Enhanced Capacity of NiO Nanocubes with High Dispersion and

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Letter

Enhanced Capacity of NiO Nanocubes with High Dispersion and Exposed Facet Reinforced by Thermal Plasma Guolin Hou, Yu Du, Benli Cheng, Yijun Yang, Daliang Fang, Xiang-Peng Kong, Baoqiang Li, Jiaping He, Jiawei Yang, Xi Wang, and Fangli Yuan ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01398 • Publication Date (Web): 08 Nov 2018 Downloaded from http://pubs.acs.org on November 13, 2018

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ACS Applied Nano Materials

Enhanced Capacity of NiO Nanocubes with High Dispersion and Exposed Facet Reinforced by Thermal Plasma Guolin Hou a, Yu Du a,b, Benli Cheng a, Yijun Yang c, Daliang Fang a,b, Xiangpeng Kong d, Baoqiang Li a,b, Jiaping He a, Jiawei Yang a, Xi Wang c, * and Fangli Yuan a,* a

State Key Laboratory of Multi-phase Complex Systems, Institute of Process

Engineering, Chinese Academy of Sciences (CAS), Zhongguancun Beiertiao 1 Hao, Beijing 100190, China b

University of Chinese Academy of Sciences (UCAS), No.19A Yuquan Road, Beijing

100049, China c

d

School of Sciences, Beijing Jiaotong University, Beijing, 100044, China College of Chemistry and Chemical Engineering, Jiangxi Normal University,

Nanchang 330022, China

Corresponding Authors *E-mail: [email protected]; Fax: +86-10-62561822; Tel: +86-10-82544974 *E-mail: [email protected]. or Wang. [email protected].

ABSTRACT Structure architectonics have great effect on the electrochemical performance for conversion mechanism materials, as they face inevitable big volume changes and serious agglomeration during the lithiation/delithiation process, subsequent with particle crack and electrode pulverization. Here, we report a simple method for the scalable preparation of ultra-fine NiO nanocubes (~500 g/h) with high dispersion and exposed crystal facets reinforced by thermal plasma. In-situ transmission electron 1

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microscopy (TEM) observation and density function theory (DFT) calculation reveal that: NiO nanocube could not only enable stable morphology and small volume expansion (56%) at fully lithiated, but also facilitate lithium ion transportation. These characteristics result in improved cycling performance and enhanced rate capability. More importantly, during the lithiation process, ultrafine Ni particles were formed. The Ni particles may catalyze the decomposition of inreversible Li ion in the solid electrolyte interlayer (SEI) and lead to the capacity increased. Using as LIB anodes, the as-synthesized NiO nanocubes show an impressive electrochemical performance: high capacity for long cycle (>1000 mA h g−1; 600 cycles), improved coulombic efficiency (CE; >99%) and superior rate property. This work provides a visualized result for exploring the atomic-scale structure evolution of NiO during the lithiation process, and is hoped to be a guide for developing advanced conversion mechanism materials with higher performance. KEYWORDS: RF plasma; NiO; Nanocubes; Anode; Li-ion batteries

INTRODUCTION Lithium-ion batteries (LIBs) are considered as one of the most powerful energy storage systems and widely used in consumer electronics and electric/hybrid Vehicles12

. With the ever-increasing demand for energy densities, high-performance LIBs with

enhanced power densities and improved cycle stability are in urgent needed3-4. Commercial graphite anodes are approaching their theoretical capacity, and the improvement of capacity is limit5-6. Conversion mechanism materials, e.g. transition metal oxides (TMO), are considered as promising anode materials for advanced LIBs 2


