材料化學(xué)翻譯

1、Journal of Materials Chemistry A材料化學(xué)雜志第 10 頁(yè) 共 10 頁(yè)P(yáng)APERView Article OnlineView Journal | View IssueSynthesis and lithium-storage properties of MnO/ reduced graphene oxide composites derived from graphene oxide plus the transformation of Mn(VI) to Mn(II) by the reducing power of graphene oxide一氧化錳的合

2、成和鋰存儲(chǔ)特性減少了氧化石墨烯的復(fù)合材料，而后者源于氧化石墨烯以及Mn（VI)轉(zhuǎn)化Mn(II)過(guò)程中，通過(guò)降低氧化石墨烯能量生出的轉(zhuǎn)化物In this report, a novel method is proposed to prepare MnO/reduced graphene oxide (rGO) composites via calcining the precursors (i.e. d-MnO2/graphene oxide composites) at 500 C in Ar using no external reducing gas, in which graphene

3、oxide (GO) successfully serves as a reductant by releasing CO during its thermolysis for the first time.By controlling the initial ratios of GO to KMnO4, dierently composed precursors can be obtained via the redox reaction between GO and KMnO4, then leading to the formation of composites with dieren

4、t MnO/rGO ratios and dispersion of MnO on the rGO surface (denoted as MGC1 and MGC2). When applied as an active material in lithium ion batteries, MGC1 shows excellent cycling performance and capacity retention. Under 100 and 200 mA g -1, MGC1 could deliver reversible capacities as high as 900 and 7

5、50 mA h g 1, respectively, after more than 100 cycles. Considering the simple operation and low energy consumption in the whole material synthesis processes, the present strategy is feasible and eective for practical application. Even more importantly, the reductibility of graphene oxide upon thermo

6、lysis is utilized for the first time, which is meaningful for its extension in synthesis of functional nanomaterials.在這份報(bào)告中，提出了制備一氧化錳/還原氧化石墨烯復(fù)合材料的一種新方法，.通過(guò)在氬氣中，500 的條件下 使用沒(méi)有外部的還原性氣體，煅燒前驅(qū)體（i.e .d-二氧化錳/氧化石墨烯復(fù)合材料）,在此過(guò)程中，氧化石墨烯完全可以勝任還原劑的功能，首次熱解，釋放一氧化碳.控制氧化石墨烯（GO）和KMnO4的初始比KMnO4，通過(guò)氧化石墨烯（GO）和KMnO4氧化還原反應(yīng)獲得不

7、同組成的前體，形成的復(fù)合材料具有不同MnO / rGO比率和MnO，rGO表面不同的色散(用MGC1和MGC2表示)。當(dāng)應(yīng)用于鋰離子電池的活性材料時(shí)，MGC1具有優(yōu)異的循環(huán)性能和容量保持率。在100和200 mA g-1下，MGC1可以提供可逆容量高達(dá)900和750 mA h g-1 ，分別在100次以上?？紤]到在整個(gè)材料合成工藝操作簡(jiǎn)單、能耗低，目前的策略是可行的和有效的實(shí)際應(yīng)用。更重要的是，氧化石墨烯對(duì)熱解還原是首次利用，這是其在功能納米材料的合成延伸意義。With the increasing power and energy demand in portable electronic

8、vehicles and devices, great eort has been made in developing new high-performance electrode materials for high-power rechargeable lithium-ion batteries (LIBs).15 Transition metal oxides, such as SnO2,68 TiO2,9 MoOx,10,11 and MnO2,12,13 have been widely studied as anode materials in LIBs since rst pr

9、oposed in 2000 by Poizot et al.14 Among these transition metal oxides, manganese oxides (MnOx) were a promising candidate series because of their relatively low thermodynamic equilib-rium voltage versus Li/Li+,1517 and low electromotive force,1820 as well as their environmental benignity and low cos

