Amorphous Red Phosphorus Embedded in Highly Ordered

Feb 11, 2016 - Here, we significantly improves both lithium storage and sodium storage performance of red P by confining nanosized amorphous red P int...
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Letter pubs.acs.org/NanoLett

Amorphous Red Phosphorus Embedded in Highly Ordered Mesoporous Carbon with Superior Lithium and Sodium Storage Capacity Weihan Li,† Zhenzhong Yang,∥ Minsi Li,† Yu Jiang,† Xiang Wei,† Xiongwu Zhong,† Lin Gu,∥,⊥ and Yan Yu*,†,‡,§ †

Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China

‡

Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, China State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, China

§

∥

Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China ⊥ Collaborative Innovation Center of Quantum Metter, Beijing 100190, China S Supporting Information *

ABSTRACT: Red phosphorus (P) have been considered as one of the most promising anode material for both lithium-ion batteries (LIBs) and (NIBs), because of its high theoretical capacity. However, natural insulating property and the large volume expansion of red P during cycling lead to poor cyclability and low rate performance, which prevents its practical application. Here, we significantly improves both lithium storage and sodium storage performance of red P by confining nanosized amorphous red P into the mesoporous carbon matrix (P@CMK-3) using a vaporization−condensation−conversion process. The P@CMK-3 shows a high reversible specific capacity of ∼2250 mA h g−1 based on the mass of red P at 0.25 C (∼971 mA h g−1 based on the composite), excellent rate performance of 1598 and 624 mA h g−1 based on the mass of red P at 6.1 and 12 C, respectively (562 and 228 mA h g−1 based on the mass of the composite at 6.1 and 12 C, respectively) and significantly enhanced cycle life of 1150 mA h g−1 based on the mass of red P at 5 C (500 mA h g−1 based on the mass of the composite) after 1000 cycles for LIBs. For Na ions, it also displays a reversible capacity of 1020 mA h g−1 based on the mass of red P (370 mA h g−1 based on the mass of the composite) after 210 cycles at 5C. The significantly improved electrochemical performance could be attributed to the unique structure that combines a variety of advantages: easy access of electrolyte to the open channel structure, short transport path of ions through carbon toward the red P, and high ionic and electronic conductivity. KEYWORDS: Lithium-ion batteries, sodium-ion batteries, anodes, red phosphorus, CMK-3

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(NIBs) are going on fast development as alternatives to LIBs.4−6 The demand for higher energy density LIBs facilitates the study

he rapid development of portable electronics and hybrid electric vehicle (HEV) markets promotes the research of electric energy storage systems. Among them, lithium-ion batteries (LIBs) have attracted intense attention, due to their high energy density and long cycle lifetime.1−3 In addition, benefiting from abundant resources reserve and low cost, sodium-ion batteries © XXXX American Chemical Society

