Carbon Composite Anode for Potassium-Ion Batteries

Subscriber access provided by Kaohsiung Medical University

Article

Phosphorus/carbon composite anode for potassium-ion batteries: insights into high initial Coulombic efficiency and superior cyclic performance Xingkang Huang, Dan Liu, Xiaoru Guo, Xiaoyu Sui, Deyang Qu, and Junhong Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03241 • Publication Date (Web): 22 Oct 2018 Downloaded from http://pubs.acs.org on October 23, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Phosphorus/carbon composite anode for potassium-ion batteries: insights into high initial Coulombic efficiency and superior cyclic performance Xingkang Huang,† Dan Liu,† Xiaoru Guo, Xiaoyu Sui, Deyang Qu, and Junhong Chen* Department of Mechanical Engineering, University of Wisconsin-Milwaukee, 3200 North Cramer Street, Milwaukee, WI, 53211, USA. *Email: [email protected].

Abstract: Potassium-ion batteries recently start to attract attention because potassium is abundant in the Earth’s crust and the commercial graphite anode works well in potassium-ion batteries. However, the relatively low theoretical capacity of the graphite (279 mAh g-1) may limit the future application of potassiumion batteries. Here we report a phosphorus (P)/activated carbon (AC) composite prepared by a vaporization-condensation-conversion approach. While the higher P loadings result in greater capacities of the P/AC composites, the relatively lower P loadings lead to superior cyclic performance; for example, the P/AC composite with 45 wt.% of P (named PAC-50) delivered a maximum capacity of 430 mAh g-1

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 32

while the one with 32 wt.% of P (named PAC-35) exhibited 70% capacity retention after 500 cycles. More importantly, by controlling the P content the initial Coulombic efficiency (ICE) can be optimized, reaching the highest value of 84% when the P content is 45 wt.% (named PAC-50). The decreased surface area and the reduced oxygen-containing groups account for the high ICEs.

Keywords: potassium-ion battery, phosphorus, initial Coulombic efficiency, cyclic performance

2 ACS Paragon Plus Environment

Page 3 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION

Lithium-ion batteries have achieved successful applications in energy storage systems; however, the limited lithium resource will be a critical problem upon the growing market of electric vehicles.1 Potassium-ion and sodium-ion batteries, as alternatives to lithiumion batteries, start to attract attentions due to the abundancy of potassium and sodium in the Earth’s crust. The commercial graphite anodes for lithium-ion batteries do not work in sodium-ion batteries because of the energetic instability of the Na-graphite intercalation compounds,2-4 but do work in potassium-ion batteries,5-7 showing a maximum capacity of 250 mAh g-1 with an initial Coulombic efficiency (ICE) of 89%.6 This phenomenon extremely elevates application potential of potassium-ion batteries. However, due to the limited theoretical capacity of graphite (279 mAh g-1), other anode candidates have been investigated, such as graphene-based materials,8-11 sulfides,12-15 and phosphorus (P).1618

Graphene-based materials was reported with capacities of 326-567 mAh g-1 at 50 mA

g-1 while sulfides showed capacities of 355-679 mAh g-1 at 20-25 mA g-1.13-15 However, these anode materials with high capacities usually feature a low initial Coulombic

ACS Paragon Plus Environment

3


Page 4 of 32

efficiency, which will result in the irreversible consumption of potassium ions supplied by the cathode material in full cells. P possesses a high theoretical capacity of 843 mAh g-1, forming KP upon potassiation. A black P/graphite composite was prepared using a ball-milling method, showing a capacity of 443 mAh g-1, with a capacity retention of 61% after 50 cycles and an initial Coulombic efficiency of 60%, when the weight ratio of P/graphite is 1:1.16 Very recently, Wu et al. directly used red P instead of black P to ball mill with graphite; the resulting P/graphite delivered a capacity of 483 mAh g-1 and retained 67% of the capacity after 50 cycles.18 The high capacity of the two studies on P/graphite composites indicates very promising potential of phosphorus as anode materials for potassium-ion batteries; however, the cyclic performance of these anode materials needs to be improved, and the low initial Coulombic efficiencies (50-61%) also needs to be addressed. Thus, in this study, we loaded red phosphorus into micropores of activated carbon (AC) through a vaporization-condensation-conversion approach, forming P/AC composites as anodes for potassium-ion batteries, in which the micropores of the AC provide void spaces for loading P and volume expansion upon potassiation. Compared with ball milling


