Silicon oxide (SiO
x
) has received remarkable attention as a next-generation battery material; however, the sudden decrease in the cycling retention constitutes a significant challenge in ...facilitating its application. Tris(2,2,2-trifluoroethyl) phosphite (TTFP), which can control parasitic reactions such as the pulverization of SiO
x
anode materials and electrolyte decomposition, has been proposed to improve the lifespan of the cell. The electrochemical reduction of TTFP results in solid-electrolyte interphase (SEI) layers that are mainly composed of LiF, which occur at a higher potential than the working potential of the SiO
x
anode and carbonate-based solvents. The electrolyte with TTFP exhibited a substantial improvement in cycling retention after 100 cycles, whereas the standard electrolyte showed acutely decreased retention. The thickness of the SiO
x
anode with TTFP also changed only slightly without any considerable delamination spots, whereas the SiO
x
anode without TTFP was prominently deformed by an enormous volume expansion with several internal cracks. The cycled SiO
x
anode with TTFP exhibited less increase in resistance after cycling than that in the absence of TTFP, in addition to fewer decomposition adducts in corresponding X-ray photoelectron spectroscopy (XPS) analyses between the cycled SiO
x
anodes. These results demonstrate that TTFP formed SEI layers at the SiO
x
interface, which substantially reduced the pulverization of the SiO
x
anode materials; in addition, electrolyte decomposition at the interface decreased, which led to improved cycling retention.
Graphical abstract
Ni-rich lithium nickel–cobalt-manganese oxides (NCM) are considered the most promising cathode materials for lithium-ion batteries (LIBs); however, relatively poor cycling performance is a bottleneck ...preventing their widespread use in energy systems. In this work, we propose the use of a dually functionalized surface modifier, calcium sulfate (CaSO
4
, CSO), in an efficient one step method to increase the cycling performance of Ni-rich NCM cathode materials. Thermal treatment of LiNi
0.8
Co
0.1
Mn
0.1
O
2
(NCM811) cathode materials with a CSO precursor allows the formation of an artificial Ca- and SO
x
-functionalized cathode–electrolyte interphase (CEI) layer on the surface of Ni-rich NCM cathode materials. The CEI layer then inhibits electrolyte decomposition at the interface between the Ni-rich NCM cathode and the electrolyte. Successful formation of the CSO-modified CEI layer is confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy analyses, and the process does not affect the bulk structure of the Ni-rich NCM cathode material. During cycling, the CSO-modified CEI layer remarkably decreases electrolyte decomposition upon cycling at both room temperature and 45 °C, leading to a substantial increase in cycling retention of the cells. A cell cycled with a 0.1 CSO-modified (modified with 0.1% CSO) NCM811 cathode exhibits a specific capacity retention of 90.0%, while the cell cycled with non-modified NCM811 cathode suffers from continuous fading of cycling retention (74.0%) after 100 cycles. SEM, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) results of the recovered electrodes demonstrate that undesired surface reactions such as electrolyte decomposition and metal dissolution are well controlled in the cell because of the artificial CSO-modified CEI layer present on the surface of Ni-rich NCM811 cathodes.
Graphical abstract
A surface coating of SiO2 is applied to a Ni rich LiNi0.6Co0.2Mn0.2O2 cathode material in a bid to improve its electrochemical and thermal properties. A uniform coating is achieved through a wet ...process using nano-sized SiO2 powder, and though the coated electrode is found to exhibit a reduced rate capability, its cycle performance at a high temperature of 60 °C is greatly enhanced. The effect of this SiO2 coating is further investigated by electrochemical impedance spectroscopy, which confirms that it suppresses the growth of interfacial impedance during progressive cycles. The SiO2 coating also demonstrates good HF scavenging ability, producing a subsequent reduction in the degradation of the active core material. The thermal properties of LiNi0.6Co0.2Mn0.2O2 are also improved by the SiO2 coating due to a reduction in the direct contact between the electrode and electrolyte. On the basis of these results, SiO2 coating is considered a viable surface modification method for improving the electrochemical and thermal properties of LiNi0.6Co0.2Mn0.2O2.
•Nano-sized SiO2 was uniformly coated on the surface of LiNi0.6Co0.2Mn0.2O2 cathode.•Thermal stability and cycle performance are improved by SiO2 coating.•EIS results suggest that side reaction on interface is suppressed by SiO2 coating.•SiO2 coating shows significant HF scavenging effect.
