X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS) are used to demonstrate that V2O5 is successfully ...coated on LiNiO2-based materials. The V2O5 layer will react with Li impurities on surface, which will reduce the pH value and rapid moisture uptake ability of LiNiO2-based materials. Cells tests indicate that V2O5-coating layer works as HF inhibitor and/or HF scavenger, which contributes a significant improvement in cycling performance and storage characteristics in electrolyte. In the mean time, V2O5 acts as isolating layer when cathode material contacts with electrolyte especially cycling at high voltage. Structural analysis shows that V2O5-coating layer has more advantage over other oxide coating in delaying Ni3+/Ni2+ transformation and lithium extraction from bulk surface, which benefits from the properties of V2O5 reacting with LiOH/Li2CO3 impurities on surface.
Ether electrolytes exhibit better rate kinetics than carbonate ester electrolytes when used in several kinds of anode materials, especially in hard carbon (HC) for sodium‐ion batteries (SIBs). ...However, the mechanism causing the remarkable kinetics difference is still unclear. Here, a three‐electrode system is used first to eliminate the influence of polarization from the Na counter electrode. Then, there is systematic exploration from three steps of the electrode reaction process (Na+ storage in HC; de‐solvation; Na+ migration through solid electrolyte interphase (SE), and the underlying mysteries are uncovered. For Na+ storage in the bulk of the HC, it is found that two systems show the same storage mechanism and Na metallic nanoparticles will appear when discharged to 0.1 V. In addition, faster de‐solvation of the ether electrolyte is uncovered by three‐electrode temperature‐dependent EIS and solvation free energies calculation. Moreover, the difference of the SEI layers is unraveled by X‐ray photoelectron spectroscopy etching, scanning electron microscopy, and differential electrochemical mass spectrometry. Most importantly, by discriminating the impacts of the SEI layers and de‐solvation behavior, it can be concluded that the de‐solvation process is the rate‐controlling step of the electrode reaction process and is the main factor causing the kinetics differences between the two electrolytes. The research provides a clear mechanism to illuminate fast kinetics for ether electrolytes, which will promote its application in SIBs.
Hard carbon electrodes show the same Na+ ion storage mechanism in two electrolytes. Ether electrolytes are favorable for a faster de‐solvation process. Solid electrolyte interphase (SEI) layers with more inorganic component and uniform morphology also favor faster Na+ ion transport for ether electrolytes. The de‐solvation behavior has a more profound effect than the SEI layers and is the main factor inducing the difference in kinetics.
Poor storage property and the rapid moisture hinder the application of LiNi0.8Co0.1Mn0.1O2 due to the formation of Li2CO3/LiOH impurities and a spontaneous reduction of Ni3+ to Ni2+ on the surface. ...Alcohol washing is desirable to improve the electrochemical performance, storage characteristics and structural stability of LiNi0.8Co0.1Mn0.1O2. Electrochemical studies indicate that washed material exhibits a higher discharge capacity (148mAhg−1 at 8C) and better capacity retention at 2C (79.2% after 100 cycles) compared with the un-treated material after storage in air for 40 days. Inductively coupled plasma (ICP) tests show the amount of metal dissolution decreases compared with the un-washed sample. The Rietveld refinement results indicate that the Li/Ni cationic disorder can be reduced from 0.0714 to 0.0538 by alcohol washing after storage. Transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicate alcohol washing contributes LiNi0.8Co0.1Mn0.1O2 much resistant to H2O and CO2, which further reduce the formation of Li2CO3 and maintain structural stability during the storage process.
Tris(trimethylsilyl)phosphate (TMSP) is investigated as a novel film-forming additive for LiNi sub(0.5)Co sub(0.2)-Mn sub(0.3)O sub(2) cycling at high cut-off potential in LiPF sub(6)-based ...electrolyte. Linear sweep voltammetry (LSV) results reveal that TMSP oxidizes prior to the decomposition of carbonate solvents in electrolyte. When TMSP is incorporated into the electrolyte, the electrochemical performance of LiNi sub(0.5)Co sub(0.2)Mn sub(0.3)O sub(2) is enhanced significantly. The initial discharge capacity of LiNi sub(0.5)Co sub(0.3)Mn sub(0.3)O sub(2) cathode material cycling in the electrolyte with 1 % TMSP is increased from 173.4 to 191.0 mAh g super(-1) compared with that without TMSP between 3.0 and 4.5 V (vs. Li/Li super(+)) at 0.1 C(1 C = 170 mA g super(-1)). In addition, it exhibits a capacity-retention of 90.9% at 1 C after 100 cycles, while that without TMSP is 77.0%. TEM, XPS, and EIS analyses confirm that the film derived from TMSP protects LiNi sub(0.5)Co sub(0.2)Mn sub(0.3)O sub(2) material from eroding by HF effectively, and reduces the interface impedance.
