MOF-Derived Long Spindle-like Carbon-Coated Ternary Transition-Metal-Oxide Composite for Lithium Storage.

Fe3O4 is a promising alternative for next-generation lithium-ion batteries (LIBs). However, its poor cycle stability due to the large volume effect during cycling and poor conductivity hinders its application. Herein, we have successfully designed and prepared a carbon-coated ternary transition-metal-oxide composite (noted as (FeCoNi)3O4@C), which is derived from FeCoNi-MOF-74 (denoted as FeCoNi-211-24). (FeCoNi)3O4@C perfectly inherited the long spindle-shaped precursor structure, and (FeCoNi)3O4 particles grew in situ on the precursor surface. The ordered particles and the carbon-coated structure inhibited the agglomeration of particles, improving the material's cycle stability and conductivity. Therefore, the electrode exhibited excellent electrochemical performance. Specifically, (FeCoNi)3O4@C-700 presented excellent initial discharge capacity (763.1 mAh g-1 at 0.2 A g-1), high initial coulombic efficiency (73.8%), excellent rate capability, and cycle stability (634.6 mAh g-1 at 0.5 A g-1 after 505 cycles). This study provides a novel idea for developing anode materials for LIBs.

Introduction

Nowadays, rechargeable lithium-ion batteries (LIBs) have become an irreplaceable part of energy storage devices (ESDs) in various fields, such as phones, digital cameras, and personal computers, for their high energy density, high working voltage, fast charge rate, and long cycle life.[1] However, the demand for energy increases rapidly with science and technology development, which requires updating the ESDs. Anode materials are important battery components that determine the performance of batteries. Due to their limited theoretical capacity (372 mAh g–1) and poor performance, current commercial anode graphite gradually can hardly meet the energy demand presently.[2] Transition-metal oxides (TMOs) show higher operating voltages and better safety than graphite-based anode materials. Besides, their various chemical valence states and different morphological characteristics make them promising anode materials for next-generation LIBs.[3]

Among TMOs, Fe3O4 especially exhibits a high theoretical specific capacity and is eco-friendly, naturally abundant, and cost-effective.[4] However, the huge volume effect and kinetic constraints result in a poor cycle and rate performance during operation, hindering its application.[5,6] To solve these problems, several studies have been conducted on the following aspects: (1) Preparation of carbon-coated Fe3O4 nanoparticles. Ru successfully prepared N-doped carbon-coated Fe3O4 composites (Fe3O4@NC) by poly(acrylonitrile) (PAN) phase conversion method. The carbon-coated structure can enhance the electron conductivity and buffer the volume change of Fe3O4 nanoparticles during cycling.[7] (2) Preparation of Fe3O4 nanoparticles with a three-dimensional (3D) porous structure. Wu reported a 3D porous Fe3O4 prepared via template-assisted and subsequent electrochemical deposition methods. The porous Fe3O4 electrodes show better cyclability and enhanced rate capabilities attributed to improved electrical contact, fast electron transport, and good strain accommodation of the porous electrodes.[8] Nevertheless, the modification improves the cycle and rate performance of Fe3O4 finitely because of the serious agglomeration of nanoparticles. Hence, it is needed to design the Fe3O4 nanostructure to avoid agglomeration.

A multimetal method was introduced because polymetallic compounds show better electrochemical activity, conductivity, and stability than the corresponding single-metal counterparts when used as electrodes for LIBs.[9] Besides, the volume expansion rate difference between different TMOs can effectively reduce the structural collapse possibility during the cycle. Metal–organic frameworks (MOFs) show apparent advantages of high specific surface area, high porosity, and low density.[10,11] Using MOFs as templates can obtain ternary TMOs with uniform element distribution and convert the organic ligands of MOFs into continuous and uniform carbon coated on the TMOs surface, which can effectively alleviate the agglomeration of nanoparticles.

Herein, (FeCoNi)3O4@C composites were designed and synthesized by a facile one-step pyrolysis method using FeCoNi-211-24 as a template. (FeCoNi)3O4 single-crystal particles grow in situ on the precursor surface, effectively precluding the agglomeration of metal oxides and improving the rate performance. Additionally, the grains and crystal surfaces of (FeCoNi)3O4 nanoparticles provided a huge specific surface area and several active sites for the material, which is beneficial for improving the material’s capacity. Furthermore, the (FeCoNi)3O4 single-crystal particles connected by carbon formed a polycrystalline long spindle-shaped (FeCoNi)3O4@C composite. The existence of carbon species bonds in the single-crystal particles inhibits the agglomeration of nanoparticles and improves the cycle stability, conductivity, and ion transport of materials. This work provides a novel idea for TMOs as anode materials for LIBs.

