharge cycle, the volume change reaches 270%, the cycle life is poor. This Body Finding Conference leads to: (1) The damage of silicon particles, and the coating from the copper concentration fluid; (2) Solid electrolyte (SEI) film is unstable in the circulatory process, the body bulk obstacles SEI sanction and repeating Composition, resulting in failure of lithium ion battery. The compaction process will make the solid phase contact more tightly, and the electronic transmission function of the progressive plate.

However, the porosity is too low, and the lithium ion transmission resistance is added, and the electrode / electrolyte interface charge transfer impedance, the magnification function is deteriorated. Generally, the graphite electrode porosity optimization is controlled at 20% -40%, while the silicon-based electrode, the compaction function is deteriorated, and the general porosity of these poles is 60% -70%, and the high porosity can harmonic material. Large, buffer particles dramatically deformed, slowing powder and falling.

However, the high porosity silicon base negative electrode sheet limits the volumetric energy density. So how do lithium-ion battery silicon base negative electrode slides? Karkarz et al. Plays the preparation process of silicon electrodes.

First, they use two mixing methods to prepare 80% by weight of silicon, 12 wt% graphene and 8 wt% CMC electrode slurry: (1) SM: convention ball milling process; (2) RAM: two-step ultrasound craft process In the first step in the pH3 buffer solution (0.17M citric acid + 0.07mkoh) Ultrasound 涣 涣 硅 and CMC, the second step in adding graphene sheets and water sustained ultrasound.

As shown in Figures 1A and D, there is a stone-ink, and the ultrasonic scattered RAM adheres to the original deposition of the graphene sheet, and the sheet is greater than 10μm, spread parallel with the collector, the coating porosity is higher, while SM is mixed, and the graphene sheet is broken, the graphene sheet is only a few micrometers. The uncharacted RAM polar porosity is about 72%, which is greater than 60% of the SM electrode.

There is no difference in silicon, two mixing methods. Nano-phosphous graphene has outstanding electronic conduction capabilities, RAM scattered adheres to the integrity of graphene sheet, and the battery cycle function is good. Then, they discuss the influence of the porosity, density, and electrochemical function of the compaction on the electrode.

As shown in Figure 1, after compaction, the graphite and silicon have not changed significantly, and only the coating is more dense. The pole sheet is made into a semi-battery detection electrochemical function, and from Fig. 2, it is as understood: (1) is added to the compact pressure, the electrode porosity decreases, the density is added, the volume ratio capacity is added.

(2) Uninterrupted, RAM porosity is about 72%, greater than 60% of the SM electrode. Moreover, the RAM electrode is more difficult, reaches 35% porosity, the RAM electrode requires 15T / cm2 pressure, while the SM pole is only 5t / cm2. This is because the graphene sheet is difficult, and the RAM pole adheres to the graphite-like structure, it is more difficult to compact.

(3) According to the completely lithium silicon volume, the volume is more than 193% accounting volume specific capacity. Under the compaction of 20T / cm2, the volume specific capacity is the largest, and the porosity of RAM and SM electrode is divided into 34%, 27%, and the corresponding volume specific capacity is 1300mAh / cm3, 1400mAh / cm3. Others, they also found that compacted extremely famished solutions to improve cycle functionality.

When the polar film is compacted, the binder and the living material particles may break at the frictional force between the particles, and even the binder itself bonds, thereby deteriorates the polar mechanical stability, cycle function cracking (Fig. 4A). The maturity process is 2 to 3 days in the environment of 80% of the humidity, in which the binder will be relocated, and better paveled in the surface of the living material particles, and set more more tuning from the head.

, Other, the copper foil will attack, the copper foil constitutes the Cu (OC (= O) -R) 2 chemical bonds, and the binding force is added, and the coating is dropped. Thus, ripening solves the ability to make a stability and cycle function. The microstructure change of the scattered - compaction - ripestage process is shown in Figure 4c, compaction leads to the breakage of the binder, the cycle stability is varied, while the binder relocation is attached from the head to the head, the electrode microstructure Change, mechanical stability advancement, corresponding circulation function progress.

If you first solve the extreme mesh, then compact, the polar circulation function is improved, but the use is not clear (Figure 4B). This is because ripening enhances the mechanical stability of the pole, but the subsequent compaction has destroyed the connection of the binder. Thus, the silicon-based electrode, in order to advance the circulation function, the bulk material is large, the polar porosity is high, but in order to advance the volumetric energy density, the compaction polar slice is lowered, the demand is to solve Improve electrode microstructure.

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