Received: September 25, 2015 Revised: February 3, 2016

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Nano Letters of various LIBs electrode materials.7−11 The same impetus also occurs in current NIBs research.12−14 Recently, phosphorus (P) has been demonstrated as one of the most promising candidate anode materials because of its high theoretical capacity for both LIBs and NIBs (2595 mA h g−1, based on reactions, 3 Li/Na + P → Li3P/Na3P).15,16 Among three main allotropes of solid phosphorus (white, red, black), white P is chemically unstable and flammable, due to weak bond energy in the tetrahedral P4 structure, which is not proper for application in LIBs/NIBs.17 Recently, black P and red P have received much interest due to their high lithium and sodium storage capacity.17−19 Sun et al. have presented improved lithium storage performance of black phosphorus by forming a stable phosphorus−carbon bond and investigated the sodiation mechanism of black P and showed remarkable sodium storage performance of a phosphene− graphene composite.17,20 Red P is another promising anode material because it is commercial available and environmentally benign. However, red P face the following major challenges, which limit its practical applications: (i) red P has low electronic conductivity (∼10−14 S cm−1);17 (ii) red P undergoes huge volume change during Li+/Na+ insertion/extraction (∼300% and ∼400% for Li+ and Na+ insertion/extraction, respectively).17,20−22 All of these would result in fracture of electrode material during cycling, fast capacity fade, and poor electrochemical performance at high current densities. To address these issues, some groups have been trying to design and construct novel microstructured/nanostructured P-based materials to improve the electrochemical performance, including the introduction of conductive additives to improve electron conductivity and accommodate volume change during cycling, preparation of nanostructured/amorphous phosphorus to minimize stress from volume change and shorten Li+/Na+ diffusion paths, and formation of the carbon−phosphorus bond to stabilize phosphorus during cycling.16,17,22−26 Li et al. have reported that P/CNT composite could improve the electron conductivity of P and enhance the cycle stability.27 Our previous work16 and Wang et al.’s work28 show that the rate performance of red P could reach ∼400 mA h g−1 at ∼10 C for LIBs. Qian et al. have presented reversible 3-Li storage reactions of amorphous P and improved cyclability and rate performance through simple high energy ball-milling process.26 Among various approaches to minimize the mechanical stresses induced by volume change, the construction of an amorphous P composite has been proven to be one of the most effective ways in accommodating the volume changes of electrode materials during cycling.29,30 Although the cyclability of these P-based materials are promising for LIBs, the reversible capacity of red P for NIBs is unsatisfactory and, more importantly, could be only obtained at low current density (less than 2 C), which indicates very sluggish kinetics for the Na storage process. Recently, Zhu et al. have presented improved cycle stability of red P in NIBs by preparing one red P-single-walled carbon nanotube composite (∼300 mA h gcomposite−1 after 2000 cycles at 2Agcomposite−1) and good rate performance, which needs further improving (the highest current density in this work is only ∼2 C).21 For lithium insertion, many researchers have demonstrated that the fast kinetics can be achieved by introducing nanoporosity to the electrode and downsizing the active material size.31,32 Inspired by these pioneer works and in order to further improve the rate capability of red P for Na storage, we should combine the abovementioned strategies. Herein, we confined amorphous red P in highly ordered channels of mesoporous carbon matrix, CMK-3 (donated as

P@CMK-3) by vaporization−condensation−conversion strategy. CMK-3 has been widely utilized in electrode materials in both LIBs and NIBs,33−37 due to uniform diameter pores, high pore volume, and excellent conductivity. The red P was encapsulated in CMK-3 combines a variety of advantages: First, the CMK-3 matrix not only provides a rational solution to improve the electronic conductivities of red P but also accommodates the volume change of P during cycling. Second, nanosized red P was confined in the channel, which could reduce the diffusion length of Li+/Na+ and e−. Third, the interconnected and continuous pores of CMK-3 provide easy access of electrolyte to nanosized P particles. Benefiting from this unique hybrid nanostructure, P@CMK-3 delivers superior lithium and sodium storage capacity. It shows a high reversible specific capacity of ∼2250 mA h g−1 based on the mass of red P (∼971 mA h g−1 based on the composite) at 0.25 C and significantly enhanced cycle life of 1150 mA h g−1 based on the mass of red P (500 mA h g−1 based on the mass of the composite) at 5 C after 1000 cycles for LIBs. The behavior in terms of Na-ion storage performance of 1020 mA h g−1 based on the mass of red P (370 mA h g−1 based on the mass of the composite) maintained after 210 cycles at 5C is unprecedented. Figure 1A shows a schematic illustration of the process for preparing the P@CMK-3 by a vaporization-condensation-

Figure 1. (A) Schematic illustration of the preparation process for the P@CMK-3 material. (B) Schematic illustration of the lithiation/ sodiation process of red P particles, red P particles-carbon core−shell composite, and nanostructured red P confined in the channels of CMK-3 in LIBs and NIBs.

