N-Allyl-N,N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive to

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Surfaces, Interfaces, and Applications

N-Allyl-N,N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive to Enhance the Interfacial Stability of Ni-rich Electrode for Lithium Ion Batteries Qinfeng Zheng, Lidan Xing, Xuerui Yang, Xiangfeng Li, Changchun Ye, Kang Wang, Qiming Huang, and Weishan Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b00913 • Publication Date (Web): 24 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018

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ACS Applied Materials & Interfaces

N-Allyl-N,N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive to Enhance the Interfacial Stability of Ni-rich Electrode for Lithium Ion Batteries Qinfeng Zhenga, Lidan Xing*a, Xuerui Yanga, Xiangfeng Lib, Changchun Yea, Kang Wanga, Qiming Huanga, Weishan Li*a a.

Engineering Research Center of MTEES (Ministry of Education), Research Center of BMET (Guangdong Province), Key Lab. of ETESPG (GHEI), and Innovative Platform for ITBMD (Guangzhou Municipality), School of Chemistry and Environment, South China Normal University, Guangzhou 510006, China

b. Guangzhou Institute of Energy Testing, Guangzhou 511447, China

Abstract Enhancing the electrode/electrolyte interface stability of high capacity LiNi0.8Co0.15Al0.05O2 (LNCA) cathode material is urgently required for its application in next generation lithium ion battery. Herein, we demonstrate that enhanced interfacial stability of LNCA can be achieved by simply introducing 2 wt. % N-Allyl-N,Nbis(trimethylsilyl)amine (NNB) electrolyte additive. Electrolyte oxidation reactions and transition metal ion dissolution are greatly suppressed in the electrolyte with NNB additive, leading to improved cyclic stability of LNCA from 72.8 % to 86.2 % after 300 cycles. The mechanism of NNB on improving the cyclic stability of LNCA has been verified to its excellent SEI film-forming capability. Moreover, the XRD and XPS results indicate that the NNB-derived Si-containing SEI film restrains the Li/Ni disorder of LNCA during cycling, which further improve the cyclic stability of Ni-rich LNCA. Importantly, charging/discharging test reveals that NNB additive effectively improve the cyclic stability of LNCA/graphite full-cell. Keywords: Lithium-ion battery; Ni-rich electrode; Electrolyte additive; N-Allyl-N,NBis(trimethylsilyl) amine; Interfacial stability. *Corresponding author: South China Normal University, Guangzhou 510006, China. Tel/fax: 86-2039310256. Email address: [email protected] (L.D); [email protected] (W.S)

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1. Introduction Lithium ion batteries (LIBs), mainly consisting of an electrolyte-soaked polymer separator sits between a graphite anode and lithium transition metal oxide cathode, have become the choice of power source for electric vehicles.1, 2 Next generation LIBs with higher energy density, greater safety and lower price are urgently needed to make electric vehicles a mass-market product. Developing novel cathode materials possessing higher specific capacity and operating potential have been proved to be the most economical and effective way to improve the energy density of LIBs. Among the proposed novel cathode materials, layered Ni-rich cathode LiNi0.8Co0.15Al0.05O2 (LNCA) is considered as one of the most seductive candidates because of its larger reversible specific capacity (200 mAh g-1 ，at 0.05C) comparing with conventional cathode materials1, 3, such as LiFePO4 (165 mAh g-1), LiMn2O4 (120 mAh g-1) and LiCoO2 (145 mAh g-1)1, 4. Unfortunately, the application of LNCA is hindered by its severe capacity decaying during cycling, which primarily caused by the instability of LNCA/electrolyte interface5. The high hygroscopicity of LNCA would react with air and moisture during storage, generating impurities, such as Li2CO3 and LiOH. Moreover, the impurities-containing LNCA further lowers its interfacial stability with electrolyte, resulting in high interfacial reaction resistance and poor cycle life. To improve the interfacial stability of LNCA/electrolyte, much effort has been made in the past few decades. Coating inert inorganic compounds on LNCA surface, including AlF3, SiO2, ZnO, FeF3, and Ni3PO4, etc, could enhance its interfacial stability6-10. However, it is difficult for current coating techniques to provide complete