4

Page 5 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


to form P/C composites,16,

18

vaporization-condensation-conversion method can

homogenously implant P into micropores of the AC while leaving void spaces for volume expansion during potassiation. This method has been successfully used to synthesize P/C composites for lithium-ion and sodium-ion batteries,19 but has not been reported for potassium-ion batteries until now, which is likely due to the much lower theoretical capacity of P in potassium-ion batteries (843 mAh g-1 vs. 2,596 mAh g-1 for lithium-ion and sodium-ion batteries). In addition, because of larger cation radius of K+, compared with Li+ and Na+, the volume expansion upon potassiation is greater. As a result, design criteria of P/C composites for lithium-ion and sodium-ion batteries are unsuitable for potassium-ion batteries. Therefore, the content of P in the P/AC composite needs to be rationally tuned for potassium-ion batteries to achieve a high capacity and a high ICE with superior cyclic performance. More importantly, we reveal the relation between the P content and the capacity, ICE, and cyclic performance.

EXPERIMENTAL


5


Page 6 of 32

Commercial activated carbon (AC; YP50F, Kurary Chemical Manufacturer) was used to load red P (Millipore-Sigma). The AC was heated at 300 C for 4 h under vacuum and stored in a glovebox before use. The red P was purified by boiling it in deionized (DI) water and was transferred into the glovebox prior to use. P and AC were loaded into a single-ended glass tube and sealed after being purged three times with Ar gas. The sealed tube was heated at 550 C for 2 h, cooled down to 260 C and maintained at 260 C for 24 h. Note that red P sublimes at 416 C; therefore, 550 C was chosen as the evaporation temperature because the melting temperature of the Pyrex glass tube used is approximately 600 C. After adsorption of P into AC during cooling down, the P is in a form of white P that can spontaneously ignite at room temperatures, which can be prevented by converting it to red P after annealing at 260 C for 24 h. The resulting P/AC composite was washed by carbon disulfide and dried under vacuum. To reveal the relation of the P content and the capacity, ICE, and cyclic performance, P/AC composites with P contents of 20, 30, 35, 40, 42, 45, 47, 50, and 60 wt.% were designed, denoting PAC-20, PAC-30, PAC-35, PAC-40, PAC-42, PAC-45, PAC-47, PAC50, and PAC-60, respectively.


6

Page 7 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The morphologies of the as-prepared samples were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), performed on a Hitachi S-4800 SEM machine equipped with a Bruker EDS detector. Transmission electron microscopy (TEM) was carried out on a Hitachi H-9000-NAR machine operating at an acceleration voltage of 300 kV. Powder X-ray diffraction (XRD) was performed on a Bruker D8 DISCOVER diffractometer with Cu K radiation. The surface area measurements were carried out by Brunauer, Emmett, and Teller (BET) N2 adsorption/desorption on a Micromeritics ASAP 2020. Pore size was analyzed based on a quenched solid density functional theory (QSDFT) kernel applied to the adsorption branch using a slit pore model. X-ray photoelectron spectroscopy (XPS) spectra of samples were obtained using a PerkinElmer PHI 5440 ESCA spectrometer with monochromatic Mg Kα radiation as the X-ray source. Thermogravimetric/ differential thermal analysis (TG/DTA) was carried out under air flow (100 mL min-1) at a heating rate of 10 C min-1 on a SDT 2660 Simultaneous DSC-TGA instrument. Preparation of Electrodes and Coin Cells. The charge/discharge performance was characterized by using 2032-type coin cells that were assembled in an argon-filled glove


7


Page 8 of 32

box, with oxygen and moisture content below 1 ppm. Electrodes were prepared by mixing the as-prepared materials as the active material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and carbon black as a conductor with a weight ratio of 80:5:5:10 to form a slurry. The resulting slurries were coated onto a Cu foil (12-m in thickness) current collector using the doctor blade method. After drying and pressing, the Cu foil was cut into disks (1.1 cm in diameter) with typical electrode material loadings of ca. 1-1.5 mg cm-2. Then, 0.5 M KPF6 dissolved in ethylene carbonate/propylene carbonate (1:1, v/v) was used as the electrolyte. The coin cells were tested on a LAND battery tester with a cut-off voltage range between 0.01 and 3 V. The current densities and capacities were calculated based on the total mass of P/AC composites loaded on the electrodes. Note that the potassiation behavior was defined as “charge” because the P is an anode material. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the as-prepared anode were measured on a PARSTAT 4000 electrochemical station using a three-electrode cell, with the P/AC composite electrode as the working electrode, a sodium disk as the counter electrode, and a potassium arc as the reference electrode. CV was carried out at a


8

Page 9 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


scanning rate of 0.05 mV s-1 while EIS was tested between 10,000-0.1 Hz with an amplitude of 10 mV.