conversion process.16 During the process, CMK-3 and commercial red P were separately placed in a sealed vessel, full of argon as protection gas. After heated to above sublimation temperature of red P, P vapor would diffuse into the mesopores of CMK-3 by pressure differences and condense to be white P in the channels. By subsequent conversion of white P to red P at 260 °C, nanostructured amorphous red P would be confined in the channels of CMK-3. After washing with CS2 to remove the unconverted white P and obtain void space in the channels, we finally obtained chemically stable P@CMK-3 material. As shown in Figure 1B, red P particle or carbon coated red P particle cannot allow long cycle life, due to the huge volume change of red P during cycling.17 Our design of nanosized red P embedded in the channels of CMK-3 can accommodate the expansion of red P after lithiation/sodiation without cracking CMK-3. In addition, the CMK-3 matrix provides large contact area for electrolyte access and good transport kinetics for both electrons/ions. B

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Figure 2. SEM micrographs of CMK-3 (A) and P@CMK-3 (B); TEM micrographs of CMK-3 (C) and P@CMK-3 (D).

Figure 3. High angle annular dark-field STEM (HAADF-STEM) image (A) and corresponding carbon (B) and phosphorus (C) elemental mapping of P@CMK-3; (D) line profile across A, B, and C that show the relative intensities of the HAADF-STEM image and the two elements.

The scanning electron microscopy (SEM) images in Figure 2A reveals the morphology of CMK-3, presenting rod-like macrostructure with uniform size of 2−3 μm. The 1D highly ordered porous structure of CMK-3 with uniform pore diameter of ∼4 nm is confirmed by the transition electron microscopy (TEM) images in Figure 2C. After impregnation of red P, the morphology of P@CMK-3 (Figure 2B) remains unchanged without fracture and no obvious red P residue on the surface of CMK-3, indicating that most of red P has been encapsulated in CMK-3. The result agrees with the partially blocked channels of P@CMK-3 in the TEM image (Figure 2D), ascribed to the infiltration of red P in the highly ordered channels. The infiltration also leads to the decrease of Brunauer−Emmett−Teller (BET) specific surface area (1128.3 m2 g−1 of CMK-3 to and 14.02 m2 g−1 of P@CMK-3) and pore volume (see Supporting Information, Figure S1).35 As shown in Figure S1A, the nitrogen adsorption−desorption isotherms of CMK-3 is one typical IV isotherm, presenting one typical feature of mesoporous structures with a clear H1 hysteresis loop and a narrow mesopore distribution peaked at ∼4 nm, corresponding to the TEM images of CMK-3 (Figure 2C). After confining red P in the mesopores, the hysteresis loop disappears, and the mesopore size distribution region decreases dramatically, indicating the occupying of red P in mesopores (see Supporting Information, Figure S1). To further confirm the dispersion of red P in P@CMK-3, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was carried out (Figure 3). The contrast of HAADF-STEM images exhibits an approximate Z1.7 dependence (where Z is the atomic number). In Figure 3A, the brighter areas correspond to red P with the higher atomic number, the darker areas corresponding to carbon, indicating that red P is distributed in the channels of CMK-3. Moreover, the elemental mapping of C and P corresponding to Figure 3A agrees well with the expected P@CMK-3 structure, as shown in Figure 3B,C, respectively, revealing the red P conformal dispersion along the channel of CMK-3 with void space. This structure is further confirmed by the line profile across the Figure 3A−C, as

