RESUMEN
Prelithiation in a graphite anode is widely considered as an effective strategy to compensate for the lithium loss due to the formation of the solid electrolyte interphase (SEI), thus improving the cycle life of lithium-ion batteries (LIBs). However, less attention has been paid to the difference of the SEI established by prelithiation from that resulting from the charging process. To address this issue, a prelithiated graphite anode is prepared by thermal contact and its performances are investigated by electrochemical measurements and spectral characterizations. It is found that the significantly improved initial coulombic efficiency (ICE) and cyclic stability of the graphite anode by prelitiation are attributed to the formation of LiF-rich SEI. Different from the charging process that favors decomposition of solvents and results in a SEI mainly consisting of organic and inorganic carbonates, prelithiation is beneficial for the reduction of LiPF6 and results in a LiF-rich SEI that presents high stability and robustness, enabling the graphite anode with significantly improved cyclic stability.
RESUMEN
The nickel-rich cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) is deemed as a prospective material for high-voltage lithium-ion batteries (LIBs) owing to its merits of high discharge capacity and low cobalt content. However, the unsatisfactory cyclic stability and thermostability that originate from the unstable electrode/electrolyte interface restrict its commercial application. Herein, a novel electrolyte composed of a polyethylene (PE) supported poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) based gel polymer electrolyte (GPE) strengthened by a film-forming additive of 3-(trimethylsilyl)phenylboronic acid (TMSPB) is proposed. The porous structure and good oxidative stability of the P(VdF-HFP)/PE membrane help to expand the oxidative potential of GPE to 5.5 V compared with 5.1 V for the liquid electrolyte. The developed GPE also has better thermal stability, contributing to improving the safety performance of LIBs. Furthermore, the TMSPB additive constructs a low-impedance and stable cathode electrolyte interphase (CEI) on the NCM811 cathode surface, compensating for GPE's drawbacks of sluggish kinetics. Consequently, the NCM811 cathode matched with 3% TMSPB-containing GPE exhibits remarkable cyclicity and rate capability, maintaining 94% of its initial capacity after 100 cycles at a high voltage range of 3.0-4.35 V and delivering a capacity of 133.5 mAh g-1 under 15 C high current rate compared with 68% and 75.8 mAh g-1 for the one with an additive-free liquid electrolyte. By virtue of the enhanced stability of the NCM811cathode, the cyclability of graphite||NCM811 full cell also increases from 48 to 81% after 100 cycles. The incorporation of P(VdF-HFP)-based GPE and TMSPB electrolyte additive points out a viable and convenient pathway to unlock the properties of high energy density and satisfactory safety for next-generation LIBs.
RESUMEN
Compared with other commercial cathode materials, the LiNi0.8Co0.1Mn0.1O2 cathode (NCM811) has high specific capacity and a relatively low cost. Nevertheless, the higher nickel content in NCM811 leads to an extremely unstable interface between the electrode and the electrolyte, resulting in inferior cyclic stability of the corresponding cell. Use of film-forming additives is regarded as the most feasible and economic approach to construct a stable interface on the NCM811 cathode. However, less effective electrolyte additives have been reported to date. Herein, we propose a valid film-forming electrolyte additive, 2,4,6-triphenyl boroxine (TPBX), for application in a high-voltage NCM811 cathode. Experimental and computational results reveal that the TPBX additive can be preferentially oxidized to generate a highly stable and conductive cathode electrolyte interface (CEI) layer on the NCM811 cathode, which efficiently suppresses the detrimental side reaction and improves the electrochemical performance eventually. In detail, the cyclic stability of the Li/NCM811 half-cell is enhanced from 57% (without additive) to 78% (with 5% TPBX) after 200 cycles at 1C between 3.0 and 4.35 V. At a high current rate of 15C, the TPBX-containing electrode delivers a capacity of about 135 mAh g-1, which is much higher than that of the electrode without the additive (80 mAh g-1). Interestingly, the TPBX is also reduced earlier than the ethylene carbonate (EC) solvent to form an ionically conductive solid electrolyte interface (SEI) film on the graphite anode. Due to the CEI layer on the cathode and the SEI film on the anode simultaneously formed by the TPBX additive, the cyclic performance of the graphite/LiNi0.8Co0.1Mn0.1O2 full cell is enhanced. Therefore, the incorporation of the TPBX additive into the electrolyte provides a convenient method for the commercial application of the high-energy-density NCM811 cathode in high-voltage lithium-ion batteries.
RESUMEN
Li dendrite growth due to uncontrolled Li plating/stripping processes has been a challenge for the application of Li metal anodes in high energy secondary batteries. A novel strategy is proposed in this work to address this issue, which is based on simultaneously regulating Li ion (Li+) flux and Li metal surface activity by a terpolymer cladding that orients the Li+ flux and mitigates the side reactions for Li plating/striping. This cladding provides the Li anode with dendrite-free surface morphology and enhanced electrochemical performances. Stable cycling of 800 and 1400 h is achieved for Li symmetric cells in carbonate-based and ether-based electrolytes, respectively. In addition, the asymmetric Li-LiFePO4 and Li-sulfur cells attain a prolonged cycle lifespan with reduced interfacial resistance after cycling. These performances might be further improved by more delicately designing the polymer structure and assembling the cladding, which might help fulfill the practical applications of Li anodes in high energy batteries.