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surface coating, which would leave small amount of un-coating LNCA exposing to electrolyte11-13. Application of film-forming electrolyte additive is another effective approach to enhance the electrode/electrolyte interfacial stability. The additive would decompose on the electrode surface previously to baseline electrolyte during charging/discharging, generating a complete dense passivation film to prevent the electronic contact of electrode electrolyte14. Surprisingly, to the best of our knowledge, few studies have been reported investigating the influence of electrolyte additives on the electrochemical performance of LNCA. Silicon-containing electrolyte additives, such as N,N-diethylamino trimethylsilane, tris(trimethylsilyl)borate,

hexa-methyl-disilazane, hepta-methyl-disilazane, tris(tri-

methylsilyl)phosphite and tris(trimethylsilyl)phosphate create Si-containing solid electrolyte interface (SEI) film on the layered oxide cathode surface, resulting in greatly improved cyclic performances of the cathodes15-24. In addition, in our recent work, we demonstrated that protective film with higher content of Si exhibits better capability on enhancing the interfacial stability of cathode/electrolyte during cycling25, indicating that Si-containing SEI film is beneficial to interfacial stability of electrode/electrolyte. A novel film-forming electrolyte additive N-Allyl-N,N-bis (trimethylsilyl)amine (NNB) (C9H23N2Si) is proposed herein according to our previous experience on screening film-forming additives for high voltage cathodes materials26-29. Theoretical and experimental characterization results show that the oxidation activity of NNB is obviously higher than that of baseline electrolyte, resulting in preferential oxidation of NNB additive during initial charging process. And importantly, the oxidation



decomposition of NNB-containing electrolyte creates an effective uniform SEI film on the LNCA surface, which greatly improves the cyclic stability of LNCA/Li half-cell and LNCA/graphite full-cell. 2. Experimental section 2.1 Electrodes, electrolytes preparation and cells assemblage The slurry of LNCA electrode consists of LiNi0.8Co0.15Al0.05O2 (Ningbo Jinhe New materials Co., Ltd.), poly (vinylidene difluoride) (PvdF) and acetylene carbon black (AB) (85: 5: 10 in weight), while slurry of graphite electrode contains artificial graphite, PVDF and AB (80:10:10 in weight). LNCA and graphite electrode was made via coating the above slurry on Al foil and Cu foil, respectively. The average mass loading of LNCA and graphite is 3.68 and 2.65 mg/cm2, respectively. The obtained electrodes were then dried in vacuum oven for electrochemical characterizations. The loading mass of the active material for LNCA/graphite full-cells were calculated according to the N/P values of 1.2 (N and P is the specific capacity of anode and cathode, respectively. In this case, 330 and 160 mAhg-1 for graphite and LNCA respectively.). N-Allyl-N,Nbis(trimethylsilyl)amine (NNB) (98%) additive was obtained from Alfa Industrial Inc, China. Carbonate solvents were acquired from Guangzhou Tianci Marerials Technoloogy Co. Ltd, China, including diethyl carbonate (DEC), ethylene carbonate (EC) and ethylene carbonate (EC). Baseline electrolyte was obtained via dissolving 1.0 M LiPF6 in the mixing solvents (DEC: EC: EMC=2: 3: 5, in weight). NNB-containing electrolytes were obtained via addition different amount NNB (1 wt. %, 2 wt.% and 5 wt.%) into the baseline electrolyte. Electrolyte preparations were finished in glove box


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(MBraun, Germany) filed with high-purity Ar. H2O and O2 content in the glove box was control below 0.1 ppm. LNCA/Li and graphite/Li 2025-coin cells were assembled using Celgard 2400 separator in the glove box. 2.2. Electrochemical and physical characterizations The LNCA/Li, graphite/Li and LNCA/graphite cells were charged/ discharged on LAND system (CT2001A, China). The LNCA/Li half-cells were cycled galvanostatically under 0.3 C (1C =180 mAh g-1) in initial three cycles and 1C for the subsequence cycles between 3.0 and 4.2 V, wherein constant potential at 4.2 V for 10 minutes. Rate capability was tested at various rates. The graphite/Li half-cells were cycled between 0.005 V and 2.5 V with initial three cycles at 0.1 C and rest cycles at 0.2 C (1 C =372 mAh g-1). LNCA/graphite full-cells were cycled at 0.2 C for the initial three cycles and 1C for the subsequent cycles. The charge/ discharge voltage range of full-cell is from 3 to 4.2V. Electrochemical impedance spectroscopy (EIS) was measured on electrochemical station (PGSTAT-30, Autolab Metrohm, Netherlands) with frequency varied from 105 to 10-2 Hz and voltage amplitude of 5 mV. All of the EIS measurement was performed at 4.2 V. linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were conducted on Solartro-1480 instrument (England). The sweep of LSV was 1 mV/s using three electrodes ‘V-type’ cell (platinum as working electrolyte, lithium as counter and reference electrode). CV was tested between 3.0 and 4.2 V under 0.1mV/s. Disassembling of the cycled cells were carried out in the glove box. DEC solvent was used to wash the cycled electrode for four times. Scanning electron microscopy