RESULTS AND DISCUSSION

Graphite has been proven to deliver a reversible capacity of approximately 244 mAh g-1 as an anode for potassium-ion batteries;6 in contrast, activated carbon (AC) only can discharge (depotassiate) a capacity of approximately 50 mAh g-1 as shown in Figure 1. However, AC possesses a high surface area with rich micropores, which leads to an excellent matrix to load P, alleviating volume expansion of P upon patassiation and thereby addressing the poor cyclic performance of the red P. Thus, the combination of advantages of the AC and the red P can potentially result in P/AC composites with a high capacity, a high initial Coulombic efficiency, and superior cyclic performance. When the red P was heated up to 550 C, it sublimed to P vapor that was adsorbed into the micropores in the AC during cooling down to 260 C. The pore volume of the AC was measured to be 0.78 cm3 g-1 by N2 adsorption/desorption, which allows for a maximum P


9


Page 10 of 32

loading of 1.42 g per gram of the AC, corresponding to 60 wt.% of P in the P/AC composite. Therefore, 20-60 wt.% of P was intended to be loaded into the AC, forming composites to optimize the electrochemical performance of the P/AC composites. Note that the P contents in the P/AC composites were observed always lower than their designed values; for example, the P contents in PAC-20, PAC-30, PAC-35, PAC-40, PAC-42, PAC-45, PAC-47, PAC-50, and PAC-60 were measured as 17, 26, 32, 37, 40, 43, 44, 45, and 53 wt.%, respectively (Figure S1). The main reason for the slightly lower P contents in the as-obtained P/AC composites is the possible existence of white P residual that was washed out by carbon disulfide. As shown in Figure 1b and c, when P content is lower than 26 wt.% (PAC-30), no significant initial capacity increased while the capacity enhanced almost linearly when P contents were higher than 32 wt.% (PAC-35) in the P/AC composites (Figure 1d). A maximum discharge capacity of 430 mAh g-1, based on the total P/AC composite mass loaded on the electrode, was achieved with the P content of 45 wt.% (PAC-50), beyond which the capacity decreased because overdosing P in the AC resulted in formation of P particles. According to the t-plot analysis, the micropore volume was 0.626 cm3 g-1, which


10

Page 11 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


allows for the maximum amount of 53 wt.% of P filling into the micropores of the AC. In other words, when micropores of the AC were fully loaded, the P vapor started to deposit on the exterior surface of the AC, leading to the formation of elemental P particles.

Figure 1. (a) Coulombic efficiency, (b) cyclic performance, (c) charge/discharge curves of the first cycle, (d) relation between specific surface area, capacity, initial Coulombic efficiency and the P content of the P/AC composites, and (e) long-term cycling


11


Page 12 of 32

performance of PAC-35 and PAC-40. Note that two points were skipped every three cycles in (a,b) to exhibit the figures more clearly.

The capacities of 400-430 mAh g-1 for P/AC composites with P contents of 37-53 wt.% are close to those of the black P/graphite composites reported by Sultana et al. (443 mAh g-1 for the P/graphite with P/C ratio of 1)

16

and Wu et al. (482.9 mAh g-1).18 They both

used the ball-milling method to prepare black P/graphite composites. In contrast, we used the vaporization-condensation-conversion approach to implant red P into microporous AC. More importantly, our P/AC composites exhibit high ICEs up to 84.5%, much greater than those black P/graphite composites (50.3-67%).16, 18 Actually, most of carbon- and phosphorus-based anodes for potassium-ion batteries were reported to show an ICE of 17-67%,5,

7, 16-18, 20-23

with only one reported to be 89% for a graphite anode,6 as

summarized in Table S1.

