A cathode material of an electrically conducting carbon‐LiMnPO4 nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the ...physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO4 electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 °C. This electrode delivers a discharge capacity of 158 mAh g−1 at 1/20 C, 126 mAh g−1 at 1 C, and 107 mAh g−1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confirm that the carbon particles surrounding the LiMnPO4 protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C‐LiMnPO4 electrode are also verified by electrochemical impedance spectroscopy.
The addition of acetylene black (AB) carbon to a nanostructured C‐LiMnPO4 cathode material results in an extraordinary electrode material for a lithium cell with very high reversible capacity and an excellent cycle life. The composite can easily be made by ultrasonic spray pyrolysis followed by ball milling. Microscopic studies confirm that the carbon particles protect the cathode materials from dissolution.
The reaction mechanism of α‐MnO2 having 2×2 tunnel structure with zinc ions in a zinc rechargeable battery, employing an aqueous zinc sulfate electrolyte, was investigated by in situ monitoring ...structural changes and water chemistry alterations during the reaction. Contrary to the conventional belief that zinc ions intercalate into the tunnels of α‐MnO2, we reveal that they actually precipitate in the form of layered zinc hydroxide sulfate (Zn4(OH)6(SO4)⋅5 H2O) on the α‐MnO2 surface. This precipitation occurs because unstable trivalent manganese disproportionates and is dissolved in the electrolyte during the discharge process, resulting in a gradual increase in the pH value of the electrolyte. This causes zinc hydroxide sulfate to crystallize from the electrolyte on the electrode surface. During the charge process, the pH value of the electrolyte decreases due to recombination of manganese on the cathode, leading to dissolution of zinc hydroxide sulfate back into the electrolyte. An analogous phenomenon is also observed in todorokite, a manganese dioxide polymorph with 3×3 tunnel structure that is an indication for the critical role of pH changes of the electrolyte in the reaction mechanism of this battery system.
The pH matters: Investigation of the reaction mechanism of tunneled manganese dioxide with zinc ions reveals that contrary to the conventional belief that zinc ions intercalate into the tunnels, a series of conversion reactions involving active manganese dissolution and concomitant electrolyte pH change lead to the reversible formation of layered zinc hydroxide sulfate.
In this study we report the effects of the Ni content on the electrochemical properties and the structural and thermal stabilities of LiNixCoyMnzO2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) synthesized ...via a coprecipitation method. The electrochemical and thermal properties of LiNixCoyMnzO2 are strongly dependent on its composition. An increase of the Ni content results in an increase of specific discharge capacity and total residual lithium content but the corresponding capacity retention and safety characteristics gradually decreased. The structural stability is related to the thermal and electrochemical stabilities, as confirmed by X-ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. Developing an ideal cathode material with both high capacity and safety will be a challenging task that requires precise control of microstructure and physico-chemical properties of the electrode.
We studied the fundamental characteristics of the LiNixCoyMnzO2 electrodes in a wide range of Ni concentrations (1/3 ≤ x ≤ 0.85) for Li-ion battery. An increase of the Ni content results in an increase of capacity but the corresponding capacity retention and safety characteristics gradually decreased. Display omitted
► LiNixCoyMnzO2 were synthesized via a coprecipitation method. ► The electrochemical and thermal properties are dependent on their compositions. ► Increasing Ni content raises the capacity whereas increasing Mn content improves safety.
For the first time, we report the electrochemical activity of anatase TiO2 nanorods in a Na cell. The anatase TiO2 nanorods were synthesized by a hydrothermal method, and their surfaces were coated ...by carbon to improve the electric conductivity through carbonization of pitch at 700 °C for 2 h in Ar flow. The resulting structure does not change before and after the carbon coating, as confirmed by X-ray diffraction (XRD). Transmission electron microscopic images confirm the presence of a carbon coating on the anatase TiO2 nanorods. In cell tests, anodes of bare and carbon-coated anatase TiO2 nanorods exhibit stable cycling performance and attain a capacity of about 172 and 193 mAh g–1 on the first charge, respectively, in the voltage range of 3–0 V. With the help of the conductive carbon layers, the carbon-coated anatase TiO2 delivers more capacity at high rates, 104 mAh g–1 at the 10 C-rate (3.3 A g–1), 82 mAh g–1 at the 30 C-rate (10 A g–1), and 53 mAh g–1 at the 100 C-rate (33 A g–1). By contrast, the anode of bare anatase TiO2 nanorods delivers only about 38 mAh g–1 at the 10 C-rate (3.3 A g–1). The excellent cyclability and high-rate capability are the result of a Na+ insertion and extraction reaction into the host structure coupled with Ti4+/3+ redox reaction, as revealed by X-ray absorption spectroscopy.