shown in Figure 3D, which displays the relative intensity of the HAADF-STEM image and these two maps. In addition, an EDX mapping result at lower magnification (see Supporting Information, Figure S2) suggests the uniform distribution of red P in the CMK-3. The content of red P in P@CMK-3 was determined to be 31.54 wt % through thermogravimetric analysis (TGA) (see Supporting Information, Figure S3). Figure 4A represents the XRD patterns of P@CMK-3, CMK-3, and commercial red P. For CMK-3, two broad peaks at 2θ ≈ 25 and 45° correspond to graphitic structure, indicating a low degree of graphitization, in accordance with the result of Raman spectrum of CMK-3 (Figure 4B). After infiltrating red P into CMK-3, P@CMK-3 shows the XRD pattern of simple combination of CMK-3 and amorphous red P. In addition, both XRD peaks and Raman peaks (Figure 4B) of red P in P@CMK-3 are weaker than that of pure red P, which could attributed to the confinement of nanosized red P in CMK-3.38 The intensity ration of the D band to G band of P@CMK-3 is almost the same as that of CMK-3, and no more peaks are found for P@CMK-3 except these of CMK-3 and red P, indicating no interaction or bonding formed between red P and CMK-3.17 The electrochemical performance of P@CMK-3 was tested for LIBs and NIBs, respectively. Figure 5A,B displays cyclic voltammograms (CV) curves of P@CMK-3 composite in LIBs and NIBs, respectively. For LIBs, only one clear cathodic peak at ∼0.2 V appears in the first discharge process, ascribed to the activation process of red P during lithium insertion.22,28 Afterward, P@CMK-3 shows three cathodic peaks at ∼0.65, 0.33, and 0.01 V. The first two peaks are ascribed to the lithiation process to form LixP (x = 1−3), the last peak at 0.01 V results from the lithium insertion into CMK-3.22,39 For the anodic scan, three peaks at 1.1, 1.3, and 1.65 V could reveal the stepwise delithiation process from lithium insertion state to extraction state of P, combined with one weak peak at ∼0.2 V corresponding to the lithium extraction from CMK-3. The high reversibility of CV curves after the first cycle C

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Figure 4. (A) XRD patterns and (B) Raman spectra of P@CMK-3, CMK-3, and commercial Red P. In Raman spectra, bands centered at ∼1348 and ∼1589 cm−1 were presented as D-band and G-band, revealing defects and disorder portions and the graphitic layers, respectively. The RI (RI = ID/IG) value corresponds the disorder degree of carbon (0.948 and 0.938 for CMK-3 and P@CMK-3, respectively).

Figure 5. Cyclic voltammograms of P@CMK-3 at a scan rate of 0.2 mV s−1 for LIBs (A) and NIBs (B). Voltage profiles of P@CMK-3 electrode for (C) LIBs cycled between 0.001 and 2.5 V vs Li+/Li at a cycling rate of 0.25 C and (D) NIBs cycled between 0.001 and 2.0 V vs Na+/Na at a cycling rate of 0.2 C. The capacity here was calculated based on the mass of red P.

indicates good cycling stability of P@CMK-3 in LIBs. Figure 5B shows the CV curves of P@CMK-3 for NIBs. For the anodic scan, a stepwise sodium extraction from Na3P also generates three peaks at 0.52, 0.7, and 1.42 V, the same as that in LIBs. In the first cathodic scan, only one broad and large peak between 0.45 and 0 V is observed, except an irreversible peak at ∼0.7 V in the first discharge process belonging to the decomposition of electrolyte to form solid electrolyte interface (SEI). Afterward, a cathodic peak at ∼0.35 V is developed at the third cycle with further sodiation of red P at ∼0.001 V, an indication of enhanced sodiation kinetics, in accordance with enhanced desodiation kinetics ascribed to the increased peak current in the subsequent anodic scans.21

Figure 5C represents the voltage profiles of P@CMK-3 for LIBs cycled at a current density of 0.25 C between 0.001 and 2.5 V vs (Li+/Li), corresponding to the typical characteristic of red P.16,23 The P@CMK-3 delivers initial charge capacity of 1128.6 mA h g−1 based on the mass of the composite, while the CMK-3 shows initial charge capacity of 499.2 mA h g−1 at 0.25 C. So the specific capacity contribution of red P in P@CMK-3 is 2495 ((1128.6 − 499.2 × 0.6846)/0.3154) mA h g−1 based on the mass of red P, presenting an initial Coulombic efficiency (ICE) of ∼68.2%. The irreversible capacity of the first cycle mainly results from the formation of SEI and irreversible lithium insertion into CMK-3 (Figure S4A).40 For the voltage profiles in D

