
In the early days, metal lithium was directly used as the negative
electrode material, but during the charging and discharging process, dendritic
lithium was generated, which could puncture the diaphragm and cause short
circuits, leakage, and even explosions. Using Aluminium–lithium alloys can solve
the problem of dendrite lithium, but after several cycles, there will be serious
volume expansion and even powdering. The concept of rocking chair batteries has
solved this problem by utilizing non-metallic materials with layered structures
such as graphite to store lithium to avoid the generation of dendritic lithium,
thereby greatly improving the safety of battery use [3].
Carbon materials can be divided into natural carbon materials and
artificial carbon materials. Natural graphite materials have high graphitization
degree, complete crystallization, multiple embedding positions, and large
capacity, but are sensitive to electrolytes and have poor cycling stability.
Artificial carbon materials include soft carbon materials and hard carbon
materials. There is a large irreversible capacity in hard carbon materials.
Adding potassium and boron into carbon materials and coating a layer of Ag, Zn,
Sn [4] on the surface of carbon fibers can effectively improve the capacity and
charge discharge efficiency of materials.
The addition of low melting point metals such as Bi, Pb, Sn, and Cd into
lithium to form a lithium metal alloy has high reversible capacity. However,
during the charging and discharging process, there will be volume expansion (up
to 200%), resulting in powdering and poor contact between particles and electron
transfer. The material synthesized by Dahn [5] by depositing Sn on the surface
of electrochemical inert SnFe3C grains has good cycling performance, but low
capacity.
In order to solve the problem of metal powder formation, Idota [6] proposed
using metal oxides such as SnO2 instead of pure metals as anode materials. Metal
oxide MO (M=Co, Cu, Ni, Fe, etc.) nanomaterials can still maintain a capacity of
700mAh • g-1 after 100 cycles [7]. In addition, other metal oxides such as
InVO4, FeVO4, MnV2O6, and TiO2 also have significant lithium storage capacity,
but their irreversible capacity is relatively large.
Recently, some transition metal nitrides, Li3-xMxN (M: Co, Ni, Cu), have
been discovered to have excellent electrochemical stability and high reversible
storage, with a charge discharge capacity of up to 760mAh • g-1 [8]. Li6Co0.4N
has a capacity of up to 900mAh • g-1 [9] and can be used to improve the
electrochemical performance of SnO. The study of its lithium intercalation
mechanism found that after the first lithium removal, the material will
transform from hexagonal phase to amorphous phase, and the amorphous phase can
embed a large number of lithium ions.
5-nanometer silicon nanosilicon also has high lithium storage capacity and
is currently a research hotspot. High capacity can be achieved by uniformly
dispersing nano Si in electrochemical inert TiN lattice and depositing silicon
onto porous nickel substrate to produce thin film silicon. By using chemical
vapor deposition method to composite some nano silicon into carbon materials,
the capacity of the material can be significantly increased, while the capacity
of carbon coated silicon can reach 1200mAh · g-10.
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