(SEM) and transmission electron microscopy (TEM) were performed at JSM-6510 and JEM-2100HR, respectively. The surface composition of electrode was analyzed by Fourier transform infrared spectroscopy (FTIR) (Bruker Tensor 27, Germany) and Xray photoelectron spectroscopy (XPS, Escalab 250, USA). X-ray diffraction (XRD, Bruker D8 Advance, Germany) was chosen to investigate the structural stability of LNCA. Inductively coupled plasma atomic emission spectrometer (ICP-AES, Optima 8300, USA) was employed to analyze the deposition of the dissolved transition metals on cycled lithium plate. Ionic conductivity of electrolyte was measured by Metrohm 856 instrument. The analyses of aluminum foil corrosion were conducted on metal phase microscope (OPTEC, MDS 15020009). 2.3. Calculation methods Gaussian 09 package was used to carry out theoretical calculations. Geometric structures of the investigated molecular/complex were obtained by optimizing with B3LYP method at 6-311++ G (d) basis set. Solvent effect was considered by introducing polarized continuum model using a permittivity of 20.5. In order to guarantee the obtained optimized geometric structures, frequency analyses were employed. The oxidation potential (Eox) was calculated as our previous works30, 31. 3. Results and discussion 3.1. Oxidation activity of NNB-containing electrolyte SEI film-forming electrolyte additive should possess high oxidation activity to insure its preferential oxidation decomposition, which creates a compact protective film to prevent the subsequent oxidation of baseline electrolyte. Therefore, oxidation


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activity is the key parameter for an effective film-forming electrolyte additive. Figure 1 presents the LSV and CV curves of electrolyte with and without 2 wt. % NNB additive. It can be easily found from Figure 1(a) that on Pt electrode, NNB-containing electrolyte oxidizes at lower potential then that of baseline electrolyte. And most importantly, the preferential oxidation of NNB-containing electrolyte greatly passivates the highly charged electrode surface, which dramatically hindered the subsequent oxidation of electrolyte at high potential. Figure 1(b) shows the CV curves of electrolytes on LNCA electrode. There are three couples of redox peaks corresponding to phase transition processes along with lithium intercalation/deintercalation, including hexagon to monocline (H1 to M, at 3.88 V), monocline to hexagon (M to H2, at 4.02 V) and hexagon to hexagon (H2 to H3, at 4.19 V), respectively

32-36

. Lower onset oxidation

potential can be observed from the initial charging curve of NNB-containing electrolyte comparing with baseline electrolyte, revealing the higher oxidation activity of NNB additive on LNCA surface. Similar result can be also found from the differential capacity curve shown in Figure S1 (see supporting information). It should be mentioned that addition of 2 wt.% NNB additive decreases the ionic conductivity of electrolyte from 11.8 to 10.2 mS·cm-1. However, as shown in Figure 1 (b) and S1, the oxidation peak that corresponding to lithium deintercalation reaction in NNB-containing electrolyte appears at lower potential than that of baseline electrolyte, indicating that the reaction resistance of LNCA/Li cell is decreased instead of increased by addition of NNB additive. This may be ascribed to the greatly enhanced ionic conductivity of SEI film generated by NNB additive, which overcomes the slightly decreased ionic