Experimental Section

Synthesis of FeCoNi-211-24

The FeCoNi-211-24 crystals were synthesized following a reported method.[12] Co(NO3)2·6H2O (0.8384 g), Ni(NO3)2·6H2O (0.8376 g), FeSO4·7H2O (1.6016 g), and 2,5-dihydroxyterephthalic acid (0.72 g) were dissolved in 10 mL of deionized water, and 60 mL of N,N-dimethylformamide (DMF) and 10 mL of ethanol were successively added to the mixed solution. The mixture was dispersed in a cell grinder for 10 min after mixing and then stirred magnetically for 30 min. Then, the prepared solution was transferred to an autoclave and heated at 120 °C for 24 h. After cooling sufficiently, the products were centrifuged and washed with ethanol and deionized water, and then the products were dried in a vacuum oven at 60 °C for 24 h to obtain FeCoNi-211-24.

Synthesis of (FeCoNi)3O4@C

The obtained FeCoNi-211-24 in the first step was placed in a corundum crucible and pyrolyzed in a tubular furnace at 600–900 °C in a nitrogen atmosphere for 2 h. The obtained samples are (FeCoNi)3O4@C, which were denoted as (FeCoNi)3O4@C-600, (FeCoNi)3O4@C-700, (FeCoNi)3O4@C-800, and (FeCoNi)3O4@C-900 according to different preparation conditions.

Material Characterization

X-ray diffraction (XRD, Bruker, D8 Venture) with Cu Kα radiation (λ = 1.5418 Å) was employed to determine the crystallographic phases and phase purity of the products. Field emission scanning electron microscopy (SEM, Gemini-300) and transmission electron microscopy (TEM, JEM-2100F) were applied to characterize the morphology and distribution of samples. X-ray photoelectron spectroscopy (XPS, Scientific K-Alpha) was used to measure the surface chemical states of the products. Raman spectra of anode materials were recorded by a Renishaw (inVia plus) Raman laser microscope. TG-DSC was performed on a NETZSCH (200F3).

Electrochemical Measurements

The obtained material (FeCoNi)3O4@C was applied as the anode. The electrochemical measurements were carried out at room temperature using LIR2032 coin-type half cells. The working electrode was prepared by mixing (FeCoNi)3O4@C, carboxymethylcellulose (CMC), and acetylene black in deionized water with a weight ratio of 8:1:1. The slurry, thoroughly ground in a mortar for 30 min, was coated onto a piece of Cu foil and left to dry at 60 °C under vacuum for 12 h. LIBs were assembled in an Ar-filled glovebox, where water and oxygen concentrations were below 1 ppm. Lithium metal was used as the counter electrode, using a Celgard 2400 membrane as a separator, and 1.1 M LiPF6 in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and vinylene carbonate (VC) (1:1:1 in weight) was used as the electrolyte. Battery test systems (LAND CT2001A) were employed to record the constant current charge and discharge performance of the anode material in the voltage range of 0.01–3.0 V. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) curves were tested at 25 °C with the electrochemical workstation (CHI604E) in the voltage range of 0.01–3 V.

Results and Discussion

Based on the literature[12−14] and combined with the XRD diffraction pattern of FeCoNi-MOF-74 (Figures a, S1, and S2), FeCoNi-211-24 was successfully prepared by a simple hydrothermal method in this study. However, MOFs are seldomly used as electrode materials due to their poor conductivity and cycle stability. Using MOFs as templates or precursors, carbon-coated metal oxides with high porosity can be obtained by controlled pyrolysis reaction.[15] Therefore, (FeCoNi)3O4@C with a long spindle shape, which is electrochemically active and has high conductivity and cycle stability, was synthesized by pyrolyzing FeCoNi-211-24 in an N2 atmosphere at different temperatures.

Figure 1

(a) XRD patterns of FeCoNi-211-24 and (b) XRD patterns and (c) Raman spectra of (FeCoNi)3O4@C-600, 700, and 800. (d) N2 adsorption/desorption curve of (FeCoNi)3O4@C-700.

