Enhanced Capacity Retention Research Articles

Improved Electrochemical Performance of NH[sub 4]AlF[sub 4]-Coated LiCoO[sub 2] Cycled over 4.5 V

Cathode coatings are being developed to improve lithium-ion batteries. In this effort, particles were coated with by a simple dry-coating process to enhance capacity retention on a 4.5 V cutoff cycling. Compared with pristine , this coating greatly improved the electrode cyclability and rate capability. Electrochemical impedance spectroscopy and a cobalt dissolution test showed that the coating protected the particle surface from HF and, thus, suppressed the increase in interfacial impedance between the cathode and electrolyte that occurred with an uncoated cathode material.

Spray pyrolyzed NiO–C nanocomposite as an anode material for the lithium-ion battery with enhanced capacity retention

NiO–C nanocomposite was prepared by a spray pyrolysis method using a mixture of Ni(NO 3) 2 and citric acid solution at 600 °C. The microstructure and morphology of the NiO–C composite were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) mapping, and thermogravimetric analysis (TGA). The results showed that the NiO nanoparticles were surrounded by amorphous carbon. Electrochemical tests demonstrated that the NiO–C nanocomposites exhibited better capacity retention (382 mAh g − 1 for 50 cycles) than that of pure NiO (141 mAh g − 1 for 50 cycles), which was also prepared by spray pyrolysis using only Ni(NO 3) 2 as precursor. The enhanced capacity retention can be mainly attributed to the NiO–C composite structure, composed of NiO nanoparticles surrounded by carbon, which can accommodate the volume changes during charge–discharge and improve the electrical conductivity between the NiO nanoparticles.

Superior Capacity Retention Sn–Ni–Fe–C Composite Anodes for Lithium-Ion Batteries

Sn-Ni-Fe-C composite anodes have been synthesized by a mechanochemical reaction of Sn with Ni-C and Fe-C composites and characterized. The Sn-Ni-Fe-C composite consisting of nanostructured Sn 4 Ni 3 , Sn 2 Fe, and SnFe along with carbon exhibits excellent capacity retention with a capacity of over 400 mAh/g. X-ray diffraction characterization of the electrodes reveals that while Sn 2 Fe decomposes completely during the lithiation process, both Sn 4 Ni 3 and SnFe decompose only partially. The enhanced capacity retention of Sn-Ni-Fe-C compared to that of Sn is attributed to the buffering effect provided by Sn 4 Ni 3 and SnFe and their effectiveness in suppressing the Sn grain growth during cycling.

Enhanced capacity retention of Co and Li doubly doped LiMn 2O 4

Cobalt and lithium doubly doped spinel LiMn 2O 4 have been synthesized by a solid state reaction. The effect of Co and Li doped spinel LiMn 2O 4 was investigated. The undoped and doped spinels were characterised by means of X-ray diffraction (XRD), inductively coupled plasma/atomic emission spectrometer (ICP/AES) and electrochemical test. The results showed that the doped spinel exhibited superior cycling performance than undoped spinel. The capacity retention of graphite/doped spinel full cell was more than 86% after 1000 cycles (2 C rate) at room temperature, which maintained 85% after 100 cycles (1 C rate) at 55 °C. The differential capacity profiles on doped spinel cathode are more fixed than undoped spinel cathode. Compared with undoped spinel, Mn dissolution into electrolyte at 55 °C was reduced by 41%, the lattice parameter difference Δ a was reduced by 82% on doped spinel cathode after cycling. The greatly suppressed structural change and manganese dissolution are responsible for the improved cycling performance on cobalt and lithium doubly doped spinel.

Layered Oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1, 2, and 3) as Insertion Hosts for Li Ion Batteries

The layered oxysulfides Sr2MnO2Cu2m-0.5Sm+1 (m = 1-3) consist of alternating perovskite-type Sr2MnO2 layers and copper sulfide layers. The copper ions can be replaced electrochemically and reversibly by Li. The lithiated materials were studied by Li MAS NMR, and Li resonances were observed with shifts that could be rationalized based on the number of sulfide layers. The materials were cycled versus Li and showed enhanced capacity retention in comparison to pure Cu2S; the good electrochemical performance was ascribed to the presence of the layered framework structure and rapid Li+ and Cu+ conductivity in the sulfide layers.

Study of the electrochemical properties of Ga-doped LiNi 0.8Co 0.2O 2 synthesized by a sol–gel method

The effects of gallium doping on the structure and electrochemical properties of LiNi 0.8Co 0.2O 2 were investigated by X-ray diffraction, cyclic voltammetry and charge-discharge tests. LiNi 0.8Co 0.2− x Ga x O 2 ( x = 0.01, 0.03, 0.05) was synthesized using a sol–gel method and it showed the average particle size less than 1 μm in diameter. Results showed that gallium-doping had no effect on the crystal structure (α-NaFeO 2) of the cathode material in the range x ≤ 0.05. On the other hand, two transitions at 3.7–3.9 and 4.2–4.7 V observed during the cycle test were merged into one when the amount of gallium doping increases to 0.05, implying that the enhanced capacity retention with gallium doping is attributed to the suppression of the phase transition of the cathode. However, the increase of gallium content in LiNi 0.8Co 0.2O 2 slightly decreases the initial discharge capacity.

Effect of Copper Doping on Intercalation Properties of Amorphous Manganese Oxides Prepared by Oxidation of Mn(II) Precursors

Copper-doped amorphous manganese oxides were synthesized via a room-temperature aqueous solution route involving oxidation of Mn(II) precursors. Doping of copper ions did not significantly affect the low rate specific capacity or the intrinsic lithium intercalation capacity of the amorphous materials. However, even a small amount of copper doping dramatically increased the specific capacity at high rates. Larger amounts of copper doping also significantly enhanced capacity retention upon cycling. For an amorphous manganese dioxide doped with 0.18 Cu per Mn, a specific capacity of 275 mAh/g was attained between 4.0 and 1.5 V vs. Li + /Li at a high discharge/charge rate of C/5 (0.78 mA/cm 2 ), with capacity fading of less than 0.5% per cycle upon cycling. It is believed that copper doping has the dual effect of both improving the lithium intercalation kinetics and stabilizing the local structure of the amorphous materials during lithium intercalation and cycling.