conductivity of electrolyte. In addition, the ionic conductivity of electrolyte should recover after NNB participating in film-forming reaction. The oxidation activity of NNB is further confirmed by DFT calculations, as shown in Figure 1(c). The highest occupied molecular orbital (HOMO) energy of NNB is clearly higher (less negative) than that of carbonate solvents, which indicates that losing a valence electron of the former is easier than that of the later, resulting in lower onset oxidation potential of NNB in comparison to carbonate solvents. It should be mentioned that the bond length of Si-N bond increases from 1.77 to 1.87 Å after oxidation, which may break to generate N(CH3)3 cation and (CH3)3NSiC3H5 radical. The former cation product would easily interact with the negatively charged oxide on the LNCA surface, while the later product would terminate with other radical to create oligomer protective film. 3.2.Influence of NNB on the cyclic performances of LNCA Figure 2 shows the influence of NNB additive on the cyclic performances of LNCA/Li half-cells. It can be found from Figure 2(a) and (b) that application of NNB additive improves the capacity retention of LNCA/Li cell. Specifically, after 300 cycles, the capacity retention of LNCA/Li cell is increased from 72.8% to 89.0%, 91.9% and 90.5% with addition of 1 wt. %, 2 wt. % and 5 wt. % NNB additives, respectively. It is obvious that the cyclic stability of LNCA/Li cell with 2 wt. % NNB is slightly higher than the other two NNB-containing electrolytes. As presented in Figure 2(c), in the 1st cycles, the LNCA/Li cell with 2 wt. % NNB additive shows lower coulombic efficiency than that baseline electrolyte, which should be ascribed to the oxidation and SEI film


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generation of NNB additive. It can be found that the subsequent coulombic efficiency of NNB-containing electrolyte becomes slightly higher and more stable than the one without NNB, indicating the capability of NNB on enhancing the interfacial stability of LNCA/electrolyte via film-forming reaction. It is worth mentioning that the initial coulombic efficiency of LNCA/Li cell with 1 wt. %, 2 wt. % and 5 wt. % NNB additives is 79.5%, 80.2% and 81.2%, respectively, indicating that the content of NNB participates in film-forming reaction decrease as 5 wt.% > 2 wt. % > 1 wt. %. This reveals that the inferior cyclic stability of LNCA/Li cell with 1 wt.% NNB should be ascribed to its insufficient content of NNB to create an integrality condense SEI film. While the worse stability of LNCA/Li cell with 5 wt.% NNB in comparison with that of 2 wt. % NNB should be due to the excess film-forming reaction, which results in thicker SEI film and lower initial discharge capacity, see Figure 1 (a). And therefore, electrolyte with 2 wt. % NNB was chosen for further investigations. Figure 2(d) and (e) present the selected charging/discharging curves of LNCA/Li cells during cycling at 1 C rate. It can be found that the charging/discharging voltage platform of LNCA/Li cell with baseline electrolyte increase/decreases continuously, revealing the increases of electrode polarization during cycling. Deposition of electrolyte decomposition products and damage of the electron conducting network of LNCA are the major cause of the increased electrode polarization. Application of NNB additive effectively suppresses the electrode polarization of LNCA during cycling, which result in improved rate capability of LNCA/Li. Indeed, as shown in Figure 2(f), at higher discharge rate, such as 3 C, 5 C and 7 C, the LNCA/Li cell with NNB additive



exhibits higher discharge capacity than that of baseline electrolyte. EIS result of the LNCA/Li cells after different cycles are given in Figure 3, together with the equivalent circuit diagram. It is obvious that the EIS curves mainly contain two depressed semicircles at high and medium frequency and a diagonal line at low frequency. It has been well accepted that the depressed semi-circle reveals the reaction resistance of surface film (Rfilm) and charge transfer (Rct), and the slope line reflects the Warburg impedance. The fitting line generated from the equivalent circuit shows high consistency with the EIS spectra, with the corresponding fitting data shown in Figure 3(e) and (f). The EIS results demonstrate that in baseline electrolyte, the interfacial resistance of LNCA/Li cell increases significantly during cycling, especially Rfilm, which should be mainly derived from the decomposition and deposition of baseline electrolyte. It can be found from Figure 3 that the interfacial resistance of LNCA/Li with NNB additive is always lower than that of electrolyte without additive, which well explains the superior rate capability of the former. The lower interfacial resistance of LNCA/Li cell with NNB additive further confirms the great capability of NNB-derived SEI film on improving the interfacial stability of LNCA/electrolyte. 3.3 Influence of NNB on the interfacial composition and morphology of LNCA Figure 4 presents the SEM and TEM images of LNCA before and after cycling. Polymer film products covering on the surface of cycled LNCA can be easily identified, which is due to the electrolyte oxidation decomposition. The NNB-derived film is more uniform and thinner than that of baseline electrolyte, confirming that application of NNB additive greatly hinders the continuous electrolyte decomposition. Besides the