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Figure 6. Electrochemical performance of P@CMK-3 composite for LIBs and NIBs cycled between 0.001 and 2.5 V vs Li+/Li and 0.001 and 2.0 V vs Na+/Na. Capacity-cycle number curves of P@CMK-3 electrode at a cycling rate of 0.25 C for LIBs (A) and 0.2 C for NIBs (B); (C, D) Capacity of P@CMK-3 composite as a function of discharge rate (0.6−12 C for LIBs and 0.6−9.8 C for NIBs). The capacities here are calculated based on the mass of red P and the composite, respectively.

mass of the composite, it can deliver 795 mA h g−1 after 60 cycles. To further demonstrate the excellent electrochemical performance of P@CMK-3, the capacity contribution from CMK-3 is also measured under identical test conditions as shown in Figure S4C,D (see Supporting Information). The CMK-3 delivers only reversible capacities of 380 mA h g−1 and 150 mA h g−1 for Li+ storage and Na+ storage, respectively. Increasing mass loading of electrodes to 2.2 mg/cm2, the P@CMK-3 composite still showed good cycle stability with a high capacity retention of 92.45% after 45 cycles at 0.25 C in LIBs and 83% after 40 cycles at 0.2 C in NIBs (see Supporting Information, Figure S5), an indication of promising application prospect.20,22 In addition, the weight content of phosphorus in the P@CMK-3 composite was increased to ∼60 wt % to confirm the stability of the structure, which also displays improved lithium storage performance of 1440 mA h g−1 (based on the mass of the composite) at a current density of 200 mA h g−1 (see Supporting Information, Figure S6). In addition, by comparing the current work with higher P content with previous works, P@CMK-3 still shows the better cycle performance (see Supporting Information, Table S1). The rate capability of the anode material is an important performance when used for practical application. Figure 6C,D shows the rate performance of P@CMK-3 for both LIBs and NIBs, respectively. In case of lithium storage, with the gradually increased current densities, P@CMK-3 displays capacities based on the mass of red P of 2320, 2185, 1985, 1930, 1783, 1598, 1200, and 934 at the current densities of 0.6, 1.2, 2.4, 3.6, 4.8, 6.1, 8.5, and 9.8C, respectively. Even at a high current rate of 12C, a stable capacity of 624 mA g h−1 is still maintained, indicating the embedding the red P in CMK-3 is a promising strategy. As for

NIBs (Figure 5D), P@CMK-3 is tested at 0.2 C with a voltage window between 0.001 and 2.0 V (vs Na+/Na). Compare with lithium storage, it shows a lower voltage platform and capacity, which is attributed to the difference between the thermodynamics and kinetics of lithiation and sodiation process.4,41 The SEI formation and irreversible sodiation in CMK-3 also lead to a low ICE of 59.4% for NIBs (Figure S4B). In the first cycle, the P@CMK-3 composite and CMK-3 can deliver initial charge capacity of 965.6 and 235.98 mA h g−1 at 0.2 C, presenting a high specific capacity (2549 mA h g−1 based on the mass of red P). After the initial capacity loss, the CE for both of P@CMK-3 for LIBs and NIBs increase to almost 100%, indicating excellent reversibility for lithium and sodium storage. Figure 6A,B investigates the cycle performance of the P@CMK-3 at current densities of 0.25C and 0.2 C for LIBs and NIBs, respectively. The P@CMK-3 shows excellent cycling stability in both LIBs and NIBs, where the capacity is based on the mass of red P. For LIBs, the P@CMK-3 delivers an initial reversible capacity of 2495 mA h g−1, gradually increasing to 2574 mA h g−1 after 4 cycles (Figure 6A), very close to the theoretical capacity of P (2595 mA h g−1). After 85 cycles, the specific capacity of P@CMK-3 based on red P can remain ∼2240 mA h g−1 (the capacity based on the composite mass reaches 971 mA h g−1 after 85 cycles) with a low capacity deterioration rate of less than 0.1% per cycle compared with the initial charge capacity. In case of Na storage, as shown in Figure 6B, the P@CMK-3 displays good cycle stability from the second cycle onward, delivering discharge capacities based on red P of 2591, 2451, 2336, and 2188 mA h g−1 in the second, 20th, 40th, and 60th cycle at 0.2 C, respectively. Base on the total E