To improve the stability of LiVPO4F electrode/electrolyte interface, Li3PO4 is used to modify LiVPO4F composite (P-LVPF) for the first time. Morphological characterization shows that LiVPO4F ...particles are wrapped by amorphous carbon and lithium ionic conductor Li3PO4 as the interlayer and outer layer, respectively. Compared to the pristine sample, the resultant P-LVPF exhibits greatly improved rate capability and elevated-temperature cycle performance when applied as the cathode material for lithium ion batteries. Specifically, the Li3PO4 modified sample specific capacity maintains 77.6% at 1 C after 100 cycles under 55 °C. Such improvement is attributed to the fact that the Li3PO4 coating layer not only acts as a good ionic conductor for LiVPO4F, but also serves as a physical barrier between electrode and electrolyte which can build a stable interface.
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•Li3PO4 coating builds stable LiVPO4F/electrolyte interface for the first time.•LiVPO4F coated with Li3PO4 shows enhanced cycle performance at 55 °C.•Li3PO4 is proposed to act as a physical barrier as well as a Li+ transfer media.
Self-discharge and transition metal dissolution weaknesses bother the application of LiNi0.5Mn1.5O4 cathode material due to the severe oxidation of electrolyte at the high voltage state. A novel ...additive, 1-propylphosphonic acid cyclic anhydride (PACA), is desirable to prevent this oxidation. CV and charge–discharge results reveal that adding 0.5% PACA can relieve the oxidation of electrolyte. Consequently, the self-discharge and transition metal dissolution are both suppressed effectively, which is validated by self-discharge tests, XPS, and EDX analyses. Moreover, using PACA as an additive enhances the capacity retention capability of LiNi0.5Mn1.5O4 at elevated temperatures significantly.
•1-Propylphosphonic acid cyclic anhydride (PACA) is investigated as an additive.•Self-discharge of LiNi0.5Mn1.5O4 is effectively suppressed by adding PACA into electrolyte.•Enhanced cycling performance of LiNi0.5Mn1.5O4 at elevated temperatures is achieved.•Reduced transition metal dissolution of LiNi0.5Mn1.5O4 by using PACA.
•LiNi1/3Co1/3Mn1/3O2 was firstly used as a coating layer for LiNi0.8Co0.1Mn0.1O2.•The coating layer is electrochemical active for insertion/de-insertion of lithium ions.•In the co-precipitation ...process, the coating materials mostly grew on the surface of the host material rather than nucleate alone in the solution.•The coated samples showed good cycling performance and rate capability.
A modified LiNi1/3Co1/3Mn1/3O2-coating process is introduced to improve the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (LNCM811). The coating process is carried on a precursor, Ni0.8Co0.1Mn0.1(OH)2 (NCM811), rather than on LNCM811. Unlike the electro-inert metal oxide coatings, the LiNi1/3Co1/3Mn1/3O2 (LNCM111) layer is electrochemically active and able to relieve reactions between the highly delithiated Li1−μNi0.8Co0.1Mn0.1O2 and the electrolyte on account of the decrease of nickel content in outer layer. The LNCM111-coated LNCM811 material shows superior electrochemical performance, with an initial discharge capacity of 153mAhg−1 and capacity retention of 90% after 100 cycles at 2C rate between 2.8 and 4.3V at 60°C.
Herein, we report a series of O3-type Na(Ni
1/3
Mn
1/3
Fe
1/3
)
1-x
Al
x
O
2
(
x
= 0, 0.03, 0.05, 0.07) oxides as sodium-ion battery cathode materials synthesized via spray pyrolysis method. The ...structure, morphology, and electrochemical performance of Na(Ni
1/3
Mn
1/3
Fe
1/3
)
1-x
Al
x
O
2
(
x
= 0, 0.03, 0.05, 0.07) are characterized by XRD, SEM, CV, and galvanostatic charge and discharge tests, respectively. Na(Ni
1/3
Mn
1/3
Fe
1/3
)
0.95
Al
0.05
O
2
delivers an initial discharge capacity of 145.4 mAh g
−1
at 0.1 C and exhibits a favorable reversible capacity about 128.4 mAh g
−1
after 80 cycles at 0.2 C, with the capacity retention of 77.5% at the voltage range of 2.0 to 4.2 V. XPS analysis reveals that Al-doping could alleviate the Jahn-Teller effect caused by Mn
3+
and enhance the structural stability of layered oxides. The results confirm that a small quantity of (5 at. %) Al-doping improves the structural stability of the material, therefore leading to the excellent electrochemical performance.
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