ICE is extremely important in full cells because a low ICE of an anode will lead to a high “dead” cathode ratio after the initial cycle; for example, if an anode possesses an ICE of


12

Page 13 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60%, at least 40% of potassium ion will not be retained by the cathode after first charge since the full cell capacity is typically limited by the cathode. As shown in Figure 1a, the ICE of the AC was as low as 16%, which is comparable with that of a nitrogen-doped porous carbon (17%)22 and a nitrogen/oxygen dual-doped hard carbon (25%)20. The ICEs increased to 20%, 29%, 41%, and 53% for PAC-20, PAC-30, PAC-35, PAC-40, respectively. When P content was higher than 37 wt.% (PAC-40), the ICE enhanced dramatically to 62, 67, 75, and 84% for the PAC-42, PAC-45, PAC-47, and PAC-50, respectively. In contrast, the PAC-60 showed an ICE of 81%, lower than that of the PAC50, which is due to the formation of individual P particles on the AC surfaces because of overdosing P in the case of PAC-60 (see below). Because of large volume expansion upon potassiation, the P that was not filled in the pores of the AC may pulverize and lose electrical contact with the current collector, thereby decreasing the ICE. The low ICEs of the P/AC composites with low P contents were apparently related to the high surface area. The surface area of the AC is as high as 1,677 m2 g-1, which decreases to 1,067, 636, 381, 104, 41, 36, 18, 3.6, and 2.7 m2 g-1 for PAC-20, PAC-30, PAC-35, PAC-40, PAC-42, PAC-45, PAC-47, PAC-50, and PAC-60, respectively. As


13


Page 14 of 32

shown in Figure 1d, the relation between the increase of ICE and the decrease of surface area is not linear; instead, a nearly logarithmical relation between them was observed (Figure S2). The deviation from the linear relation suggests the irreversible initial capacity can not be attributed to the solid electrolyte interphase (SEI) alone. By comparing the first and the second charging curves (Figures 1c and S3), we can see most of the irreversible capacity was from the capacity located above 0.5 V, with a voltage plateau at approximately 1.23 V. The decomposition of the carbonate electrolytes and formation of the SEI layer typically occur below 1.0 V; for example, the SEI formation was reported at 0.8 V on graphite electrodes.24 Thus, the charge (potassiation) capacity located above 1.0 V could be related to the reduction of oxygen containing groups; for example, carboxyl groups (C=O) can be irreversibly reduced to C-O-K. XPS analysis indicates oxygen content on the AC surface is approximately 17.5 at.% in the form of C-O, C=O, and OC=O (Figure S4). In contrast, the C1s peak for O-C=O bond is barely observed when the P content reaches 40 wt.% (e.g., PAC-42 and PAC-47 as shown in Figure S4). In addition, the O content on the PAC-20 surface is 12.9 at.% and the atomic ratio of O/P decreases from 4.78 for PAC-20 to 0.96 for PAC-50.


14

Page 15 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) XPS P 2p spectra, (b) XRD patterns, (c) isothermal curves, and (d) pore size of P/AC composites with various P contents.

Figure 2a shows the XPS peaks of P 2p for the P/AC composites. When the P contents are low in the P/AC composite, the main peak was located at ~130 eV, accompanied by an additional peak at ~133 eV, which are assigned to elemental P and P-O-C, respectively. The existence of the P-O-C bond was reported in mechanically ball-milled


15


Page 16 of 32

P/graphite18 and P/carbon nanotube25 composites. Here we confirmed the formation of P-O-C on the surface of our P/AC composites. The P 2p XPS peaks were fitted by assigning the peaks at 129.990.11 and 130.870.12 eV to P 2p3/2 and P 2p1/2 while the peaks at 132.540.21 and 133.400.21 to P-O-C 2p3/2 and P-O-C 2p1/2, respectively. No phosphorus oxide (P2O5) was detected at 135.2-135.6 eV.26-27 With the increasing P loading, the P-O-C content decreased, which suggests the P-O-C was formed on the surface of the AC. Therefore, the oxygen-containing groups (such as carboxyl) on the AC surface were reduced by the P vapor at elevated temperatures, as evidenced by the disappearance of XPS C1s peak for O-C=O (Figure S4). The P vapor then deposited on the P-O-C surface during the cooling process, which facilitates the uniform deposition of P into pores of the AC. When the P contents are low in the P/AC composites, the P layers are thin, so that the P-O-C layers are detectable by the XPS; in contrast, when the P contents are higher than 44 wt.% (PAC-47), the P layers are thick enough, resulting in undetectable P-O-C (Figure 2a). The formation of P-O-C on the AC surface during synthesis avoids the irreversible reduction of oxygen-containing groups (such as C=O) upon potassiation; therefore, when