10、t. However, there are still several drawbacks such as: (1) the large volume change and gradual agglomeration of metal grains21,22 during the discharge/charge reaction and (2) intrinsically low elec-tronic conductivity, both of which result in the rapid fading of capacities during the cycling process

11、.23 To overcome these challenges, many research studies were focused on the incor-poration of carbon nanomaterials such as carbon nano-tubes2426 and carbon nano bers27 into MnOx to suppress the pulverization and capacity fading.隨著便攜式電子車輛和設(shè)備對(duì)功率和能源的需求，努力開(kāi)發(fā)新的高性能的電極材料為高功率可充電的鋰離子電池（LIBS）。一些過(guò)渡金屬氧化物，如SnO2

12、，MoOx，和MnO2，在作為鋰離子電池的陽(yáng)極材料被廣泛研究，錳氧化物（MnOx）是一種很有前途的候選系列, 因?yàn)槠湎鄬?duì)于 Li/Li+相對(duì)較低的熱力學(xué)平衡電壓，和低電勢(shì)，以及其環(huán)境友好、成本低。然而，仍有一些缺點(diǎn)如：（1）大的體積變化和充放電反應(yīng)過(guò)程中金屬顆粒逐漸集聚，（2）本質(zhì)上低的電子電導(dǎo)率，這兩者導(dǎo)致在循環(huán)過(guò)程中迅速衰敗的能力，為克服這些挑戰(zhàn)，許多研究都集中在碳納米材料如把碳納米管和碳納米纖維加到MnOx中抑制粉化和容量衰減.After the discovery of gra-phene, much interest was paid to graphene/MnOx nano-co

13、mposites for LIBs with high capacity and long-life.23,2830 However, many of these composites were synthesized under severe conditions and usually needed higher cost for calcina-tion. For example, in Sun et al.'s report, by mixing Mn(CH3-COO)2 and GO solutions, and adding hydrazine hydrate, a Mn-

14、precursor/graphene intermediate was obtained, which was then annealed at 500 C in a 5% H2/Ar atmosphere for 5 h to obtain the nal MnO/graphene composite.31 A similar strategy was used for a N-doped MnO/graphene hybrid by calcining a precursor, i.e. Mn3O4/graphene, at 800 for 5 h under a NH3 atmosphe

15、re.32 In Qian's group, the precursors MnOOH nano-wires were rst synthesized through a hydrothermal procedureand a er the following calcination in air, Mn2O3 nanowires were obtained. The final MnOC coreshell nanowires were produced by exposing these Mn2O3 nanowires to argon and an acetylene/argon

16、 gas mixture at 500 .石墨烯被發(fā)現(xiàn)后，更多的關(guān)注放在石墨烯/氧化錳納米復(fù)合材料具有高容量、長(zhǎng)壽命的鋰離子電池上。然而，這些復(fù)合材料的合成需要在苛刻條件下，通常需要更高的成本。例如，在太陽(yáng)等人的報(bào)告，通過(guò)混合Mn(CH3-COO)2和氧化石墨烯來(lái)解決，加入水合肼，Mn前驅(qū)體/石墨烯得到中間物，然后在5005% H2Ar氣流中煅燒5小時(shí)得到復(fù)合材料，類似的方法被用于摻雜一氧化錳/石墨烯混合煅燒前驅(qū)體獲得最終的一氧化錳/石墨烯復(fù)合材料，即Mn3O4 /石墨烯，在8005 h下氨氣流中.在前組，前體MnOOH納米線首先通過(guò)水熱法合成了33和一個(gè)二以下在空氣中煅燒，得到納米三氧化二錳

17、。最后的MnO C核殼納米線的暴露這些Mn2O3納米線在500時(shí)在氬氣和乙炔/氬氣混合氣體中產(chǎn)生.Dierent from many of the reported studies, we herein introduce MnO/rGO composites via a quite dierent synthesis approach. As reported in many publications,34,35 theoretical and experimental proof has proved that thermal reduction of graphene oxide wou