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because of the high theoretical capacity7-10. Specially, NiO is proposed as one interesting anode material, owing to the comparatively high capacity (718mAh g-1), low cost, eco-friendliness, natural abundance and more importantly, high volumetric energy density (6.67 g cm-3, approximately 5.8 times of graphite)11-14. Nevertheless, the properties of NiO have been restricted by the large volume change (100%) and severe particle aggregation, which leads to cycling instability and capacity fading during the repeated lithium uptake/release process15-17. Nanostructured TMO are believed could resolve these disadvantages, due to the short diffusion lengths, high reactivity and good stress accommodation18-22. Variety of nano-structured NiO were manufactured and obtained good performance23-27. For example, Schmidt and co-workers28 prepared NiO nanomembranes through a rolled-up process and thermal oxidation. The NiO nanomembranes showed satisfied performance with super power rate, high capacity of ~720 mA h g-1 over long cycles. Ozkan et al.29 fabricated NiO nanowires with solution synthesis and hydrogen reduction. The NiO nanowires demonstrate good rate capability, high capacity of 680 mA h g−1 over 1000 cycles. Despite the improvements, the serious agglomeration problem for NiO nanoparticles is still unresolved. The agglomeration would lead to larger volume expansion and more capacity decay during cycling30. For example, for an aggregated NiO nanosheet31, it exhibited an initial capacity of >1000 mA h g-1 at the 1st cycle. But, because of the serious aggregation, the capacity quickly dropped to 770 mA h g-1 in the 2nd cycle and sharply decayed in the following cycles. After 50 cycles, less than 150 3



mA h g-1 was retained. Therefore, except for the capacity lost deriving from the formation of SEI, the serious agglomeration problem for nanoparticles has become the key point of restricting their further application in LIBs. However, the preparation of highly dispersed NiO nanostructures by traditional methods still faces great challenge. Moreover, it is important but still difficult to achieve the scalable manufacturing of nanostructures because of the complex synthesis processes32. On the other hand, structure architectonics e.g. exposed facets also have great effect on the electrochemical properties for conversion mechanism materials10, 33-34. Material with high-efficient exposed facets have more open channels for Li+ transportation. Su et al.35 found that it is easier for Li-ion to transport along for NiO, there more open channels are effective for Li+ diffusion. Jin et al.36 found that high exposure of {111} facets of NiO can effectively improve the Li ion diffusion and accelerate the conversion reaction kinetics. Designing advanced NiO with controllable structures relies on the deep understand of structural evolution behaviors during the lithiation process. However, there is still rarely studies providing an atomic-scale analysis of the structural evolution of NiO. In this work, NiO nanocubes were synthesized in batches through thermal plasma in a single step. Thermal plasma has ultra-high reaction temperature (104 K)37-38, rapid cooling rate (105-106 K s-1) and continuous operation, which makes it possible for NiO to form crystal nucleus at high-temperature region and grow into nanocubes at lowtemperature region (Fig. 1). This process has been demonstrated to produce 500 g/h NiO nanocubes using bulk-Ni as raw material and has successfully accomplished 4


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dozens of kilograms. The as-synthesized NiO nanocubes have many advantages in applicating in LIBs anode: (1) continuously and batch production quantity (~500g/h) with well dispersed nano-sized particles; (2) special nanocube morphology with short diffusion distance and high exposed crystal facets of (111) and (220) to facilitate the lithium ion and electronic transfer; (3) accommodation small volume expansion of 56%, enable a stable and thin SEI layer to maintain particle integrity; (4) ultrafine Ni particles/clusters formed during the lithiation process activate the irreversible Li ion in the SEI, resulting in enhanced capacity of >1000 mA h g−1 and long cycling stability.

Figure 1 Schematic of the synthesis process of NiO nanocubes by plasma.