16

Page 17 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the P content in P/AC composites is higher than 26 wt.% (PAC-30), the voltage plateau related to reduction of oxygen-containing groups disappeared (Figure 1c), and the ICE increased dramatically along with the increasing P content (Figure 1d). When P loadings are high in the P/AC composites (e.g., PAC-60), only red P can be detected by XRD (Figure 2b); the characteristic peaks at ~25  and 44  for the AC were not detectable, which suggests the thick P layers cover on the AC surface and is consistent with the XPS analysis. Note that a very broad peak between 10-30  was observed for the pristine AC, which resulted from the overlap of uniform micropores and the 002 facet of the AC. As a matter of fact, the pore size of the AC was shown with a sharp peak at 0.73 nm from the N2 adsorption/desorption analysis (Figure 2c and d), which can lead to the XRD peak at ~13  in 2 theta (corresponding to d-spacing of ~0.7 nm). Upon loading P into micropores of the AC, the XRD peak at ~13  decreased dramatically (Figure 2b), which agrees well with the decreasing amount of micropores (Figure 2d). When the P contents are higher than 37 wt.% (PAC-40), the microporous characteristic of the AC disappeared, showing a surface area lower than 104 m2 g-1 and an ICE higher than 51%. The very weak XRD peaks suggest the as-prepared P/AC


17


Page 18 of 32

composites are poorly crystallized, which was confirmed by TEM observation. As shown in Figure S5, only very weak rings that belong to carbon were observed, and some shortdistance-ordered lattices of P and C indicate P was impregnated in C. The disappearance of micropores of the AC upon the increasing P loading was also observed by SEM (Figure 3). The pristine AC possesses typical particle sizes of 6-10 m (Figure 3a), with micropores as indicated by the surface observation (Figure 3b). Upon loading P lower than 37 wt.% (PAC-40) into the AC, the P/AC composites retained similar morphology (Figure 3c,d). When the P content in the P/C composite reached 44 wt.% (PAC-47), the micropores on the AC surface were almost filled up by the P (Figure 3e); in contrast, implanting 45 wt.% of P into the AC (PAC-50) resulted in complete coverage of the micropores of the AC, showing much smoother surface compared with PAC-47 (Figure 3f). Further increase of P content to 53 wt.% (PAC-60) led to formation of P particles on the AC surface (Figure 3g,h and Figure S6), which explains the lower capacity and ICE of PAC-60 compared with those of PAC-50 (Figure 1). Therefore, the dosages of P in the P/AC composites should be limited within 45 wt.% (PAC-50) to prevent the AC from being overdosed. An individual particle of PAC-50 was analyzed using energy


18

Page 19 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dispersive X-ray spectroscopy (EDS), suggesting uniform distribution of the P in the AC matrix (Figure 3i-k). EDS elemental analysis indicates the P content is approximately 48 wt.% (Figure 3l), close to the designed value (i.e., 50 wt.%) and the TGA result (45 wt.%).

Figure 3. SEM images of (a,b) AC, (c,d) PAC-40, (e) PAC-47, (f) PAC-50, and (g,h) PAC60. (i-l) SEM image and EDS analysis of PAC-50, in which Cu was detected because a Cu foil tape was used to exclude the interference of double-sided carbon tape on the C analysis.


19


Page 20 of 32

CV was used to investigate the irreversible capacities. As shown in Figure 4, the pristine AC possesses an irreversible cathodic peak at 1.23 V, related to the reduction of oxygencontaining groups on the AC surfaces, which is consistent with the initial potassiation behavior of the AC (Figure 1c). This peak was not shown after loading P because the oxygen-containing groups were reduced by the P at the elevated temperatures. In contrast, a shoulder peak was observed at ~0.45 V (Figure 4b), which is ascribed to the SEI formation because this peak was not shown during the second and the third cycles (Figure S7). Note also that this peak is difficult to observe when the P loadings are high in the P/AC composites because K+ starts to insert into the P above 0.45 V. As an evidence, a reversible cathodic peak was observed at ~0.54 V for the PAC-50 after the initial cycle (Figure S7).


20

Page 21 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. CV curves of P/AC composites with various P contents, in which (b) is the zoomed-in plot from (a) to show the peaks clearly.

Besides ICE, the cyclic performances of the P/AC composites are also significantly affected by the P content (Figure 1c). With P contents lower than 40 wt.% (PAC-42), the P/AC composites display excellent cyclic performance; for example, the PAC-40 delivered a reversible capacity of 170 mAh g-1 and retained 142 mAh g-1 after 100 cycles. In contrast, higher P loadings resulted in higher capacities but poorer cyclic performance due to the large volume expansion upon potassiation. The P/AC composites with 40-44 wt.% showed high capacities with relatively stable cyclic performance. Figure 1e depicts the long-term cyclic performance of the PAC-35 and PAC-40, showing 70% capacity retention after 500 cycles and 53% capacity retention after 400 cycles, respectively. Therefore, the relatively low P contents in P/AC composites may lead to excellent cyclic performance because of ample void spaces for accommodating volume expansion upon potassiation. In addition, when the P loading in the P/AC composite is relatively low, all the P is confined in the micropores and no P is coated on the external surface of the AC.