18、ld release CO and CO2, and the COCO2 ratios were dependent on the thermal conditions. Therefore, in this work, we tried to utilize the reductive CO released from GO to in situ reduce MnO2 in the MnO2/GO composites to obtain MnO/rGO composites without using any external reductive gases, such as H2 an

19、d CO, which makes the synthesis process with less cost and more safety. What is more important, GO is utilized as a solid reductant for the frist time and this valuable nding will arouse much interest in the GO research for material synthesis.不同于許多研究報(bào)道,我們這里介紹MnO / rGO復(fù)合材料通過(guò)一個(gè)完全不同的合成方法。在許多出版物報(bào)道,理論和實(shí)驗(yàn)

20、證明熱還原氧化石墨烯會(huì)釋放CO和CO2.CO-CO2的比率依賴于熱條件。因此,在這項(xiàng)工作中,我們?cè)噲D利用氧化石墨烯釋放的還原CO去原地減少M(fèi)nO2/GO 復(fù)合材料中的二氧化錳去獲得MnO / rGO復(fù)合材料不使用任何外部還原氣體,如H2和CO等,使合成工藝成本更低和更安全。更重要的是,去作為一個(gè)固體還原劑.這寶貴的首次發(fā)現(xiàn)會(huì)引起很大的興趣去研究材料的合成In our previous research, it has been proven that the mild redox reaction between graphene oxide and KMnO4 would result in

21、 highly active d-MnO2 nanosheets.36 In the present work, by adjusting the ratio of graphene oxide and KMnO4, dierent contents of graphene oxide can be retained in the d-MnO2/graphene oxide composites. As shown in Fig. 1, we typically tried three dierent weight ratios between KMnO4 and graphene oxide

22、. The redox reaction between the two reactants resulted in three precursors, P-MNP, P-MGC2 and P-MGC1. Through the further calcination under Ar at 500 C, d-MnO2 in the precursors (P-MGC2 and P-MGC1) can be reduced to MnO due to the reductive gas (CO) release from the thermolysis of graphene oxide, r

23、esulting in the formation of MGC2 and MGC1. No graphene oxide was found in the P-MNP, so that afer the calcination under Ar at 500 C, d-MnO2 was transferred to a-MnO2 nanoparticles (denoted as MNP). The general synthesis process for these manganese oxides and their hybrids with graphene is illustrat

24、ed in Fig. 1 (see more experimental details in the ESI).在我們之前的研究中,已經(jīng)證明石墨烯之間的輕微的氧化還原反應(yīng)和氧化KMnO4會(huì)導(dǎo)致d-MnO2 納米片的高度活躍。在目前的工作,通過(guò)調(diào)整氧化石墨烯和高錳酸鉀的比例,可以讓不同含量的氧化石墨烯保留在d-MnO2 /氧化石墨烯復(fù)合材料。如圖1所示,我們通常試著三種不同的重量比率的高錳酸鉀和氧化石墨烯。兩個(gè)反應(yīng)物之間的氧化還原反應(yīng)導(dǎo)致三個(gè)前前驅(qū)體,P-MNP,P-MGC2 P-MGC1。通過(guò)在500氬氣中進(jìn)一步煅燒 ,由于氧化石墨烯熱解可以生成還原氣體CO,所以d-MnO2的前體(P-MGC

25、2和P-MGC1)可以還原為MnO.導(dǎo)致MGC2和MGC1的形成。無(wú)氧化石墨烯在P-MNP中發(fā)現(xiàn)，所以，在500氬氣中煅燒下，d-MnO2被轉(zhuǎn)移到 - MnO2納米粒子（記為MNP）。圖1所示的是這些錳氧化物和石墨烯的合成及其雜交的一般過(guò)程（更多的實(shí)驗(yàn)細(xì)節(jié)請(qǐng)參閱ESI）View Article OnlinePaperResults and discussion結(jié)果與討論The precursors resulting from the redox reaction between graphene oxide and KMnO4 were found to contain d-MnO2 wit