RESULTS AND DISCUSSION The powder prepared by thermal plasma was firstly characterized in detail to detect the morphology and structure. As shown in Figure 2a, all peaks in the diffraction spectrum of the powders are consistent with the standard diagram of NiO (JCPDS card No.00-048-1576). The sharp diffraction peaks indicate that high crystallization NiO was obtained. Raman spectrum was further conducted and shown in Figure S2 (Supporting Information, SI), there are five typical broad peaks centered at 488, 728, 5



910, 1095 and 1440 cm−1. They are the first-order transverse optical mode (TO), longitudinal optical (LO), 2TO, 2LO and a strongest two magnon scattering (2M) band at around 1440 cm-1, respectively39-40. Figure 2b-c display the morphology of the NiO nanocubes. As can be observed, the nanocubes with 50-100 nm are dominant in assynthesized products. Moreover, most nanocubes possess smooth surface and welldispersion, owing to the plasma reinforce with ultra-high reaction temperatureand steep cooling rate41. Figure 2d exhibits clear lattice stripes, indicating that the as-prepared nanocubes have perfect single crystalline structure. The lattice spacing measured to be 0.24 nm is belonging to (111) facet of NiO, while the 0.15 nm is corresponding to (220) facet. Combined with the electron diffraction (Fig. 2d inset), it indicates that NiO nanocubes with high exposed crystal facets were synthesized.

Figure 2 (a) XRD pattern of the as-synthesized products; (b-c) SEM and TEM of NiO nanocubes; (d) HRTEM and the SAED (inset) of single NiO nanocube; XPS spectra of NiO nanocubes composite: (e) Ni 2p, (f) O 1 s. X-ray photoelectron spectroscopy (XPS) was further conducted to detected the 6


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surface chemical states of the NiO nanocubes. According to the full range of the XPS spectra in Figure S3, NiO nanocubes are composited of Ni, O and C elements, while the C is mainly from the contamination during the test. In the high-resolution spectrum of Ni 2p shown in Fig.2e, there are two regions attributed to the spin-orbit levels of Ni 2p1/2 (870-885 eV) and Ni 2p3/2 (850-865 eV), respectively. Figure 2f shows the O 1s spectrum and there are three oxygen contributions. Specifically, the peak located at 529.6 eV is owing to the Ni-O bonding structure42, while the peak at 531.6 eV is generally ascribed to oxygen in OH- groups43. Furthermore, the peak at 533 eV is assigned to the physi/chemisorbed H2O on the surface of NiO nanocubes, which confirms the large surface area of as-prepared NiO nanocubes44. All these results confirm that well-defined NiO nanocubes were successfully synthesized in one-step and large-scale. With short diffusion distance and high exposed crystal surface, the special NiO nanocube is expected to possess good electrochemical performance.

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Figure 3. The electrochemical properties of NiO nanocubes: (a) cyclic voltammetry profiles of the first three cycles in 0.01-3.0 V scanned at 0.1 mV s-1; (b) Dis-/charge voltage profiles of NiO electrodes at 0.2 C; (c) Long cycle performance at 0.2 C and (d) Rate performance of NiO nanocubes at various current densities (0.1 C to 1 C). It is vital for NiO nanocubes to have suitable electrochemical performances including improved capacity, long cycling life (>500 cycles) and super rate capability. Here, NiO nanocubes were systematically estimated by assembled into a CR2025 half coin-cell. To study the inherent properties of NiO nanocubes, cyclic voltammetry (CV) were firstly conducted, which could directly reflect the electrochemical reactions characteristics. As displayed in Figure 3a, during the 1st cycle, the sharp peak at 0.5 V in the cathodic curve is ascribed to the SEI formation and NiO reduction (NiO+2Li++2e→Li2O+Ni)45. At the subsequent cueves, this peak weakens and shifts to 1.25 V. The phenomenon is thought to be attributed to the structural/textural modifications driven 8