21


Page 22 of 32

This helps to build up a stable SEI layer on the AC external surface. In contrast, when the P contents in the P/AC composites are high enough, the P starts to deposit on the AC external surface. In this case, during repeated charging/discharging, the SEI layers on the P surface may crack and form again and again. The unsteady SEI layers thus lead to poor cyclic performance. Very recently, Yu et al.28 compared the sodium storage performance of two types of the red P/carbon composites, i.e., a P@AC composite with P confined within micropores of activated carbons and a P@CNT (carbon nanotube) composite with P deposited on the surface of CNTs. They found that using porous carbons can accommodate the volume changes of P within the porous structures as a whole and enable stable SEI and thus excellent electrochemical stability. On the contrary, the P@CNT composite displayed the inferior performance due to the unstable SEI and the resulting loss of electrical contact between CNTs and superficial P/NaxP. The P/AC composites are not expected to possess good rate capacity because of lack of long-range order in AC. For example, PAC-47 delivered 408, 313, 198, 126, 61 mAh g-1 at 50, 100, 200, 500 and 1,000 mA g-1 (Figure S8). This rate performance was consistent with the relatively large impedance (Figure S9). Quick depotassiation of P was


22

Page 23 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


observed while the alloying process of the P with potassium was slow.16 In other words, when charging at low current densities, P may achieve good discharge rate capability.

CONCLUSIONS

P/AC composites were synthesized through the vaporization-condensation-conversion method. P/AC composites with relatively high P contents offer high capacities (up to 430 mAh g-1) while relatively low P loadings in AC lead to excellent cyclic performance. More importantly, loading P into porous carbon can address the low ICE issue of porous carbon; for example, the highest ICE of 84% was achieved for PAC-50. Thus, our findings pave an avenue for engineering high-capacity anodes for potassium-ion batteries with a high ICE.

ASSOCIATED CONTENT

Supporting Information.


23


Page 24 of 32

The Supporting Information is available free of charge on the ACS Publications website.

Comparison of the performance of carbon- and phosphorus-based anodes for potassiumion batteries, TGA curves of the AC and the P/AC composites, relationship between ICE and surface area for the P/AC composites, charge/discharge curves of the P/AC composites at the second cycle, XPS spectra of the AC, PAC-42, and PAC-47, TEM analyses for PAC-47, SEM image of PAC-60 and its corresponding EDS analysis, CV curves of pristine AC and P/AC composites with various P contents, Rate performance of PC-47 and its corresponding charge/discharge curves at various current densities, and EIS of PAC47 at various states of charges (PDF).

AUTHOR INFORMATION

Corresponding Author *Email: [email protected].

Author Contributions

†These authors contributed equally.


24

Page 25 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACKNOWLEDGMENT JH Chen acknowledges support by (while serving at) the U.S. National Science Foundation.

REFERENCES 1. Nayak, P. K.; Yang, L. T.; Brehm, W.; Adelhelm, P. From Lithium-Ion to Sodium-Ion Batteries: Advantages, Challenges, and Surprises. Angew. Chem. Int. Ed. 2018, 57 (1), 102-120, DOI 10.1002/anie.201703772. 2. Nobuhara, K.; Nakayama, H.; Nose, M.; Nakanishi, S.; Iba, H. First-principles study of alkali metal-graphite intercalation compounds. J. Power Sources 2013, 243, 585-587, DOI 10.1016/j.jpowsour.2013.06.057. 3. Luo, W.; Wan, J. Y.; Ozdemir, B.; Bao, W. Z.; Chen, Y. N.; Dai, J. Q.; Lin, H.; Xu, Y.; Gu, F.; Barone, V.; Hu, L. B. Potassium Ion Batteries with Graphitic Materials. Nano Lett. 2015, 15 (11), 7671-7677, DOI 10.1021/acs.nanolett.5b03667.


25


Page 26 of 32

4. Liu, Y. Y.; Merinov, B. V.; Goddard, W. A. Origin of low sodium capacity in graphite and generally weak substrate binding of Na and Mg among alkali and alkaline earth metals. PNAS 2016, 113 (14), 3735-3739, DOI 10.1073/pnas.1602473113. 5. Jian, Z. L.; Luo, W.; Ji, X. L. Carbon Electrodes for K-Ion Batteries. J. Am. Chem.