26、h a monoclinic birnessite (containing K) phase from the XRD (Fig. SI1, ESI), similar to our reported results. And the TGA results in air (Fig. SI2ac, ESI) showed that no graphene oxide remained in P-MNP, while for P-MGC2 and P-MGC1, it can be implied that the remaining graphene oxide contents were a

27、bout 14% and 37%, respectively, by calculating the mass loss during heating in air. After annealing these precursors at 500 C for 90 min under an Ar atmosphere, dierent manganese oxides were obtained. Fig. 2 shows the XRD patterns of MGC1, MGC2 and MNP. It is obvious that MNP (Fig. 2c) is indexed to

28、 a pure -MnO2 phase with a tetragonal crystal system (JCPDS no. 44-0141), while MGC2 (Fig. 2b) and MGC1 (Fig. 2a) readily correspond to a cubic phase of MnO (JCPDS no. 07-0230), and their TGA analysis in air indicates that rGO contents are about 18% and 39%, respectively (Fig. SI2df, ESI).與我們的報(bào)告結(jié)果相似

29、，從氧化石墨烯和高錳酸鉀氧化還原反應(yīng)產(chǎn)生的前體發(fā)現(xiàn)含有d-MnO2與水鈉錳礦單斜晶系（含鉀）從XRD相（圖1，ESI）。用熱量分析法分析空氣（圖si2aC，ESI）表明， 在P-MNP沒(méi)有氧化石墨烯，而P-MGC2 和P-MGC1，可以暗含著氧化石墨烯的含量分別為約14%和37%，計(jì)算在空氣中加熱質(zhì)量損失。這些前驅(qū)體退火后在500Ar氣流下90分鐘，獲得了不同錳氧化物。圖2顯示了MGC1, MGC2 和 MNP的X射線衍射曲線。很明顯，MNP（圖2c）是由一個(gè)四方晶系的純 - MnO2相，而MGC2（圖2b）和MGC1（圖2a）符合立方相的MnO，對(duì)它們?cè)诳諝庵羞M(jìn)行熱重量分析表明所含的氧化石墨

30、烯分別約18%和39%，（圖SI2dF，ESI）。The high-resolution X-ray photoelectron spectroscopy (XPS) analysis is shown in Fig. 3a. The peaks at around 640 and 651 eV for MGC2 and MGC1 are attrib uted to Mn(II) 2p3/2 and 2p1/2, respectively,37 which are quite different from the peaks for MNP located at about 642 and

31、653 eV, the characteristics of Mn(IV).38 Raman spectra were obtained to further identify the structure and constituent of MNP, MGC2 and MGC1, as presented in Fig. 3b. The characteristic D band and G band of carbon materials are present in MGC2 and MGC1, but absent in MNP, further indicating that the

32、re is no graphene in MNP. Addi-tionally, the peaks at around 580 and 650 cm 1 for MGC2 are assigned to manganese oxide.3941 In the sample MGC1, there is only one peak around 650 cm 1 for MnO, which may be due to the fact that the signal intensity for the metaloxygen bond is usually lower than that o

33、f the D and G bands for rGO. And in MGC1, the graphene content is higher than that in MGC2, so that the D and G peak intensities are even much higher than that for the metaloxygen bond. As a result, the peak at 580 cm 1 is not as obvious as that at 650 cm 1 in MGC1.高分辨率X射線光電子能譜（XPS）分析如圖3a所示。在640和651