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by Li+ insertion12. In the anodic curve, the broad peak located at 2.10~2.25 V is attributed to the Li2O decomposition and Ni oxidation (Ni + Li2O→NiO + 2Li+ + 2e−)45. It is worth mentioning that, after the second cycle, the CV curves become similar, demonstrating that the NiO electrode has super capacity reversibility and retention. The discharge-charge voltage curves of the NiO electrodes after various cycles were conducted at 0.2 C within 0.01-3.0 V. As shown in Figure 3b, in the 1st discharge curve, the NiO electrode displays a long potential plateau at about 0.6 V. And during the subsequent cycles, this plateau is instead by a sloping curve from 1.5 to 0.9 V voltage. The result is in well agreement with the CV data. During the 1st cycle, there is a large capacity loss, which is attributed to the irreversible formation of solid electrolyte inter layer. This is a common feature for most metal oxide material anodes46. Note that, after the 2nd cycle, the capacity of NiO keeps increasing and the Coulombic efficiency (CE) also gradually increases up to > 99.0%. High CE also confirms the stability of the SEI on NiO surfaces47. Cycle life is thought to be a key performance characteristic for many Li-ion batteries, especially for LIBs used in portable devices. Thus, the long-term cycling performance of NiO was tested and demonstrated in Fig. 3c. The capacity of the electrodes holds steady of ~700 mAhg-1 after the 2nd cycle, and increases up to ~1200 mA h g−1 after 300 cycles. Even after 600 cycles, the capacity still keeps >1000 mA h g−1, which is about three times the theoretical capacity of commercial graphite. We also made a comparation with the previously reported NiO nanomaterials with various morphologies. As shown in Table S2 in the supporting information, compared with the 9



reported NiO materials, the prepared NiO nanocubes manifest ultrahigh capability and superior cycling stability. In general, the increased capacity higher than theoretical value is believed to due to the electric double layer capacity and the activated process in nanocubes48. Actually, the formation/decomposition of solid electrolyte interlayer promoted by the Ni nanoparticles (generated in the charging/discharging), also accounts for the increased capacity49-50. This would be described in detail in the following in situ TEM analysis. Rate performance is considered as one of the important properties, especially for LIBs used in high power device, e.g. electric vehicles. Thus, the rate performance of NiO nanocubes was systematically estimated at various current densities. As shown in Figure 3d, at the current densities of 0.1 C, 0.2 C and 0.5 C, the NiO exhibits a discharge capacity are 620, 590 and 530 mA h g−1, respectively. Note that even at a larger current of 1.0 C, the capacity is still as high as 475 mA h g-1. More importantly, as the current is reduced to 0.1 C, the reversible capacity quickly raises to its initial value. The superior rate performance further suggests that the NiO nanocubes could maintain structure stable even at high current density. These remarkable electrochemical performances of NiO nanocubes are thought to be owing to the short diffusion distance and high exposed crystal facets.

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Figure 4 In situ TEM observations of the NiO nanocubes during lithiation process. a, Illustration of the nano-scaled battery setup. b, TEM images of signal NiO nanocube before lithiation and lithiated for 15 s, 30 s and 35 s, respectively. c, Schematic illustration of the lithiation process and (d) the volume changes for lithiation along the , and directions. HRTEM images of NiO nanocube before lithiation (e) and after lithiation (f-g), and the corresponding SAED pattern (h) and (i), respectively. j, FTIR spectrum of NiO nanocube after cycle 50 and 300. k, The crystal structure of the , and of c-NiO when a Li atom inserts. l, Formation energy of LixNiO for Li atoms inserting in NiO crystal along the directions of , and . m, Schematic explaining anisotropic expansion of NiO nanocube. The special microstructure of NiO nanocube is believed to be the key point in its electrochemical enhancements. However, there is still rarely atomic-scale observation of the microstructure changes of NiO during the lithiation process. Thus, a nano-scaled 11