A surface-modified O3-type NaNi 0.6 Co 0.2 Mn 0.2 O 2 cathode was synthesized by Al 2 O 3 nanoparticle coating using a simple dry ball-milling route. The nanoscale Al 2 O 3 particles (∼15 nm in ...diameter) densely covering the spherical O3-type NaNi 0.6 Co 0.2 Mn 0.2 O 2 cathode particles effectively minimized parasitic reactions with the electrolyte solution while assisting Na + migration. The proposed Al 2 O 3 coated NaNi 0.6 Co 0.2 Mn 0.2 O 2 cathode exhibited a high specific capacity of 151 mA h g −1 , as well as improved cycling stability and rate capability in a half cell. Furthermore, the Al 2 O 3 coated cathode was scaled up to a pouch-type full cell using a hard carbon anode that exhibited a superior rate capability and capacity retention of 75% after 300 cycles with a high energy density of 130 W h kg −1 . In addition, the post-mortem surface characterization of the cathodes from the long-term cycled full cells helped in identifying the exact mechanism of the surface reaction with the electrolyte and the reason for its subsequent degradation and showed that the nano-scale Al 2 O 3 coating layer was effective at resolving the degradation pathways of the cathode surface from hydrogen fluoride (HF) attack.
The surface of a LiNi0.8Co0.15Al0.05O2 cathode material was coated by a 50-nm thick AlF3 layer using a simple dry coating process. Although the initial discharge capacity of pristine and AlF3-coated ...LiNi0.8Co0.15Al0.05O2 was nearly same, the AlF3-coating significantly improved the electrochemical performances of LiNi0.8Co0.15Al0.05O2 in a full cell configuration (graphite anode), especially at an elevated temperature (55 °C). Furthermore, the AlF3-coated LiNi0.8Co0.15Al0.05O2 had better thermal stability than the pristine electrode. The improved electrochemical performance likely arose from the AlF3 coating layer which may have retarded the transition metal dissolution from HF attack. Electrochemical impedance spectroscopy and transmission electron microscopy provided direct evidence that the AlF3 coating layer suppressed the increase in charge transfer resistance and cathode material pulverization during cycling.
► The surface of NCA (LiNi0.8Co0.15Al0.05O2) was coated by AlF3 through dry process. ► The AlF3-coated NCA full cell showed excellent electrochemical performance. ► The AlF3-coated NCA had better thermal stability than the pristine electrode. ► AlF3 coating suppressed the increase in resistance and particle pulverization.
Nickel-rich layered lithium transition-metal oxides, LiNi(1-x)M(x)O(2) (M = transition metal), have been under intense investigation as high-energy cathode materials for rechargeable lithium ...batteries because of their high specific capacity and relatively low cost. However, the commercial deployment of nickel-rich oxides has been severely hindered by their intrinsic poor thermal stability at the fully charged state and insufficient cycle life, especially at elevated temperatures. Here, we report a nickel-rich lithium transition-metal oxide with a very high capacity (215 mA h g(-1)), where the nickel concentration decreases linearly whereas the manganese concentration increases linearly from the centre to the outer layer of each particle. Using this nano-functional full-gradient approach, we are able to harness the high energy density of the nickel-rich core and the high thermal stability and long life of the manganese-rich outer layers. Moreover, the micrometre-size secondary particles of this cathode material are composed of aligned needle-like nanosize primary particles, resulting in a high rate capability. The experimental results suggest that this nano-functional full-gradient cathode material is promising for applications that require high energy, long calendar life and excellent abuse tolerance such as electric vehicles.
Future generations of electric vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium ...batteries is mandatory while also maintaining similar or improved rate capability, lifetime, cost, and safety. The vast majority of electric vehicles that will appear on the market in the next 10 years will employ nickel-rich cathode materials, LiNi1–x–y Co x Al y O2 and LiNi1–x–y Co x Mn y O2 (x + y < 0.2), in particular. Here, the potential and limitations of these cathode materials are critically compared with reference to realistic target values from the automotive industry. Moreover, we show how future automotive targets can be achieved through fine control of the structural and microstructural properties.
Microscale C-Li4Ti5O12 particles with high tap density were synthesized by a simple solid-state reaction using TiO2, Li2CO3, and pitch. The effect of the carbon content on the physicochemical and ...electrochemical properties of this material was extensively studied. On calcination of the particles at high temperature in an inert atmosphere, the uniformly coated carbon layer from pitch inhibited the growth of primary particles, maintaining the spherical morphology, similar to the TiO2 precursor in size and shape, and also enabling partial reduction of the starting Ti4+ to Ti3+. Excellent electronic conductivity of the C-coated Li4Ti5O12 resulted from the presence of the highly conducting carbon coating layer and the mixed valence state of Ti3+ and Ti4+. Both the nanoporous morphology and highly conducting carbon coating layer in Li4Ti5O12 particles gave rise to ultra high rate capability.
