Si/Mnooh Composite with Superior Lithium Storage Property

High energy/power density Li-ion batteries have been pursued since the commercialization of Graphite/LiCoO₂ LiBs, among all the cathode/anode combinations, LiBs with Si anode attracts more attention due to its potential high energy density. Nowadays, silicon have triggered much efforts due to the largest theoretical capacity (Li₂₂Si₅, ~4200 mAh g^-1), and relatively lower electrochemical alloy/de-alloy reaction voltage (~0.4 V vs. Li/Li⁺). However, the repeated large volume changes during Li insertion and extraction can lead to electrode failure. The failure mechanism is believed to involve the particle pulverization, the electric contact deterioration which will finally cause the electrode disintegration and the rapid capacity fading. Recent research also prove that the solid-electrolyte interphase (SEI) degradation is another reason for the Si anode failure. A number of strategies have been implemented to suppress the volume change and enhance or maintain the electric contact between silicon and the conductive agent. Examples typically are the Si or Si/C composite with specially designed architecture, such as silicon nanowires, silicon nanorods, porous silicon and York-shell silicon/C composite, and they present the expected capacity performance and cycling stability. However, the relatively complicated multi-step synthesis and very fluffy, insufficiently compressible product powder brings the concerns on the cost and electrode fabrication. Except the material or architecture design, binder optimization or SEI additive has also been proposed to enhance the property of Si anode, and Carboxymethylcellulose (CMC) or Alginate binder and Fluoro-ethylene carbonate (FEC) additive are now been widely used in the researches on Si anode.

Though many composites have been successfully synthesized and with good property, most of them use carbon or conductive polymer as the component with the consideration of enhancing the electrical contact or buffering the volume expansion. Here we report a new Si/MnOOH composite which shows an improved Li-ion storage performance. Hydrothermally prepared g-MnOOH was ball milled with silicon to form Si/MnOOH composite. The obtained Si/MnOOH composite exhibits an initial charge capacity of 3058 mAh g^-1 with a coulombic efficiency of 78.2% at a rate of 0.1 A g^-1 between 1.5 and 0.01 V. An excellent rate capability has been obtained on the composite, which shows a capacity of 1200 mAh g^-1 at 12 A g^-1 and 700 mAh g^-1 at 20 A g^-1. In addition, the Si/MnOOH composite presents a very stable cycling with more than 1000 mAh g^-1 after 1500 cycles. The superior electro-activity toward lithium of the Si/MnOOH electrode should be attributed to the positive effect of γ-MnOOH on the alloying/de-alloying reaction between lithium and silicon. The results supplies a new strategy to enhance the electrochemical performance of Si anode, and the facile preparation offers a new way to obtain mass-producible Si anode material with perfect Li⁺ storage property.