34、 ev下MGC2 和 MGC1 的頂峰將屬性造成Mn（II）分別為2p3 / 2和2P1 / 2，這是完全不同于大約在642和653 eV MNP的頂峰峰位于Mn(IV)的特點(diǎn)，用拉曼光譜進(jìn)一步識(shí)別得到MNP ,MGC2 和MGC1的結(jié)構(gòu)和組成，如圖3b給出。特征D帶和G帶碳材料，出現(xiàn)在MGC2 和MGC1，但沒(méi)有在MNP，進(jìn)一步表明在MNP沒(méi)有石墨烯。在此基礎(chǔ)上，峰值在580和650cm-1 MGC2被分配到氧化錳。樣品中的MGC1，只存在一個(gè)峰值約650cm-1MnO，這可能是由于對(duì)金屬氧鍵的信號(hào)強(qiáng)度通常低于該D和G帶氧化石墨烯。在MGC1，石墨烯的含量高于MGC2，所以D和G的峰值強(qiáng)度甚

35、至高于金屬氧鍵。因此，在MGC1中580cm-1的峰值不如在650cm-1的明顯。Fig. 4, 5 and 6 show the typical SEM and TEM images of MNP, MGC2 and MGC1, respectively. Evidently, -MnO2 nano-particles in MNP are dispersed well with the size of about 50 nm with a narrow size distribution (Fig. 4a and c). For MGC2 and MGC1 as shown in Fig.

36、 5 and 6, MnO nanoparticles are both with a size of ca. 50 nm, and it is also obvious to note that the graphene content in MGC2 is lower than that in MGC1, which leads to more aggregation of MnO in MGC2 while MnO nano-particles in MGC1 are dispersed well on the surface of rGO. The high-resolution TE

37、M (HRTEM) images of MGC2 (Fig. 5d) and MGC1 (Fig. 6d) show the interplanar distance of ca. 0.25 nm, corresponding to the (111) plane of cubic MnO. The FFT (Fast Fourier Transform) patterns in the inset in the HRTEM images also show the spot pattern representative of the crystalline phase, although t

38、he intensity is quite low due to the low crys-tallinity of MnO nanoparticles. However, MNP showed a dierent lattice spacing of ca. 0.48 nm (Fig. 4d), which corre-sponds to the (200) plane of -MnO2. The N2 adsorption desorption isotherms (see Fig. SI3, ESI) also showed a higher BET specific surface a

39、rea of MGC1 (46.3 m2 g 1) than that of MGC2 (27.4 m2 g 1)圖4，5和6分別顯示MNP，MGC2 和 MGC1的典型標(biāo)準(zhǔn)電子組件。顯然，MNP中的 - MnO2納米顆粒在分散粒度分布窄的大小約為50 nm（圖4a和c）。對(duì)于MGC2和MGC1如圖5和6所示，MnO納米顆粒大小都約為50 nm，在MGC2中石墨烯的含量名顯低于MGC1，導(dǎo)致MGC2中更多的MnO納米顆粒聚集而MGC1中的MnO分散在氧化石墨烯表面。MGC2的高分辨透射電鏡（HRTEM）圖像（圖5d）和MGC1的（圖6d）顯示面立方MnO的晶面間距約為0.25nm。FFT（快速

40、傅里葉變換）在高分辨透射電子顯微鏡圖像在嵌入模式也表明結(jié)晶相的點(diǎn)模式的代表，雖然低結(jié)晶度的納米MnO的強(qiáng)度很低。然而，MNP顯示不同的晶格間距約0.48 nm（圖4d），其對(duì)應(yīng)的平面 - MnO2。N2吸附脫附等溫線（見(jiàn)圖SI3）也表現(xiàn)出MGC1（46.3 m2 g -1的BET特定表面積高于MGC2（27.4m2 g -1)The energy-dispersive spectra (EDS) also indicate the exis-tence of Mn, O and C in MGC1 and MGC2. The rough atom ratio of Mn to O is abo

41、ut 1 : 1 and the atom ratios of C to Mn are also consistent with the previous analysis. For MNP, the rough atom ratio of Mn to O is about 1 : 2 and the little signal (about 1.5 atom%) for carbon may come from the environment or adsorbed CO2. From the above analysis, by increasing the initial ratio o

