Silicon
(Si) is a promising anode material for lithium-ion batteries
but has long been suffering from low conductivity, drastic volume
change, poor cycling performance, etc. Adding SiO, Al, etc. to form
Si-based binary composite films can improve some properties but have
to give up others. Here, we prepared a ternary Si–SiO–Al
composite film anode by adding SiO and Al together into Si using magnetron
sputtering. This film has an extraordinary combination of conductivity,
specific capacity, cycling stability, rate performance, etc., when
compared with its binary and unary counterparts. While both SiO and
Al can separately mitigate anode cracking resulting from the huge
volume expansion during the lithiation/delithiation cycling process,
the synergetic effect of adding SiO and Al together to form a ternary
composite film can produce much better results. This film maintains
an island structure that can efficiently buffer the volume expansion
during the cycling process, giving rise to superior cycling performance
and excellent rate performance. In addition, the cosputtered Al improves
the electrical conductivity of the anode at the same time. This unique
combination of anode properties, together with the low cost, suggests
that the Si–SiO–Al composite film has the potential
to be commercialized as a binder-free anode for lithium-ion batteries.
This work also provides an efficient means to modulate the anode properties
with more degrees of freedom.
Nickel-rich layered cathode LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is the most promising cathode material due to its high specific capacity and lower cost than lithium cobalt oxides. However, NCM811 suffers from structural instability and capacity degradation during charge−discharge cycles. Herein, we report a strategy to construct a conductive network by employing a holistic Ge coating, which interconnects Mg-doped NCM811 particles. Dopant Mg ions, serving as a "pillar" in the Li slab of NCM811, substantially enhance the structural reversibility. The Ge particles are not only coated on the electrode surface but also enter into the electrode pores to form a multidimensional conductive structure, which improves the conductivity of the electrode and slows down the interface side reaction, thus minimizing the irreversible loss of NCM811 upon long cycling. The modified NCM811 electrode delivers a high discharge capacity (∼204 mAh g −1 at 0.1C), excellent rate performance (∼155 mAh g −1 at 10C), and high capacity retention (83% after 200 cycles) even at 4.4 V. Additionally, a cylindrical full battery with graphite/modified NCM811 undergoes 1000 cycles with 86% capacity retention at 2C.
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