Figure b shows the phase transition of FeCoNi-211-24 during pyrolysis in a N2 atmosphere. Obviously, the products obtained at different pyrolysis temperatures display a wide peak at 2θ = 22.9°, indicating amorphous carbon formation.[5] The diffraction peaks at 30.1, 35.4, 56.6, and 62.5° correspond to the (220), (311), (333), and (440) planes of (FeCoNi)3O4 phase. The proportion of alloy phases in the product increases continuously as the temperature increases. At 800 °C, the alloy phase replaced (FeCoNi)3O4 became the main product component, and the metal oxide phase completely transformed into the alloy phase at 900 °C (Figure S3).

Electronic conductivity and ion transport properties significantly influence the electrochemical properties. The existence of carbon on the anode surface can effectively improve these properties.[7,16] Therefore, Raman spectroscopy was applied to evaluate the (FeCoNi)3O4@C sample characteristics (Figure c). The two distinct characteristic diffraction peaks near 1300 and 1580 cm–1 are the D band and G band, respectively. The D band measures the C lattice defects, and the G band represents the in-plane stretching vibration of the C sp2 hybridization.[17] The intensity ratio between the D and G bands reflects the surface defects and lattice distortion of the as-prepared samples, indicating the disordered carbon nature.[18]Figure c shows that the ID/IG ratios of the samples are 0.80, 0.89, and 0.91, respectively. These values increase continuously as temperature increases, indicating that the surface defects of (FeCoNi)3O4@C increase continuously. Note that when the pyrolysis temperature increases by 100 °C, the ID/IG value of (FeCoNi)3O4@C-700 increases greatly compared to that of (FeCoNi)3O4@C-600. However, the ID/IG value of (FeCoNi)3O4@C-800 increased slightly, indicating that the temperature increment contributes slightly to the increment in surface defects at 700 °C. The high ID/IG value provides many surface defects and ion storage active sites, which enhance the specific capacity of the materials.[19] Therefore, it can be speculated reasonably that (FeCoNi)3O4@C-700 has better electrochemical performance.

N2 adsorption and desorption isotherms measurement was utilized to study the specific surface area and the porous properties of as-synthesized samples. As shown in Figure d, the specific surface area of (FeCoNi)3O4@C-700 (54.509 m2 g−1) is larger than that of (FeCoNi)3O4@C-800 (10.381 m2 g-1) (Figure S4). The larger specific surface area means that more active sites are exposed and the contact area between electrolyte and material increases, which greatly improves the electrochemical performance.

Figure shows the SEM images of the FeCoNi-211-24 precursor and (FeCoNi)3O4@C samples prepared at different temperatures. Figure a shows a long spindle shape corresponding to the precursor. During pyrolysis, cracks gradually appear on the surface of the long spindle precursor (Figure b) as the temperature increases continuously, and irregular octahedral (FeCoNi)3O4 crystals (Figure S5) grow in situ on the surface. The sample obtained at 700 °C perfectly inherits the unique spindle precursor structure (Figure c) and exposes more (FeCoNi)3O4 grains and crystal planes on the surface; (FeCoNi)3O4 single-crystal nanoparticles connected by the surface carbon formed a long spindle polycrystalline composite (FeCoNi)3O4@C. As the temperature increases, the alloying degree of the (FeCoNi)3O4 continually increases, along with the structural collapse of the precursor. The (FeCoNi)3O4@C-800 sample agglomerated to form a huge polycrystalline particle with a particle size of several microns (Figure d).

Figure 2

(a) SEM images of FeCoNi-211-24 and (b–d) (FeCoNi)3O4@C-600, 700, and 800.

The TEM image (Figure a) confirms that (FeCoNi)3O4@C-700 comprises carbon-coated irregular octahedral nanoparticles (red circle), where the amorphous carbon layer thickness is 3–5 nm (Figure S6). Due to the different atomic radii of Fe, Co, and Ni, the molar ratio content affects the sample’s lattice parameters.[12,20] The high-resolution TEM image (Figure b) shows lattice fringes’ pitches of 0.4703 and 0.2513 nm corresponding to the (FeCoNi)3O4@C(111) and (311) planes. Additionally, several clear electron diffraction rings of (FeCoNi)3O4@C-700 shown in the selected area electron diffraction image (Figure c) indicate that the as-prepared sample is a polycrystalline material comprising single-crystal particles. The well-defined diffraction rings correspond to the (311), (422), and (533) crystal planes of (FeCoNi)3O4. The mapping image of the energy-dispersive system (Figure d–i) shows that Fe, Co, Ni, O, and C are evenly distributed in samples.