battery was conducted utilizing in-situ TEM technique51-52. This nano-scaled battery consists of several NiO nanocubes and a piece of metallic lithium and is schematically illustrated in Figure 4a. In the nano-scaled battery, NiO nanocubes are the working electrode and adhered to an Au wire, while the Li metal is the counter electrode and adhered to the opposite W wire. On the surface of Li metal, there is a naturally oxidized lithium oxide layer, which is served as solid electrolyte. Figure 4b and Supplementary Video 1 show the structure and volume changes of NiO nanocube during the lithiation processing. The lithiation reaction took place quickly as a -2 V voltage was added between the NiO and lithium metal. The lithiation started from one edge of the NiO nanocube and moved inward gradually to the other side along the direction of Li-ion diffusion, until the darker core finally disappeared. At the same time, large amounts of nanograins were generated at the reaction site. Figure 4c illustrates the lithiation process and the volume changes. Note that, for a NiO nanocube with an initial particle size of ~90 nm, after fully lithiated in 35 s, it expanded to ~105 nm, resulting in a volume change of 56%. This value is much smaller than the previously reported volume change (~100%). An ab initio density functional theory (DFT) calculation in Fig. 4d and Fig.S4 (SI) reveal that Li+ diffusion along direction undergoes much less volume expansion (87%) than that of (104%) and direction (110%). Thus, the high exposed (111) facet of NiO nanocubes could enable much smaller volume expansion. Such features are very advantageous for achieving excellent performance in volume change-sensitive Li-ion cells. Importantly, after lithiation, a 6 nm-thin SEI/Li2O layer (Figure 4f) was found on 12


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the NiO surface and exhibited no obvious increase during the following lithiation, indicating a stable and thin SEI layer. The result well agrees with the ultra-high CE of ~99% after cycles. Moreover, after lithiation, numerous ultrafine Ni nanograins (dark spots, marked by red circles) with size of 1~2 nm generated (NiO+2Li++2e-→Li2O+Ni) and connected into network in the Li2O matrix. The conversion reaction can be further demonstrated by the phase transition shown in SAED images. As shown in Fig.4h-i, after lithiation, the diffraction spots of c-NiO became weaker and finally changed to typical Li2O arcs and Ni diffraction spots. This indicates that the NiO is almost totally converted to Ni nanograins and Li2O matrix17. Importantly, after several in situ lithiation/delithiation process, the SEI/Li2O layer thinned to 3.6 nm from 6.0 nm as shown in Fig.4g. The FTIR spectrum of the electrodes in Figure 4j also demonstrates that the corresponding Li-C bond became weaken from cycle 50 to cycle 300. This suggests that Ni particles/clusters formed during the lithiation process may function as effective catalyst and activate the irreversible Li ion in the SEI49. Thus, these generated Ni nanograins play important role in the available Li ion and capacity increase. This is well consistent with the enhanced cycle capacity in Fig.3c. Also, the Ni/Li2O network provides facile conductive path for the transportation of Li+ and electrons, thus ensuring super rate performance53. Interestingly, during the in situ TEM lithiation, an amazing phenomenon was observed: NiO nanocubes favor to turn into tori-spheres after lithiated rather than expanded nanocubes (as shown in Fig.4b1→b4). This was thought to be related to the volume expansion directions priority during the lithiation processes. Figure 4k shows 13



the crystal structure of c-NiO viewed along the , and for a Li atom insertion. As exhibited in Figure 4k, the interstitial spaces between atoms along the direction are obvious larger than those along and . That is, the direction could supply much larger ion channels for Li-ion insertion during the lithiation processe54, and it is expected to have the lowest energy barrier for lithiation. Then, the formation energy of LixNiO at different lithium amounts lithiated along the, and directions were further calculated using ab initio density functional theory (DFT). Details about the theoretical calculations were described in SI. As expected in Figure 4l, the formation energies for lithiation along the directions are the lowest, indicating that Li+ transports more easily along directions31. Thus, during the lithiation, Li+ prefers to diffuse into the NiO crystal along the directions and starts the lithiation reaction at the (110) facets, where the lithium is preferentially concentrated. For cubic system, there are four directions in the axially oriented nanocube, as shown in Fig. 4m. As the lithiation proceeded, Li2O matrix and Ni nanograins were generated and pushed the crystalline NiO core away along the directions, resulting in the nanocube expanding into a tori-sphere. This special structural evolution mechanisms could effectively accommodate the volume change stress and prevent the particle from cracking during lithiation. This finding provides a visualized data for exploring the atomic-scale structure evolution of NiO during the lithiation process, which is hoped to provide inspiration for the development of advanced NiO anodes with higher performance.