Soc. 2015, 137 (36), 11566-11569, DOI 10.1021/jacs.5b06809. 6. Komaba, S.; Hasegawa, T.; Dahbi, M.; Kubota, K. Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors.

Electrochem.

Commun.

2015,

60,

172-175,

DOI

10.1016/j.elecom.2015.09.002. 7. Zhao, J.; Zou, X. X.; Zhu, Y. J.; Xu, Y. H.; Wang, C. S. Electrochemical Intercalation of Potassium into Graphite. Adv. Funct. Mater. 2016, 26 (44), 8103-8110, DOI 10.1002/adfm.201602248. 8. Ju, Z. C.; Zhang, S.; Xing, Z.; Zhuang, Q. C.; Qiang, Y. H.; Qian, Y. T. Direct Synthesis of Few-Layer F-Doped Graphene Foam and Its Lithium/Potassium Storage Properties.

ACS Appl. Mat. Interfaces 2016, 8 (32), 20682-20690, DOI 10.1021/acsami.6b04763.


26

Page 27 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9. Share, K.; Cohn, A. P.; Carter, R.; Rogers, B.; Pint, C. L. Role of Nitrogen-Doped Graphene for Improved High-Capacity Potassium Ion Battery Anodes. ACS Nano 2016,

10 (10), 9738-9744, DOI 10.1021/acsnano.6b05998. 10. Gong, S.; Wang, Q. Boron-Doped Graphene as a Promising Anode Material for Potassium-Ion Batteries with a Large Capacity, High Rate Performance, and Good Cycling

Stability.

J.

Phys.

Chem.

C

2017,

121

(44),

24418-24424,

DOI

10.1021/acs.jpcc.7b07583. 11. Ma, G. Y.; Huang, K. S.; Ma, J. S.; Ju, Z. C.; Xing, Z.; Zhuang, Q. C. Phosphorus and oxygen dual-doped graphene as superior anode material for room-temperature potassium-ion batteries. J. Mater. Chem. A 2017, 5 (17), 7854-7861, DOI 10.1039/c7ta01108c. 12. Ren, X. D.; Zhao, Q.; McCulloch, W. D.; Wu, Y. Y. MoS2 as a long-life host material for potassium ion intercalation. Nano Res 2017, 10 (4), 1313-1321, DOI 10.1007/s12274016-1419-9.


27


Page 28 of 32

13. Gao, H.; Zhou, T. F.; Zheng, Y.; Zhang, Q.; Liu, Y. Q.; Chen, J.; Liu, H. K.; Guo, Z. P. CoS Quantum Dot Nanoclusters for High-Energy Potassium-Ion Batteries. Adv. Funct.

Mater. 2017, 27 (43), 1702634, DOI 10.1002/Adfm.201702634. 14. Lakshmi, V.; Chen, Y.; Mikhaylov, A. A.; Medvedev, A. G.; Sultana, I.; Rahman, M. M.; Lev, O.; Prikhodchenko, P. V.; Glushenkov, A. M. Nanocrystalline SnS2 coated onto reduced graphene oxide: demonstrating the feasibility of a non-graphitic anode with sulfide chemistry for potassium-ion batteries. Chem. Commun. 2017, 53 (59), 8272-8275, DOI 10.1039/c7cc03998k. 15. Xie, K. Y.; Yuan, K.; Li, X.; Lu, W.; Shen, C.; Liang, C. L.; Vajtai, R.; Ajayan, P.; Wei, B. Q. Superior Potassium Ion Storage via Vertical MoS2 "Nano-Rose" with Expanded Interlayers on Graphene. Small 2017, 13 (42), 1701471, DOI 10.1002/Smll.201701471. 16. Sultana, I.; Rahman, M. M.; Ramireddy, T.; Chen, Y.; Glushenkov, A. M. High capacity potassium-ion battery anodes based on black phosphorus. J. Mater. Chem. A 2017, 5 (45), 23506-23512, DOI 10.1039/c7ta02483e.


28

Page 29 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17. Zhang, W. C.; Mao, J. F.; Li, S. A.; Chen, Z. X.; Guo, Z. P. Phosphorus-Based Alloy Materials for Advanced Potassium-Ion Battery Anode. J. Am. Chem. Soc. 2017, 139 (9), 3316-3319, DOI 10.1021/jacs.6b12185. 18. Wu, X.; Zhao, W.; Wang, H.; Qi, X.; Xing, Z.; Zhuang, Q.; Ju, Z. Enhanced capacity of chemically bonded phosphorus/carbon composite as an anode material for potassiumion

batteries.