Figure 3

(a) TEM image, (b) HR-TEM image, (c) selected area electron diffraction (SAED) pattern , and (d–i) the corresponding elemental mapping distribution of (FeCoNi)3O4@C-700.

To further understand the chemical state and composition of the samples, the electronic structure and elemental valence states of (FeCoNi)3O4@C-700 were analyzed using X-ray photoelectron spectroscopy. The spectrum (Figure a) confirms the presence of Fe, Co, Ni, C, and O in the sample. The peak at 284.77 eV of the C 1s high-resolution XPS spectrum (Figure b) corresponds to the C–C bond, confirming the presence of amorphous carbon. The peaks at 285.79 and 288.98 eV are attributed to C–O and O–C=O.[10,21] The peak at 530.10 eV of the O 1s spectrum corresponds to (FeCoNi)–O. The binding energies at 531.92 and 533.82 eV are the bonds between carbon- and oxygen-containing groups on the surface of metal oxides, which are C–O, and −O–C=O (Figure c).[10]Figure d shows the Fe state; the Fe 2p spectrum can be decomposed into five peaks. The peaks at 710.41 and 723.93 eV reveal Fe2+ existence. The peak at 718.31 eV is attributed to the satellite, which relates to the oscillatory excitation of high spin Fe2+, whereas the peaks located at 712.45 and 726.24 eV correspond to Fe3+.[22,23] For the Co 2p spectrum (Figure e), the peaks at 781.41 and 796.76 eV are attributed to the Co 2p3/2 and Co 2p1/2 electrons of Co2+, whereas the satellite peaks are observed at 785.26 and 802.63 eV. Additionally, the peaks detected at 789.0 eV correspond to the status of metallic Co.[24] Three unique Ni statuses can be observed by deconvoluting the Ni 2p spectrum (Figure f), which are Ni, Ni2+, and satellites. The two distinct peaks at 852.56 and 867.38 eV correspond to metallic Ni, where the binding energies at 855.95 and 873.93 eV relate to Ni 2p3/2 and Ni 2p1/2 electrons, respectively.[12,25] Compared with the pure metallic Fe, Ni, and Co species, the binding energy of the three metal elements drifted positively, indicating better conductivity.[13,26]

Figure 4

(a) XPS spectra, (b) C 1s spectrum, (c) O 1s spectrum, (d) Fe 2p spectrum, (e) Co 2p spectrum, and (f) Ni 2p spectrum of (FeCoNi)3O4@C-700.

Furthermore, the electrochemical performance of (FeCoNi)3O4@C was evaluated as an anode material for LIBs (Figure ). Figure a shows the CV curves of (FeCoNi)3O4@C-700 at 0.1 mV s–1. During the initial lithiation, three reduction peaks are observed at 0.96, 0.52, and 0.01 V, respectively. The reduction peak at 0.96 V is attributed to the inserting reaction, which produces Li[(FeCoNi)3O4].[5,21] The reduction peak at 0.52 V relates to two factors. Owing to the conversion reaction, the (FeCoNi)3O4 phase transforms into the (FeCoNi)0 phase; however, the peak is related to the electrolyte decomposition, which forms the solid electrolyte interface (SEI) layer. The peak near 0.01 V relates to Li+ intercalation into the amorphous porous carbon, causing the carbon matrix lithiation.[17,27] During the first anode cycle, two oxidation peaks were detected at 1.6 and 1.8 V, corresponding to the reversible oxidation of (FeCoNi)0 to (FeCoNi)3O4. Subsequently, the CV cycle curves and peak locations of the sample almost overlap, indicating good cycle stability and reversibility. The reduction peak at 1.5 V corresponds to the material’s deinserting reaction, whereas peaks at 0.91 and 0.73 V are attributed to the (FeCoNi)3O4 to (FeCoNi)0 reduction reaction. The cyclic process is similar to those in the literature.[8,10,28] Note that the reduction peak at 0.52 V disappears in the first cycle, indicating the formation of the stable SEI film on the material’s surface, which enhances the rate performance and cycle stability of the material.[17] The reactions involved in the circulation process are as follows