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surface film, the morphology of LNCA electrode maintains well after cycling with NNB additive, indicating that the generated SEI film could also improve the structural stability of LNCA. While after cycling in electrolyte without NNB, irregular cracks can be observed on the LNCA surface, suggesting the breakdown of the electronic conduction network, which is in good agreement with the increase of Rct of LNCA/Li cell cycling in baseline electrolyte (see Figure 3). The higher structural stability of LNCA cycling in NNB-containing electrolyte can be also found from the XRD patterns given in Figure 5 (a). After 300 cycles, the peak intensity of LNCA electrode with baseline electrolyte is clearly weaker than that of NNB-containing electrolyte. Additionally, I003/I104 ratio of LNCA after cycling in baseline electrolyte (I003/I104= 0.144) is lower than in NNB-containing electrolyte (I003/I104= 0.667), revealing that Li+/Ni2+ disorder of the former is more serious than that of the later 34, 37. Figure 5 (b) shows the deposition content of Ni and Al on Li plate, which would reflect the transition metal dissolution of LNCA and corrosion of Al current collector during cycling. The deposition content of Ni and Al on lithium plate after cycling with NNB additive is lower than with baseline electrolyte, further revealing the capability of NNB on hindering the structural deterioration of LNCA. The higher deposition content of Al in comparison with Ni is due to the corrosion reaction of Al current collector, which may result from the increased HF content during cycling. The morphology of Al current collector before and after cycling can be found in Figure S2. It should be mentioned that the content of Co is lower than the detection limit of ICP-AES, which may be due to its lower stoichiometry in LNCA and negligible



dissolution. XPS is used to analyze the surface composition of LNCA electrode after cycling, as presented in the Figure 6. The C 1s spectra of LNCA after cycling mainly contains C from PvdF and C=O, C-O, C-C from electrolyte decomposition products. Peaks corresponding to C-N and Si-C can be only found from the one cycling with NNB additive, revealing the participation of NNB in the film-forming reaction. Decomposition reaction of NNB additive can be also identified from the appearance of C-N, Si-N peaks and Si-C, Si-N peaks of N1s and Si 2p spectra, respectively 38, 39. The O 1s spectra of LNCA after cycling in baseline electrolyte is similar to that of NNBcontaining electrolyte, except that the peak intensity of the later is lower than that of the former, confirming the capability of NNB on suppressing electrolyte decomposition. It can be noted that the intensity of PvdF in C 1s is slightly higher than that of NNBcontaining electrolyte, and the intensity of M-O in O 1s is similar for two electrodes. This result is mainly because of the non-uniform electrolyte decomposition products deposited on the LNCA surface, as shown in Figure S3. The thinnest deposition product is around 10 nm which is similar with that of NNB-containing electrolyte, see Figure 4 (i). The LixPOyFz, LiF from F 1s spectra and LixPFy and LixPOyFz from P 2p reveal the co-oxidation of LiPF6 during the decomposition of electrolyte. Therefore, the lower peak intensity of F 1s and P 2p spectra from LNCA after cycling with NNB additive again indicates the passivation capability of NNB-derived SEI film. Film-forming reaction of NNB additive was also confirmed by the FTIR characterization displayed in Figure S4 (see supporting information).