42、f graphene oxide to KMnO4 in the redox reaction, the more graphene oxide can be remained in the resulting -MnO2/ GO composites (pure d-MnO2, i.e. P-MNP was obtained when the weight ratio of KMnO4 to GO was 4 : 1). During further heating treatment under an Ar atmosphere, the carbon in graphene skelet

43、on cannot reduce MnO2 since the temperature is only 500 C.42 The remaining graphene oxide undergoes thermolysis to release CO and CO2, as reported by many researchers.34,35 Thus, even in the inert atmosphere, MnO2 can be reduced to MnO, which is decorated on the graphene support and the remaining gr

44、aphene oxide is also reduced to rGO at the same time. This is quite different from results reported by Sun et al.,31 where Mn2+ was used as the Mn source and H2/Ar was used as the reductive gas for graphene oxide. For P-MNP, the absence of graphene oxide means the absence of CO release, so a-MnO2 na

45、noparticles were obtained because of the phase change of d-MnO2 into a-MnO2 during high-temperature treatment. In summary, in this work, the reducing power of graphene oxide has been successfully proven and used to prepare MnO from MnO2 without any extra reductants.能量色散譜（EDS）也表明MGC1 和 MGC2中存在錳，氧和碳 。

46、錳和氧的原子比率為11，碳和錳的原子比率還有待分析，。MNP，Mn 和O粗略的原子比率約為1：2，小的誤差（約1.5原子%）碳可能來(lái)自環(huán)境或吸附CO2。從以上的分析中，通過(guò)增加氧化石墨烯和高錳酸鉀在氧化還原反應(yīng)的初始比，氧化石墨烯更多的可以保持在產(chǎn)生的d-MnO2 /石墨復(fù)合材料（純-mno2，當(dāng)KMnO4和石墨烯的重量比為41可以得到P- MNP）。在進(jìn)一步加熱處理氬氣下，,由于溫度只有500，所以石墨烯的碳骨架不能減少M(fèi)nO2,根據(jù)很多研究人員的報(bào)告，剩余的氧化石墨烯進(jìn)行熱解釋放CO和CO2。因此，即使在惰性氣體中，MnO2可以還原成MnO，裝飾支持作用的石墨烯和剩余的石墨烯同時(shí)轉(zhuǎn)化為氧化

47、石墨烯。這和Sun等人報(bào)道結(jié)果有很大的不同，Mn2+作為錳源，氫氣/氬氣作為氧化石墨烯的還原氣體。對(duì)于P-MNP，氧化石墨烯的缺乏意味著CO釋放的情況下，由于相變?yōu)楦邷靥幚?MnO2， - MnO2得到 - MnO2納米顆粒。總之，在這項(xiàng)工作中，總之,在這個(gè)工作中,氧化石墨烯的還原能力已經(jīng)成功地證明,用于準(zhǔn)備MnO沒(méi)有用任何額外的還原劑。 The electrochemical lithium-storage performance of the as-prepared MnO/rGO composites was also investigated. The galvanostatic di

48、scharge/charge cycling performance was tested at a current of 100 mA g 1 with a voltage window of 0.053.5 V. As shown in Fig. 7a, for a current density of 100 mA g 1, the first discharge capacity of MGC1 was over 1800 mA h g 1, and the initial capacity loss is about 50%, which is believed due to the

49、 disordered rGO and the trap sites for Li on its surface to form SEI. Interestingly, in the following cycling, the capacity increased gradually and stabilized at 900 mA h g-1 after 85 cycles. The capacity rise has been reported in many published studies and was considered to be attributed to a possi

50、ble activation process in the electrode.31,33 The initial capacity has a significant irreversible component; however, capacity in subsequent cycles is of similar order to that expected for Mn2+/ Mn0 conversion. On a number of cycles, the capacity exceeded than that expected for just the Mn couple an