Figure 5

(a) CV curves at a scan rate of 0.1 mV s–1; (b) galvanostatic discharge–charge curves at a current density of 200 mA g–1 of (FeCoNi)3O4@C-700; (c) rate performance of sample (FeCoNi)3O4@C-600, 700, and 800 at different current densities from 0.1 to 2 A g–1; (d) comparison of cycle performance of samples (FeCoNi)3O4@C-600, 700, and 800 at a current density of 200 mA g–1; and (e) cycling performance and coulombic efficiency of sample (FeCoNi)3O4@C-700 at 500 mA g–1.

Figure b exhibits the (FeCoNi)3O4@C-700 galvanostatic charge–discharge (GCD) curves of the 1st, 2nd, 3rd, 50th, 100th, and 200th cycles at a current density of 200 mA g–1. (FeCoNi)3O4@C-700 presents initial discharge and charge-specific capacities of 763.1 and 563.4 mAh g–1, respectively, with an initial coulombic efficiency (ICE) of 73.8%. The ICE values of (FeCoNi)3O4@C-600 and (FeCoNi)3O4@C-800 are 63.3 and 65.2%, respectively (Figure S7). The irreversible capacity in the first cycle was caused by the formation of SEI film and electrolyte decomposition.[17,23,29] A discharge platform can be observed at ∼0.9 V, and an ultralong plateau appears at ∼0.7 V in the first cycle. Discharge voltage plateaus located at ∼1.6 and 1.0 V and a charge voltage platform at ∼1.7 V can be observed in the subsequent cycle, corresponding to the redox in the process. The GCD results are consistent with the CV data. Moreover, from the second cycle, the coulombic efficiency (CE) of (FeCoNi)3O4@C-700 recovered to 97.36%, indicating the sample’s excellent cycle reversibility.

The rate performance of (FeCoNi)3O4@C-600, (FeCoNi)3O4@C-700, and (FeCoNi)3O4@C-800 was measured at current densities of 0.1, 0.2, 0.5, 1, 2, and 0.1 A g–1 (Figure c). The reversible specific capacities of (FeCoNi)3O4@C-700 are 572.5, 512.4, 471.1, and 386.6 mAh g–1, corresponding to 0.1–1 A g–1. Impressively, the reversible specific capacities of (FeCoNi)3O4@C-700 remained at 558.3 mAh g–1 when the current density dropped to 0.1 A g–1, indicating the excellent reversibility of (FeCoNi)3O4@C-700. Surprisingly, (FeCoNi)3O4@C-800 shows reversible capacities of ∼280 mAh g–1 (Figure S8); when it was exposed at a high current density of 2 A g–1 for 800 cycles, the CE value is close to 100%, indicating its excellent cycle stability at high current density.

Furthermore, the lithium storage stability of the electrode was investigated at 200 mA g–1 (Figure d). The initial discharge specific capacity of (FeCoNi)3O4@C-700 is 763.1 mAh g–1 because of the distinct structural and morphological reconstructions, which caused a large volume change, resulting in a decreased capacity in the first 30 cycles. However, the reconstruction provides new active sites and surfaces, indicating that the surface reactions occur even with higher kinetics, leading to continuous capacity increment in the subsequent cycle.[17,21,23] After 330 cycles, the reversible specific capacity and CE of (FeCoNi)3O4@C-700 are ∼653.4 mAh g–1 and 100%, respectively. Under the same conditions, the after-cycling reversible specific capacities of (FeCoNi)3O4@C-600 and (FeCoNi)3O4@C-800 are 527.8 and 120.6 mAh g–1, respectively. According to Figure d, the structure of (FeCoNi)3O4@C-800 was collapsed, which seriously affected its electrochemical performance. However, (FeCoNi)3O4@C-700 maintained the long spindle-shaped structure with more (FeCoNi)3O4 transition-metal-oxide crystal particles formed on its surface. The active sites were increased, resulting in a large increase in electrochemical performance. To prove the excellent electrochemical performance of (FeCoNi)3O4@C-700, the long-cycling performance was investigated at a high current density of 0.5 A g–1. Figure e shows that the specific discharge capacity of (FeCoNi)3O4@C-700 is 634.6 mAh g–1 after 505 cycles (CE is 99.22%). The (FeCoNi)3O4@C-700 sample comprises single-crystal particles with controlled shapes and particle sizes, perfectly inherits the skeleton structure of the precursor FeCoNi-211-24, and forms a unique long spindle-shaped carbon shell-coating structure, showing high capacity and excellent cycle stability. Therefore, the impressive long-cycling stability of the (FeCoNi)3O4@C-700 electrode is attributed to the unique carbon shell structure, which accelerates electron conduction and effectively inhibits the electrode volume expansion in the cycle process.[19,29,30]

