What is the problem with lithium-ion batteries using silicon crystals as a negative electrode material alone?

The battery cover is a square-shell battery cover that seals the bare cell from the outside. Each of the square-shell batteries is composed of a cover and a casing. The cover mainly includes a cover piece, a positive and negative column, and an explosion-proof valve, flip piece several parts.

The structure of silicon is different from that of graphite (see the figure below). The energy storage mechanism is similar to that of metal materials by alloying and de-alloying with lithium ions. The charge-discharge electrode reaction can be written as follows:

Si+xLi++xe-→LiXSi

As can be seen from the figure, during the charging, lithium ions are separated from the positive electrode material and intercalated between the crystal lattices inside the silicon crystal, causing a large expansion (about 300%) to form a silicon-lithium alloy. Lithium ions are separated from the crystal lattice during discharge, and a large gap is formed.

The use of a silicon crystal alone as a negative electrode material easily causes the following problems:

First, in the process of deintercalation, the volume of the silicon crystal has changed significantly. Such a volume effect easily causes the silicon anode material to be peeled off from the current collector, causing electrochemical corrosion and short circuit of the pole piece exposed foil. Affect the safety and service life of the battery.

Second, silicon carbon is the same main group element, and SEI is also coated on the silicon surface during the first charge and discharge. However, the peeling caused by the volume effect of silicon causes repeated destruction and reconstruction of SEI, thereby increasing lithium. The consumption of ions ultimately affects the capacity of the battery.

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