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Figure 7. Excellent cycle performance of P@CMK-3 electrodes for LIBs at 1.2 and 5 C (A) and NIBs at 1 and 5C (B) with activation first at low current density. The capacities here are calculated based on the mass of red P; comparison of utilization of phosphorus in several phosphorus-based composites at higher current densities reported recently for LIBs (C) and NIBs (D). (The comparison of utilization of phosphorus in composites is based on the specific capacity contribution of phosphorus in composites.28 For some works that did not provide the specific capacity contribution of phosphorus, we assume that the capacity contribution of carbon matrix in the composites at higher current densities is negligible and present as high specific capacity of phosphorus as possible. The utilization of phosphorus is calculated by the following equation as: Utilization of phosphorus = [specific capacity contribution of phosphorus/theoretical capacity of phosphorus (2595 mA h g−1)] × 100%.

storage performance of the P@CMK-3 is unprecedented.21 The electrochemical activity of phosphorus (related to the utilization of phosphorus)28 in P@CMK-3 for both LIBs and NIBs at higher current densities is superior to several phosphorusbased composite reported recently (Figure 7C,D), including red phosphorus/carbon nanofibers composite,16 phosphorus/ graphene composites,17,22,24,25 amorphous phosphorus/carbon composites,29,38 nanostructured phosphorus/porous carbon composites,42 and red phosphorus−carbon nanotube composites.21 The exceptional electrochemical performance of the composite is mainly attributed to the novel structure, nanostructured phosphorus confined in highly ordered mesoporous carbon. In accordance with the schematic illustration in Figure 1, the highly ordered mesopores in CMK-3 remain stable after lithiation and sodiation and successfully protect red P from fracture and separation from conductive substrates (see Supporting Information, Figures S8 and S9),43,44 and limit the size of red P to ∼4 nm, leading to short transport length of ions/ electrons along the radial direction of the channels of CMK-3 and the nanosized red P (see Supporting Information, Figure S10).45,46 In addition, conductive mesoporous CMK-3 matrix enhances ionic and electronic conductivity,47 which can be proved by the electrochemical impedance spectroscopy (EIS) results (see Supporting Information, Figure S11A,B). The high frequency semicircles of the composite in LIBs and NIBs after several cycles remain low value, indicating fast Li/Na ions reaction between

NIBs, the specific capacity based on the mass of red P of P@CMK-3 is 2331, 2162, 1984, 1860, 1718, 1500, 1042, 808, and 650 mA g h−1 when the current densities increase from 0.6, 1.2, 2.4, 3.6, 4.8, 6.1, 7.3, 8.5 to 9.8 C. The capacities referring to the P@CMK-3 composite, CMK-3, and red P are presented in the Tables S2 and S3 (see Supporting Information). As shown in Figure 6C,D, when calculating the capacities based on the composite for both LIBs and NIBs, it also delivers excellent rate performance with high capacity retention at higher current densities. Furthermore, the long cycling behavior of P@CMK-3 composite at high current density was examined. Figure 7A shows the lithium storage performance of P@CMK-3 at 1.2 C and 5 C. It displays a reversible charge capacity of 1798 mA h g−1, with the capacity retention of ∼80% after 1000 cycles at 1.2 C. Even cycled at 5 C, a reversible capacity of 1150 mA h g−1 is obtained after 1000 cycles. When used as anode for NIBs (Figure 7B), it can also deliver a high specific capacity of 1600 mA h g−1 after 140 cycles at 1 C and 1020 mA h g−1 after 210 cycles at 5 C, respectively. All of the capacities here are based on the mass of red P. Figure S7A,B shows the capacity retention calculated based on the total mass of the composite and excellent electrochemical performance at 1.2 and 5 C for LIBs (583 mA h g−1 after 800 cycles at 1.2 C and 500 mA h g−1 after 1000 cycles at 5 C), and 1 and 5 C for NIBs (580 mA h g−1 after 140 cycles at 1 C and 370 mA h g−1 after 210 cycles at 5 C). To the best of our knowledge, excellent lithium storage and sodium F