•Reaction characteristics of additives for high-voltage batteries are investigated.•The additives themselves have difficulty decomposing even in the cation state.•HF- and LiF-scavenging reactions of ...their neutral and cation species are favorable.•The additives can remove HF and LiF in electrolyte and on electrode, respectively.•Particularly, direct LiF-scavenging ability on the cathode surface is excellent.
Tris(trimethylsilyl) phosphite, tris(trimethylsilyl) borate, and tris(trimethylsilyl) phosphate are well known as effective electrolyte additives that noticeably improve the electrochemical performance of the cathode material in high-voltage lithium-ion batteries. It is essential to understand the reaction characteristics of such additives for developing novel electrolyte additives for high-voltage batteries. This work reports the distinct reaction characteristics of the three popular additives via first-principles calculations of self-decomposition reactions and reactivity with HF and LiF that significantly degrade the cell performance. Spontaneous decomposition reactions of their neutral and cation species are all thermodynamically unfavorable, which indicates that the additives themselves have difficulty decomposing even in the cation state. The HF- and LiF-scavenging reactions of their neutral and cation species are all very favorable. Our results indicate that the strong reactivity of additives can efficiently remove the undesired molecules HF and LiF in the electrolyte and on the cathode surface, respectively. In particular, LiF-scavenging ability on the cathode surface is excellent.
Ni-rich layered oxides are promising cathode candidates for Li-ion batteries because of their high discharge capacity, high energy density, and low cost. However, poor cycling stability and thermal ...instability during cycling limit their commercial application in electric vehicles. To overcome these drawbacks, Ni-rich transition metal hydroxide precursors comprising a Ni-rich core and Ni-less surface region are successfully prepared in this study by a simple treatment process with dilute sulfuric acid. The final cathode materials have a compositional core-shell design, taking advantage of the stable cyclability and high thermal stability of the Ni-less surface layer as well as the high capacity of the Ni-rich core. The cycling stability of this Ni-rich cathode significantly improves after leaching, showing a capacity retention of 82.3% after 150 cycles at a rate of 0.5C and elevated temperature of 60 °C, much higher than that of a pristine Ni-rich cathode (65.4%). Furthermore, the thermal stability of the prepared Ni-rich cathode improves remarkably after leaching. These results suggest that the prepared cathode meets the energy storage demands of electric vehicles in terms of energy density, power, and cycling life; therefore, it is a promising cathode material for electric vehicle applications.
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•NCM hydroxide with a core-shell composition is achieved by simple acid treatment.•Acid treatment leads to the partial Ni dissolution on the surface of NCM hydroxide.•The Ni-less surface layer results in stable cyclability and structural stability.
Nickel-rich layered transition metal oxides have been highlighted as advanced cathode materials; however, their poor cycling performance at elevated temperatures is a critical hurdle that limits the ...expansion of their applications. We propose a novel approach for the development of a chemically induced cathode–electrolyte interphase on cathodes using a lithium tetra(trimethylsilyl) borate as a functional precursor. This precursor contains a silyl-borate functional group that forms the cathode–electrolyte interphase layer via chemical reactions, which mitigates electrolyte decomposition and scavenges fluoride species. The precursor is prepared by a convenient one-step synthesis and it readily forms a nanoscale artificial cathode–electrolyte interphase layer through chemical reactions with cathode material during the mixing process used for the preparation of cathode slurries. Our first-principles calculations reveal a thermodynamically favorable reaction between lithium tetra(trimethylsilyl) borate and the fluoride species. We demonstrate that the artificial cathode–electrolyte interphase layer effectively mitigates electrolyte decomposition and the dissolution of transition metal components, thereby improving the interfacial stability of cathodes. As a result, a cell cycled with lithium tetra(trimethylsilyl) borate-modified cathode material shows comparable cycling retention at room temperature and much improved cycling performance at a high temperature after 100 cycles.
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•Artificial CEI layer was formed on Ni-rich NCM cathode by lithium salt, LTB.•CEI precursor, LTB, was synthesized by simple and convenient one-step process.•Chemical reactions of LTB with Ni-rich NCM cathode afforded nanoscale CEI layer.•Chemically-induced CEI layers improved surface stability of NCM cathode.•LTB-modified CEI layers allowed stable cycling performances at high temperature.
Although the exceptional theoretical specific capacity (1672 mAh g−1) of elemental sulfur makes lithium–sulfur (Li–S) batteries attractive for upcoming rechargeable battery applications (e.g., ...electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li–S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO3 or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal‐air batteries) that suffer from cross‐contamination of charged species between both electrodes.
