Wenqiang Tu

Insight into the capacity fading of layered lithium-rich oxides and its suppression via a film-forming electrolyte additive

The capacity fading of layered lithium-rich oxide (Li1.2Mn0.54Ni0.13Co0.13O2, LLO) cathodes greatly hinders their practical application in next generation lithium ion batteries. It has been demonstrated in this work that the slow capacity fading of a LLO/Li cell within 120 cycles is mainly caused by electrolyte oxidation and LLO phase transformation with Ni dissolution. After 120 cycles, the dissolution of Mn becomes worse than that of Ni, leading to structural destruction of the generated spinel phase structure of LLO and fast capacity fading. Tripropyl borate (TPB) is proposed as a film-forming electrolyte additive, which shows a great capability to enhance the cycling stability of LLO/Li, with a capacity retention improvement from 21% to 78% after 250 cycles at 0.5C. Electrochemical and physical characterization demonstrated that the TPB-derived SEI film shows great capability to suppress electrolyte oxidation and the structural destruction of the generated spinel phase of LLO.

Mechanism of cycling degradation and strategy to stabilize a nickel-rich cathode

A nickel-rich LiNi0.8Co0.15Al0.05O2 (NCA) cathode possesses high specific capacity and high discharge voltage, as the most promising cathode for high energy density lithium ion batteries, but suffers from serious cycling degradation. The present study revealed that the NCA cathode is stable with excellent cycling stability at voltages below 4.2 V, but suffers from serious degradation at voltages above 4.35 V. The characterization from SEM, TEM, XPS, FTIR, NMR, XRD and ICP as well as electrochemical measurements supported by theoretical calculations revealed that the trace of HF initially present in battery grade electrolytes likely induces the cycling stability degradation of the nickel-rich NCA cathode via accelerating the electrolyte decomposition. Our further research demonstrated that such cycling stability degradation can be eliminated through applying diethyl phenylphosphonite (DEPP) as an electrolyte additive, as DEPP is capable of shielding HF besides its ability to construct a protective cathode interphase, resulting in an excellent cycling stability of the nickel-rich NCA cathode.

Converting detrimental HF in electrolytes into a highly fluorinated interphase on cathodes

A highly fluorinated cathode–electrolyte-interphase is constructed on a Li-rich transition metal oxide via a unique additive approach, which significantly improves the cycling stability of Li-ion batteries based on such a high energy density cathode material. Physical characterization and electrochemical measurements aided by theoretical calculations reveal that the silane molecule with an unsaturated functionality effectively scavenges harmful hydrogen fluoride (HF) from the electrolyte and forms a complex, which undergoes preferential oxidation on the cathode surface in the initial charging and eventually delivers the fluorine species to the interphase. This understanding of the fundamental relationship between the additive structure and interfacial chemistry provides inspiration for the rational design of more effective electrolyte additives for more aggressive next-generation battery chemistries.

Porous Ni 0.1 Mn 0.9 O 1.45 microellipsoids as high-performance anode electrocatalyst for microbial fuel cells

A novel bi-component composite of porous self-assembled micro-/nanostructured Ni0.1Mn0.9O1.45 microellipsoids as high-performance anode electrocatalyst for microbial fuel cells (MFCs) is successfully synthesized via a simple coprecipitation reaction in microemulsion and calcination method in air atmosphere. The morphology and structural characterization indicate that the as-fabricated Ni0.1Mn0.9O1.45 product is consist of Mn2O3 and NiMn2O4 (n(Mn2O3): n(NiMn2O4) = 0.35: 0.1) and has a porous microellipsoidal morphology. The microellipsoids are compose of numerous layered micro-/nanostructured blocks and the special porous microellipsoids structure of Ni0.1Mn0.9O1.45 offers a large specific surface area for bacteria adhesion. The porous Ni0.1Mn0.9O1.45 microellipsoids as anode electrocatalyst for MFCs exhibits excellent electrocatalytic activity to promote the extracellular electron transfer (EET) between the anode and bacteria, hence improves the performance of MFC. The MFC equipped with Ni0.1Mn0.9O1.45/CF anode achieves a maximum power density of 1.39 ± 0.02Wm-2, is significantly higher than that of commercial carbon felt anode. This work proposes a new method for the synthesis of high-performance and environmentally friendly anode electrocatalyst for MFCs.