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The Ni 2p, Co 2p and Al 2p spectra of LNCA are given in Figure 7 (a), (b) and (c), respectively. It can be found that the Ni 2p, Co 2p and Al 2p peak intensity of LNCA after cycling in baseline electrolyte decreases dramatically, while the one cycling with NNB additive maintains very well. The decreased intensity of these transitions metal of LNCA after cycling in baseline electrolyte is due to the generated thick surface film and the serious metal dissolution, see Figure 3(e) and 4(f). Detailed information of Ni 2p spectra is presented in Figure 7(d), (e) and (f). It has been proved that the decreased ratio of Ni2+/(Ni2++Ni3+) can be ascribed to the increase of Li+/Ni2+ disorder of Ni-rich electrode,33, 40 which leads to structural breakage and capacity fading. The ratio of Ni2+/(Ni2++Ni3+) of LNCA before and after cycling in electrolytes with and without NNB is 38%, 37% and 31%, respectively, indicating that the Li+/Ni2+ disorder of the LNCA cycling in baseline electrolyte is worse than that of NNB-containing electrolyte, which in line with the XRD results presented in Figure 5. 3.4 Influence of NNB on the cyclic stability of graphite/Li and LNCA/graphite cells Influence of NNB additive on the cyclic performances of graphite/Li half-cell and LNCA/graphite full-cell were also investigated, as shown in Figure 8. It can be found that the 1st and 2nd charging/discharging curves of graphite/Li half-cell with and without NNB additive is similar. As shown in Figure 8 (a) and (b), a short reduction potential platform in the initial charging process (lithium de-insertion) is ascribed to the SEI generation of EC-based electrolyte, leading to a lower coulombic efficiency of the 1st cycle comparing with the subsequent cycles, see Figure 8 (d). Moreover, according to Figure 8 (c), it can be easily found that NNB additive shows negligible effect on the



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cyclic stability of graphite/Li half-cell. Cyclic stability of LNCA/graphite full-cells with and without NNB were shown in Figure 8 (e) and (f). The capacity retention of full-cells after 100 cycles was improved from 40% to 61% with 2 wt.% NNB addition, which is obviously benefited from the great capability of NNB on improving the interfacial stability of LNCA cathode.

Conclusions The development and application of Ni-rich LNCA is subject to its poor cyclic stability caused by its interfacial instability. The incessant electrolyte oxidation on the LNCA surface results in increasing interfacial reaction resistance. Moreover, the interfacial side reaction also leads to dissolution of transition metal ions and Li+/Ni2+ disorder of LNCA, which further aggravates the capacity fading of LNCA. In this work, we demonstrate that application of a high oxidation activity and great film-forming capability

additive,

N-Allyl-N,N-bis(trimethylsilyl)amine

(NNB),

significantly

improves the cyclic stability of LNCA. The capacity retention of LNCA/Li half-cell is improved from 72.8% to 86.2% after 300 cycles via addition of 2 wt. % NNB into the electrolyte. Characterization results of the interfacial composition and morphology show that NNB creates a thin and uniform SEI film on the LNCA, and importantly, effectively suppress the subsequent electrolyte oxidation and structural breakage of LNCA. Charging/discharging tests reveals that NNB effectively improve the cyclic stability of LNCA/graphite full-cell, which is obviously benefited from the great capability of NNB on improving the interfacial stability of LNCA cathode.


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Supporting Information: Differential charge capacity curves of LNCA/Li half-cells, morphology of Al current collector after cycling in LNCA/Li half-cell, additional SEM and TEM images of LNCA after cycling in baseline electrolyte, and FTIR spectra of LNCA electrodes after cycling were supplied as Supporting Information. Acknowledgments This work is supported by the National Natural Science Foundation of China (21573080), the Pearl River S & T Nova Program of Guangzhou (201506010007), Guangdong Program for Support of Top-notch Young Professionals (2015TQ01N870) and Distinguished Young Scholar (2017B030306013), and the Science and Technology Project of Administration of Quality and Technology Supervision of Guangzhou Municipality (2015kj34). References: (1) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-ion Battery Materials: Present and Future. Mater. Today 2015, 18, 252-264. (2) Myung, S. T.; Maglia, F.; Park, K. J.; Yoon, C. S.; Lamp, P.; Kim, S. J.; Sun, Y. K. Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives. ACS Energy Lett. 2017, 2, 196-223. (3) Martha, S. k.; Haik, O.; Zinigrad, E.; Exnar, I.; Drezen, T.; Miners, J. H.; Aurbacha, D. On the Thermal Stability of Olivine Cathode Materials for Lithium-Ion Batteries. J. Electrochem. Soc. 2011, 158, A1115-A1122. (4) Etacheri, V.; Marom, R.; Elazari, R.; Salitra, G.; Aurbach, D. Challenges in the Development of Advanced Li-Ion Batteries: A Review. Energy Environ. Sci. 2011, 4, 3243-3262. (5) Makimura, Y.; Sasaki, T.; Nonaka, T.; Nishimura, Y. F.; Uyama, T.; Okuda, C.; Itou, Y.; Takeuchi, Y. Factors Affecting Cycling Life of LiNi0.8Co0.15Al0.05O2 for Lithium-Ion Batteries. J. Mater. Chem. A 2016, 4, 8350-8358.