51、d may possibly reflect a component due to the organic polymeric/gel like films formed reversibly by decomposition at low potential., According to the theoretical overall reaction between lithium and graphene nanosheets, 2C + Li+ + e- LiC2 (with a capacity of 1116 mA h g 1)4446 and the theoretical co

52、nversion of MnO and Li, MnO + 2Li+ + 2e-Li2O + Mn (with a capacity of 756 mA h g 1),47 as well as the content analysis of the composite through TGA shown in Fig. SI2df, the theoretical capacity for MGC1 is about 896 mA h g 1, which is in good agreement with the stable capacity of 900 mA h g 1 after

53、85 cycles at a low current density of 100 mA g -1.對(duì)所制備的二氧化錳/石墨烯復(fù)合物的電化學(xué)儲(chǔ)鋰性能進(jìn)行了研究。在電流100mAg-1與電壓0.053.5 V下，測(cè)試恒電流充/放電的循環(huán)性能，在電流密度為100mAg-1，MGC1首次放電容量超過(guò)1800 mA h g -1，初始容量損失約50%，這被認(rèn)為是由于無(wú)序的氧化石墨烯和陷阱的網(wǎng)站里在其表面形成SEI。有趣的是，在以下循環(huán)中，在循環(huán)85次后，容量逐漸增加并穩(wěn)定在900mA h g -1。在許多已發(fā)表的研究報(bào)告中認(rèn)為，能力的上升，可能是由于電極中的一個(gè)激活過(guò)程。初始容量有顯著的不可逆的成分；

54、然而，在隨后的循環(huán)中，預(yù)計(jì)Mn2+ / Mn0轉(zhuǎn)換是類似的命令。在一個(gè)周期數(shù)，容量超過(guò)了預(yù)期只是Mn結(jié)合和可能反映組件，由于有機(jī)高分子/凝膠薄膜在低電位可以被分解， 根據(jù)鋰和石墨烯之間的理論總反應(yīng)，2C + Li+ + e- LiC2（容量為1116mAg-1）,以及MnO和Li的理論轉(zhuǎn)換，MnO + 2Li+ + 2e-Li2O + Mn （容量為756 mA h g-1）、通過(guò)熱重量分析法對(duì)復(fù)合材料的內(nèi)容進(jìn)行分析，MGC1的理論容量是896mAhg-1，這與900 mA h g-1在100 mAg-1低電流密度下循環(huán)85次 后的穩(wěn)定容量一致。View Article OnlinePaper

55、 In the following rate capability test at various current densities, discharge capacities of 750 mA h g -1, 580 mA h g 1, 400 mA h g 1 and 160 mA h g 1 were retained at current densities of 200 mA g 1, 400 mA g -1, 800 mA g 1 and 1.6 A g 1, respectively. It seems that the rate performance is not as

56、high as that of other reported carbonMnO materials.31,33 For the MnO/ graphene prepared by Sun et al., the reversible capacity is high up to 2014.1 mA h g 1 at a current of 200 mA g 1 and 625.8 mA h g 1 at a current of 3000 mA g 1.31 Also according to Li et al., the MnOC electrode delivered a capaci

57、ty of 861 mA h g 1 at a current of 100 mA g 1 and 462 mA h g 1 at a current of 2000 mA g 1.33 The relatively low rate capability may be ascribed to the relatively low electronic conductivity of reduced graphene oxide in the active material that results in the incomplete discharge/ charge process at

58、high current densities. However, importantly, the capacity was able to recover to more than 900 mA h g -1 after 120 cycles when the current density was returned to 100 mA g 1. More details of the discharge/charge process can be seen from the discharge/charge voltage profile in Fig. 7b, which shows a discharge plateau at ca. 0.31 V in the 1st cycling and a shifted plateau at ca. 0.42 V in the later cycling. It a