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Central Universities (WK3430000004), the Collaborative Innovation Center of Suzhou Nano Science and Technology.

nanostructured red P and high electron transport rate during the cycle life.9,21 By fitting the impedance spectra to an equivalent electrical circuit, including ohmic resistance of batteries (Ri), surface film resistance and charge transfer at the interface between the electrode and electrolyte (Rsf+ct) in parallel with a constant phase element (CPEsf+ct), and Warburg impedance (Wo).24 For LIBs, the combined resistance Rsf+ct is almost the same (57 Ω) after 10 and 20 cycles, only increasing to 68 Ω after 30 cycles; the Rsf+ct for NIBs after 10, 20, and 30 cycles is 112, 117, and 126 Ω, respectively. The low resistance increase and the almost overlapped Nyquist plots indicate that the formed solid electrolyte interface (SEI) during the initial cycles is stable after subsequent cycles.20,24 The structure stability of the composite is beneficial to the formation of stable solid electrolyte interface (SEI) layer during cycling (see Supporting Information, Figure S11C,D), maintaining nearly 100% Coulombic efficiency and excellent cyclability. In summary, we have developed a facile strategy to prepare nanosized amorphous red phosphorus confined in CMK-3 (P@ CMK-3) through a vaporization−condensation−conversion process. The porous carbon matrix (CMK-3) offers intrinsic open channel structure and ensures high ionic/electronic conductivity. The intimate contact between the CMK-3 and nanosized red P suppresses the growth and agglomeration of red P, leading to reduced diffusion length and fast lithium/sodium storage. Owing to this unique structure, the P@CMK-3 demonstrated a high reversible specific capacity of ∼2250 mA h g−1 based on the mass of red P at 0.25 C (∼971 mA h g−1 based on the composite), excellent rate performance of 1598 and 624 mA h g−1 based on the mass of red P at 6.1 and 12 C, respectively (562 and 228 mA h g−1 based on the mass of the composite at 6.1 and 12 C, respectively), and significantly enhanced cycle life of 1150 mA h g−1 based on the mass of red P at 5 C (500 mA h g−1 based on the mass of the composite) after 1000 cycles for LIBs. As anode for NIBs, a specific capacity of 1020 mA h g−1 based on the mass of red P (370 mA h g−1 based on the mass of the composite) is obtained after 210 cycles at 5 C. The present study clearly demonstrates the feasibility to use red P as a high-performance anode for high-power LIBs and NIBs.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.5b03903. Additional information and figures: Preparation and characterization methods, electrochemical characterization parameters, N2 sorption/desorption result, EDX elemental mapping images, TGA results, electrochemical performance, comparison of electrochemical performance, SEM, TEM and HRTEM images, Nyquist plots (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*\Tel.: +86-551-63607179. E-mail address: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 21373195, No. 51522212 and No. 51421002), the “Recruitment Program of Global Experts”, the program for New Century Excellent Talents in University (NCET-12-0515), the Fundamental Research Funds for the G

DOI: 10.1021/acs.nanolett.5b03903 Nano Lett. XXXX, XXX, XXX−XXX

Letter

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DOI: 10.1021/acs.nanolett.5b03903 Nano Lett. XXXX, XXX, XXX−XXX