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Figure captions: Figure 1. LSV profiles of Pt electrode with baseline and NNB-containing electrolytes

(a); CV curves of LNCA/ Li cells with baseline and NNB-containing electrolytes (b); optimized structures and the corresponding calculated oxidation potential (V vs Li+/Li) and highest occupied molecular orbital (HOMO) energy of NNB, EC, EMC, and DEC (c). Figure 2. Cyclic stability (a), capacity retention (b), coulombic efficiency (c), selected charging/discharging curves (d and e) and rate capability (f) of LNCA/Li cells cycled in baseline and NNB-containing electrolytes. Figure 3. EIS of LNCA/Li cells after 2 (a), 200 (b) and 300 (c) cycles in electrolytes with and without 2 wt % NNB additive; equivalent circuit diagram (d) and the corresponding fitting data (e and f). Figure 4. SEM and TEM images of LNCA electrodes before (a, b and c) and after 300 cycles in electrolytes without (d, e and f) and with 2 wt % NNB additive (g, h and i). Figure 5. XRD patterns of LNCA electrodes before and after cycling (a); deposition content of Ni and Al on the counter lithium electrodes after 300 cycles (b). Figure 6. XPS spectra of C 1s, O 1s, F 1s, P 2p, N 1S and Si 2p of LNCA electrodes after 300 cycles. Figure 7. XPS spectra of Ni 2p, Co 2p, Al 2p (a, b, c) and fitting results of Ni 2p spectra (d, e, f) of LNCA electrodes after 300 cycles. Figure 8. First and second charging/discharging curves of graphite/Li cells in electrolytes without (a) and with (b) 2 wt % NNB additive; cyclic stability (c) and coulombic efficiency (d) of graphite/Li cells in electrolytes with and without 2 wt % NNB additive, cyclic stability (e) and coulombic efficiency (f) of LNCA/graphite fullcells in electrolytes with and without 2 wt % NNB additive.



Figure 1. LSV profiles of Pt electrode with baseline and NNB-containing electrolytes

(a); CV curves of LNCA/ Li cells with baseline and NNB-containing electrolytes (b); optimized structures and the corresponding calculated oxidation potential (V vs Li+/Li) and highest occupied molecular orbital (HOMO) energy of NNB, EC, EMC, and DEC (c).


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Figure 2. Cyclic stability (a), capacity retention (b), coulombic efficiency (c), selected charging/discharging curves (d and e) and rate capability (f) of LNCA/Li cells cycled in baseline and NNB-containing electrolytes.



Figure 3. EIS of LNCA/Li cells after 2 (a), 200 (b) and 300 (c) cycles in electrolytes with and without 2 wt % NNB additive; equivalent circuit diagram (d) and the corresponding fitting data (e and f).


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Figure 4. SEM and TEM images of LNCA electrodes before (a, b and c) and after 300 cycles in electrolytes without (d, e and f) and with 2 wt % NNB additive (g, h and i).

Figure 5. XRD patterns of LNCA electrodes before and after cycling (a); deposition content of Ni and Al on the counter lithium electrodes after 300 cycles (b).



Figure 6. XPS spectra of C 1s, O 1s, F 1s, P 2p, N 1S and Si 2p of LNCA electrodes after 300 cycles.


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Figure 7. XPS spectra of Ni 2p, Co 2p, Al 2p (a, b, c) and fitting results of Ni 2p spectra (d, e, f) of LNCA electrodes after 300 cycles.



Figure 8. First and second charging/discharging curves of graphite/Li cells in electrolytes without (a) and with (b) 2 wt % NNB additive; cyclic stability (c) and coulombic efficiency (d) of graphite/Li cells in electrolytes with and without 2 wt % NNB additive, cyclic stability (e) and coulombic efficiency (f) of LNCA/graphite fullcells in electrolytes with and without 2 wt % NNB additive.


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N-Allyl-N,N-Bis(trimethylsilyl)amine as a Novel Electrolyte Additive to

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