J.

Power

Sources

378,

2018,

460-467,

DOI

10.1016/j.jpowsour.2017.12.077. 19. Li, W. H.; Yang, Z. Z.; Li, M. S.; Jiang, Y.; Wei, X.; Zhong, X. W.; Gu, L.; Yu, Y. Amorphous Red Phosphorus Embedded in Highly Ordered Mesoporous Carbon with Superior Lithium and Sodium Storage Capacity. Nano Lett. 2016, 16 (3), 1546-1553, DOI 10.1021/acs.nanolett.5b03903. 20. Yang, J. L.; Ju, Z. C.; Jiang, Y.; Xing, Z.; Xi, B. J.; Feng, J. K.; Xiong, S. L. Enhanced Capacity and Rate Capability of Nitrogen/Oxygen Dual-Doped Hard Carbon in Capacitive Potassium-Ion

Storage.

Adv.

Mater.

2018,

30

(4),

1700104,

DOI

10.1002/Adma.201700104.


29


Page 30 of 32

21. Wang, W.; Zhou, J. H.; Wang, Z. P.; Zhao, L. Y.; Li, P. H.; Yang, Y.; Yang, C.; Huang, H. X.; Guo, S. J. Short-Range Order in Mesoporous Carbon Boosts Potassium-Ion Battery

Performance.

Adv.

Energy

Mater.

2018,

8

(5),

1701648,

DOI

10.1002/Aenm.201701648. 22. Xie, Y. H.; Chen, Y.; Liu, L.; Tao, P.; Fan, M. P.; Xu, N.; Shen, X. W.; Yan, C. L. UltraHigh Pyridinic N-Doped Porous Carbon Monolith Enabling High-Capacity K-Ion Battery Anodes for Both Half-Cell and Full-Cell Applications. Adv. Mater. 2017, 29 (35), 1702268, DOI 10.1002/Adma.201702268. 23. Jian, Z. L.; Xing, Z. Y.; Bommier, C.; Li, Z. F.; Ji, X. L. Hard Carbon Microspheres: Potassium-Ion Anode Versus Sodium-Ion Anode. Adv. Energy Mater. 2016, 6 (3), 1501874, DOI 10.1002/Aenm.201501874. 24. Share, K.; Cohn, A. P.; Carter, R. E.; Pint, C. L. Mechanism of potassium ion intercalation staging in few layered graphene from in situ Raman spectroscopy.

Nanoscale 2016, 8 (36), 16435-16439, DOI 10.1039/c6nr04084e. 25. Song, J. X.; Yu, Z. X.; Gordin, M. L.; Li, X. L.; Peng, H. S.; Wang, D. H. Advanced Sodium Ion Battery Anode Constructed via Chemical Bonding between Phosphorus,


30

Page 31 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Carbon Nanotube, and Cross-Linked Polymer Binder. ACS Nano 2015, 9 (12), 1193311941, DOI 10.1021/acsnano.5b04474. 26. Clark, D. T.; Fok, T.; Roberts, G. G.; Sykes, R. W. An investigation by electron spectroscopy for chemical analysis of chemical treatments of the (100) surface of n-type InP epitaxial layers for Langmuir film deposition. Thin Solid Films 1980, 70 (2), 261-283, DOI 10.1016/0040-6090(80)90367-3. 27. Chowdari, B. V. R.; Tan, K. L.; Chia, W. T.; Gopalakrishnan, R. X-Ray Photoelectron Spectroscopic Studies of Molybdenum Phosphate Glassy System. J. Non-Cryst. Solids 1990, 119 (1), 95-102, DOI Doi 10.1016/0022-3093(90)90245-H. 28. Yu, Z. X.; Song, J. X.; Wang, D. W.; Wang, D. H. Advanced anode for sodium-ion battery with promising long cycling stability achieved by tuning phosphorus-carbon nanostructures. Nano Energy 2017, 40, 550-558, DOI 10.1016/j.nanoen.2017.08.019.


31


Page 32 of 32

TOC Graphic:

Insights into high initial Coulombic efficiency and supieror cyclic performance for P/C composite anodes for potassium-ion batteries are revealed.


32

Carbon Composite Anode for Potassium-Ion Batteries

Recommend Documents