RESUMEN
A novel electrolyte additive, 1-(2-cyanoethyl) pyrrole (CEP), has been investigated to improve the electrochemical performance of graphite/LiNi0.6Co0.2Mn0.2O2 cells cycling up to 4.5 V vs Li/Li+. The 4.5 V cycling results present that after 50 cycles, up to 4.5 V capacity retention of the graphite/LiNi0.6Co0.2Mn0.2O2 cell is improved significantly from 27.4 to 81.5% when adding 1% CEP to baseline electrolyte (1 M LiPF6 in EC/EMC 1:2, by weight). Ex situ characterization results support the mechanism of CEP for enhancing the electrochemical performance. On one hand, the significant enhancement is ascribed to a formed superior cathode interfacial film by preferential oxidation of CEP on the cathode electrode surface suppressing electrolyte decomposition at high voltage. On the other hand, the duo Lewis base functional groups can effectively capture dissociation product PF5 from LiPF6 with the presence of an unavoidable trace amount of water or aprotic impurities in the electrolyte. Thus this mitigates the hydrofluoric acid (HF) generation that leads to the reduction of transition-metal dissolution in the electrolyte upon cycling at high voltage. The theoretical modeling suggests that CEP has a mechanism of stabilizing electrolyte via combination of -C≡N: functional group and H2O. The work presented here also shows nuclear magnetic resonance spectra analysis to prove the capability of CEP reducing HF generation and X-ray photoelectron spectroscopy analysis to observe cathode surface composition.
RESUMEN
In this paper, MnO2 nanoboxes coated with poly(3,4-ethylenedioxythiophene) film (denoted as MnO2@PEDOT) are investigated as an anode material in lithium-ion batteries. The MnO2 nanoboxes are developed through the surface chemical oxidation decomposition of MnCO3 cubes and the subsequent removal of their remaining cores. PEDOT is coated on the surface of MnO2 nanoboxes via in situ polymerization of 3,4-ethylenedioxythiophene. The charge-discharge tests demonstrate that this special configuration endows the resulting MnO2@PEDOT with remarkable electrochemical performances, that is a reversible capacity of 628 mA h g-1 after 850 cycles at a current density of 1000 mA g-1 and a rate capacity of 367 mA h g-1 at 3000 mA g-1. The results indicate that the nanoboxes provide the paths for Li-ion diffusion, the reaction sites for Li-ion intercalation/deintercalation and the space to buffer the volume change during the charge-discharge process, while the conductive polymer ensures the structural stability and improves the electronic conductive property of MnO2.
RESUMEN
To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.
RESUMEN
Layered cathodes for lithium-ion battery, including LiCo1-x-yNixMnyO2 and xLi2MnO3·(1-x)LiMO2 (M = Mn, Ni, and Co), are attractive for large-scale applications such as electric vehicles, because they can deliver additional specific capacity when the end of charge voltage is improved to over 4.2 V. However, operation under a high voltage might cause capacity decaying of layered cathodes during cycling. The failure mechanisms that have been given, up to date, include the electrolyte oxidation decomposition, the Ni, Co, or Mn ion dissolution, and the phase transformation. In this work, we report a new mechanism involving the exfoliation of layered cathodes when the cathodes are performed with deep cycling under 4.5 V in the electrolyte consisting of carbonate solvents and LiPF6 salt. Additionally, an electrolyte additive that can form a cathode interface film is applied to suppress this exfoliation. A representative layered cathode, LiCoO2, and an interface film-forming additive, dimethyl phenylphosphonite (DMPP), are selected to demonstrate the exfoliation and the protection of layered structure. When evaluated in half-cells, LiCoO2 exhibits a capacity retention of 24% after 500 cycles in base electrolyte, but this value is improved to 73% in the DMPP-containing electrolyte. LiCoO2/graphite full cell using DMPP behaves better than the Li/LiCoO2 half-cell, delivering an initial energy density of 700 Wh kg -1 with an energy density retention of 82% after 100 cycles at 0.2 C between 3 and 4.5 V, as compared to 45% for the cell without using DMPP.
RESUMEN
Nanolayered lithium-rich oxide doped with spinel phase is synthesized by acidic sucrose-assistant sol-gel combustion and evaluated as the cathode of a high-energy-density lithium ion battery. Physical characterizations indicate that the as-synthesized oxide (LR-SN) is composed of uniform and separated nanoparticles of about 200 nm, which are doped with about 7% spinel phase, compared to the large aggregated ones of the product (LR) synthesized under the same condition but without any assistance. Charge/discharge demonstrates that LR-SN exhibits excellent rate capability and cyclic stability: delivering an average discharge capacity of 246 mAh g(-1) at 0.2 C (1C = 250 mA g(-1)) and earning a capacity retention of 92% after 100 cycles at 4 C in the lithium anode-based half cell, compared to the 227 mA g(-1) and the 63% of LR, respectively. Even in the graphite anode-based full cell, LR-SN still delivers a capacity of as high as 253 mAh g(-1) at 0.1 C, corresponding to a specific energy density of 801 Wh kg(-1), which are the best among those that have been reported in the literature. The separated nanoparticles of the LR-SN provide large sites for charge transfer, while the spinel phase doped in the nanoparticles facilitates lithium ion diffusion and maintains the stability of the layered structure during cycling.
RESUMEN
Phenyl vinyl sulfone (PVS) as a novel electrolyte additive is used to construct a protective interface film on layered lithium-rich cathode. Charge-discharge cycling demonstrates that the capacity retention of Li(Li0.2Mn0.54Ni0.13Co0.13)O2 after 240 cycles at 0.5 C between 2.0 and 4.8 V (vs Li/Li+) reaches about 80% by adding 1 wt % PVS into a standard (STD) electrolyte, 1.0 M LiPF6 in EC/EMC/DEC (3/5/2 in weight). This excellent performance is attributed to the special molecular structure of PVS, compared to the additives that have been reported in the literature. The double bond in the molecule endows PVS with preferential oxidizability, the aromatic ring ensures the chemical stability of the interface film, and the sulfur provides the interface film with ionic conductivity. These contributions have been confirmed by further electrochemical measurements, theoretical calculations, and detailed physical characterizations.