Poling for polysulfide rejection: The fatal shuttling process in lithium–sulfur batteries is effectively suppressed by “poled” BaTiO3 or BTO particles coated on a poly(ethylene) separator. The permanent dipoles of poled BTO particles repel polysulfides via electrostatic repulsion. The coating of BTO particles also provides a resistance against thermal shrinkage of the polyethylene separator at high temperature, thus enhancing the safety of the given cell.
Nickel-rich nickel-cobalt-manganese layered oxides receive significant attention as advanced cathode materials, however, they suffer from poor cycling performance at elevated temperature because of ...surface instability. In this study, we develop nickel-rich cathode materials modified by an artificial cathode-electrolyte interphase layer embedding silyl ether functional groups. An artificial cathode-electrolyte interphase layer-functionalized nickel-rich cathode materials are simply synthesized via a wet-coating-based thermal treatment using a dimethoxydimethylsilane as an organic precursor. The task-specific silyl ether functional groups are effective in selectively scavenging nucleophilic fluoride species, which potentially triggers the dissolution of transition metal components into the electrolyte. Microscopic analyses indicate that the artificial cathode-electrolyte interphase layer is well developed on the surface of the nickel-rich cathode materials with several nanometers-thickness. The cells cycled with functionalized nickel-rich cathodes exhibit much higher cycling retentions (∼70.0%) than the cell cycled with bare nickel-rich cathode (47.1%) at high temperature. Additional systematical analyses indicate that the artificial cathode-electrolyte interphase layers effectively mitigate the electrolyte decomposition and the dissolution of transition metal components, thereby improving the cycling behavior of the cell on the basis of increased interfacial stability of nickel-rich cathode materials.
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•Artificial CEI layer was introduced by Si-based precursor on Ni-rich NCM cathode.•Si-based artificial CEI layer was provided by wet coating-based one-step process.•Task-specific Si–O functional groups on CEI layer were effective in F− scavenging.•Si-based CEI layer improved interfacial stability of Ni-rich NCM cathode.•Si-based artificial CEI layer allowed enhanced cycle retention at high temperature.
In this study, manganese orthophosphate (Mn3(PO4)2) is investigated as a new coating material for the Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode with the aim of improving its thermal properties. A sol–gel ...process is employed to achieve a uniform coating of nano–sized crystalline Mn3(PO4)2. The coated electrode is found to exhibit an improved rate capability at high current drain, and cycle performance is enhanced at a high temperature of 60°C. The effect of the Mn3(PO4)2 coating thus formed is further investigated by AC impedance spectroscopy, the results of which confirm that interfacial impedance is significantly decreased even in the initial cycles, and the growth of impedance is successfully suppressed during progressive cycles. The thermal stability of LiNi0.6Co0.2Mn0.2O2 is also improved by the Mn3(PO4)2 coating, because of the high structural stability attributed to strong PO4 covalent bonds. On the basis of these results, the Mn3(PO4)2 coating is proposed as a viable surface modification method for the enhancement of the electrochemical and thermal properties of LiNi0.6Co0.2Mn0.2O2.
Radical‐scavenging Al2O3‐tris(2,4,6‐trimethylphenyl) phosphine (TMPP)‐functionalized polyethylene (PE) separator is modified by preparation of the Al2O3‐TMPP composites and embedding them onto the PE ...separator by dip‐coating process. Scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, and Fourier‐transform infrared spectroscopy analyses indicate that Al2O3‐TMPP is well coated onto the PE separator. The Al2O3‐TMPP‐embedded PE separator exhibits a lower contact angle and higher electrolyte uptake than the bare PE separator, indicating a more hydrophilic surface is developed in the Al2O3‐TMPP‐embedded PE separator. The cell cycled with the Al2O3‐TMPP‐embedded PE separator exhibits stable cycling behavior after 150 cycles at high temperature (59.8%) while the cell cycled with a bare PE separator shows a continuous decrease in cycling retention (47.1%). The use of the Al2O3‐TMPP‐embedded PE separator is therefore an effective way to improve the cell cycling retention because it can effectively lower the radical concentration via a chemical scavenging process.
Tris(2,4,6‐trimethylphenyl) phosphine (TMPP) is firstly embedded to surface of Al2O3 and Al2O3‐TMPP composite is coated onto polyethylene (PE) separator via dip‐coating process. The cell cycled with the Al2O3‐TMPP‐embedded PE separator exhibits stable cycling behavior after 150 cycles because the Al2O3‐TMPP‐embedded PE separator effectively removes the radical species in the cell via a chemical scavenging reaction.