Figure S9 shows the electrochemical impedance spectra (EIS) of (FeCoNi)3O4@C-600 and (FeCoNi)3O4@C-700. The high- and medium-frequency semicircles are attributed to the contact and charge transfer impedances, respectively. The inclined straight line is associated with Warburg impedance corresponding to the lithium-diffusion process. The diameters of the high-frequency and intermediate-frequency semicircles produced by (FeCoNi)3O4@C-700 are smaller than that of (FeCoNi)3O4@C-600, indicating that (FeCoNi)3O4@C-700 has better conductivity and ionic conductivity.

Additionally, the (FeCoNi)3O4@C-700 electrode was tested at different sweep rates of 0.1–2.0 mV s–1 in the potential range of 0.01–3.00 V to explore the electrode electrochemical kinetics. The CV curves at different scanning rates (Figure a) show similar shapes. According to previous studies, electrochemical storage behavior can be subdivided into faradic (charge transfer) and nonfaradic (pseudo-capacitive behavior) processes. The peak current (i) and scanning rate (v) are utilized to study pseudo-capacitance by the following formulas[17−19]

Figure 6

Electrochemical kinetic analysis of the (FeCoNi)3O4@C-700 electrode. (a) CV curves at different scan rates from 0.1 to 2 mV s–1; (b) b value calculated by log(peak current) vs log(scan rate); (c) diffusion contribution and capacitance contribution at 0.5 mV s–1; and (d) comparison of diffusion contribution and capacitance contribution at various scan rates.

Generally, the process is diffusion-controlled when the adjustable parameter (b) is close to 0.5, but pseudo-capacitance-controlled when b approaches unity. Figure b shows the relationship between log(i) and log(ν). Through simulation and calculation, the b values corresponding to the five peaks are 0.82, 0.81, 0.84, 0.77, and 0.63, indicating that the lithium storage behavior of (FeCoNi)3O4@C-700 is mainly pseudo-capacitance-controlled.

According to the equation describing the relationship between capacitance and diffusion contributions (i(v) = k1ν + k2ν1/2),[17,31] the capacitance contribution of (FeCoNi)3O4@C-700 is 64.52% at a scanning rate of 0.5 mV s–1 (Figure c). Figure d shows that the capacitance contribution rate increases as the scanning rate increases. When the scanning speeds are 0.1 and 2 mv s–1, the capacitance contribution rates are 55 and 95%, respectively. Thus, the capacitance behavior in the electrode is closely related to electrochemical kinetics. A high-capacitance contribution rate indicates the rapid transfer of Li+, reflecting an excellent rate performance.[17,19,32]

Conclusions

Herein, a long spindle-like (FeCoNi)3O4@C composite was designed and synthesized by a facile one-step high-temperature pyrolysis method using the FeCoNi-211-24 template, which was fabricated by a simple hydrothermal method. The (FeCoNi)3O4@C-700 sample inherits the long spindle structure of FeCoNi-211-24. The (FeCoNi)3O4 particles grown in situ on the precursor surface and connected by amorphous carbon formed a long polycrystalline spindle (FeCoNi)3O4@C composite. The structure exposed grains and crystal planes to preclude the agglomeration of metal oxides and provide an enormous specific surface area and several active sites for the material, effectively improving the electrochemical performance of the material. The carbon layer in the material enhances bonding and can effectively improve the material’s conductivity and ion transport. The anode shows excellent initial discharge capacity (763.1 mAh g–1 at 0.2 A g–1), a high ICE of 73.8%, rate capability, and cycle stability (634.6 mAh g–1 at 0.5 A g–1 after 505 cycles). By designing and preparing (FeCoNi)3O4@C as the anode material of LIBs, excellent electrode electrochemical properties are observed.