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Figure 5. (a-b) Ex situ morphology changes of NiO nanocube anode before and after cycles. (c-d) Cross-sectional SEM images of NiO electrodes before and after cycles. (e) Electrochemical impedance spectra (EIS) of NiO half-cell before and after cycles, and (f) the illustration of the Li storage mechanism of NiO nanocubes. The mechanism during electrochemical lithiation could also be illustrated by the ex-situ structural evolution of NiO electrode before and after cycling. As displayed in Figure 5a-b, after cycling, most of the original NiO nanocubes in the electrode turned into tori-spheres. The NiO nanocubes exhibit a slightly volume changes after cycles with SEI layer coated on the surface, but still contact closely on the Cu foil, which is beneficial to maintain the electrode framework stable. The cross-sectional SEM images of the electrode before and after cycles also prove this conclusion. As shown in Figure 5c-d, after cycles, the electrode is still tiled tightly on the Cu foil, with only a small thickness increase (7.5 μm→10.2 μm). Electrochemical impedance spectroscopy (EIS) 15



can also reflect the electrode electrochemical/physical evolution during the cycle process. Figure 5e is the electrochemical impedance spectroscopy of NiO electrode before and after cycles. All Nyquist plot curves show a semicircle and an inclined line. In high-frequency, the intercept reflects the resistance of electronic (Re), and the diameter of the semicircle reflects the resistance of charge transfer (Rct). In low frequency, the incline line represents the impedance of Warburg (Zw), reflecting the Li+ diffusion resistance in electrode55. According to the inset electrical equivalent circuit, the small semicircle diameter before cycling indicates relatively small resistance Rct (80.5 Ω) at the interface between electrode and solution. For the subsequent plot, the Rct increases a little (cycle 2→100.2 Ω; cycle 5→102.3 Ω) due to the SEI layer formation. However, after 400 cycles, the Rct (30 Ω) decreases significantly and even much smaller than that of the electrode before cycling. The dramatic reduction of Rct again confirms the electrochemical activation by Ni nanograins and the conductive path supplied by Ni network56. The results also well explain the improvement of reaction kinetics and the increasement of capacity. In conclusion, the enhanced capacity and superior rate property could be contributed to the interesting nanocube structure. As illustrated in Figure 5f, the ultrasmall NiO nanocube with high dispersion and exposed crystal facets, can significantly decrease the volume expansion and promote the Li+ transfer during the Li insertion/extraction processes. Moreover, the special spheroidization structural evolution mechanism could relieve the volume expansion stress and keep the NiO particle integrity. Also, the generated ultra-fine Ni nanograins play important role in 16


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the capacity increasement, as they can catalyze/accelerate the electrochemical reaction. Thus, the unique nanocube structure and special spheroidization structural evolution mechanism could effectively restrain the volume change and keep the structure stable, leading to superior electrochemical performances.

CONCLUSION In summary, NiO nanocubes with high dispersion and exposed facet were successfully fabricated in batches through a single step reinforced by thermal plasma. These nanostructured NiO exhibit impressive results with increased capacity of 1000 mA h g−1, high coulombic efficiency of 99% and improved rate capability. In situ HRTEM and DFT calculation unveil a small volume variation (~56%), stable and thin SEI layer and fast lithium ion transportation. Importantly, ultrafine Ni particles/clusters formed during the lithiation process could activate the irreversible Li ion in the SEI, resulting in increased capacity. These results provide a comprehensive data for exploring the atomic-scale structure evolution of NiO during the lithiation process. We envisage that our work can be a guide for developing advanced conversion mechanism materials with higher performance.

EXPERIMENTAL SECTION Materials synthesis The detailed NiO nanocube synthesis process is demonstrated in Figure 1. NiO nanocubes were continuously fabricated in batches through a-single-step reinforced by thermal plasma. Detail configuration of the apparatus is available in Figure S1 (Supporting Information) and our previously reported works38. In this method, we use 17



irregular bulk metal Ni (30-50 μm) as the raw material, which was transported in the plasma by a carrier gas (O2, 99.9%). The metal Ni evaporated in the plasma jet and formed NiO crystal nucleus with O2, then grew up into NiO nanocubes in the low temperature zone. After reaction, a large amout of yellow-green samples were deposited in the collector. The powder prepared by thermal plasma was characterized in detail to detect the morphology and structure, and the instruction about the test equipments used could be found in our published work38. Plasma synthesis is a complex heat and mass transfer process. The synthesis reaction is completed in tens of milliseconds in the field of electromagnetic and concentration. Moreover, in such a short reaction time, numerous variables are involved, including phase conversion, thermo fluid interactions and so on. Therefore, proper plasma parameters are very important for stable operation, which are given in Table S1 (Supporting Information). Electrochemical Test The electrochemical properties of NiO nanocubes were tested by assembled into a CR2025 type coin-half-cell in glove box full of argon. The working electrode was prepared by mixing slurry: there were 80% NiO nanocubes of weight ratios as the active materials, the amount of polyvinylidene fluoride (PVDF) mixed with N-methyl pyrrolidinone (NMP) is 10% and acetylene black (AB) is 10%. After stirring for 45 min, the slurry was homogeneous and coated onto a copper foil with a mass loading of 2.4 mg/cm2. The Cu foil coated with slurry was dried at 120℃ for 12 h in vacuum. Then it was cut into disks with a diameter of 12.0 mm using a slicer and dried at 120℃ for another 12 h. The counter electrode is Li disk with the same diameter. Between the 18


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working electrode and Li disk, a polypropylene microporous film (Celgard 2400) was used as the diaphragm. The electrolyte was made by mixing the ethylene carbonate and dimethyl carbonate with volume ratio of 1:1 into lithium hexafluorophosphate solution with a concentration of 1 mol L-1. The electrochemical performances of assembled cells were tested by Wuhan Land testing instrument (CT2001A). The cycling performance was tested with a voltage window from 0.01 to 3V at a current of 0.2 C. And the rate performance was conducted at 0.1 C, 0.2 C, 0.5 C and 1.0 C. Cyclic voltammetry (CV) and electrochemical impedance were obtained by using an Electrochemical workstation (CH Instruments Model 660E). Construction of the NiO nanocubes based LIBs A nano-battery with the working electrode of NiO nanocube was conducted using in situ TEM (JEOL-2100F) equipped with a “Nanofactory Instruments AB” STM-TEM holder. In the nano-battery device, the working electrode-NiO nanocubes were attached to the Au wire and inserted in a removable piezo-manipulator. The Li metal was the counter electrode and attached to the opposite W wire. On the surface of Li metal, there is a naturally grown lithium oxide layer, which was served as a solid electrolyte for the transportion of Li+. When a -2 V potential was added between the NiO nanocubes and lithium metal, the lithiation process took place quickly.

ASSOCIATED CONTENT Supporting information: The supporting information is available free of charge on the ACS publications website at DOI: XXXXX 19



Schematic illustration and digital photo of the RF induction thermal plasma, detailed parameters for RF induction thermal plasma processing, Raman pattern of the asprepared NiO nanocubes, XPS spectra of NiO nanocubes: survey scan, the performance of NiO and NiO-based composite anodes as lithium batteries, the volume change of c-NiO for lithiation along the , and directions, detail information about theoretical calculations.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by Beijing Natural Science Foundation (BNSF No.2184126) and by the National Natural Science Foundation of China (NSFC No. 21805282; NSFC No.11535003) and by the State Key Laboratory of Multi-phase Complex Systems for Materials Crystallization science.

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