Toward Solid-State 3D-Microbatteries Using Functionalized

Subscriber access provided by University of Florida | Smathers Libraries

Article

Towards Solid-State 3D-Microbatteries using Functionalized Polycarbonate-based Polymer Electrolytes Bing Sun, Habtom Desta Asfaw, David Rehnlund, Jonas Mindemark, Leif Nyholm, Kristina Edstrom, and Daniel Brandell ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13788 • Publication Date (Web): 04 Dec 2017 Downloaded from http://pubs.acs.org on December 4, 2017

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 25 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 Applied Materials & Interfaces

Towards Solid-State 3D-Microbatteries using Functionalized Polycarbonate-based Polymer Electrolytes Bing Sun1,2, Habtom Desta Asfaw1,3, David Rehnlund1, Jonas Mindemark1, Leif Nyholm1, Kristina Edström1, Daniel Brandell1,* 1

Department of Chemistry – Ångström Laboratory, Uppsala University, Box 538, 75121 Uppsala, Sweden

2

Present address: Electrochemical Energy Storage Section, Electrochemistry Laboratory, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 3

Present address: Department of Chemistry, Faculty of Nature Sciences, Imperial College London, SW7 2AZ London, United Kingdom

*Corresponding author: [email protected]

KEYWORDS Li-battery, 3D-microbattery, polymer electrolyte, nanopillars, carbon foam

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 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 25

ABSTRACT

3D-microbatteries (3D-MBs) impose new demands for the selection, fabrication and compatibility of the different battery components. Herein, solid polymer electrolytes (SPEs) based on poly(trimethylene carbonate) (PTMC) have been implemented in 3D-MB systems. 3D electrodes of two different architectures, LiFePO4-coated carbon foams and Cu2O-coated Cu nanopillars, have been coated with SPEs and used in Li-cells. Functionalized PTMC with hydroxyl end groups was found to enable uniform and well-covering coatings on LiFePO4coated carbon foams, which was difficult to achieve for non-functionalized polymers, but the cell cycling performance was limited. By employing a SPE prepared from a copolymer of TMC and caprolactone (CL), with higher ionic conductivity, Li-cells composed of Cu2O-coated Cu nanopillars were constructed and tested both at ambient temperature and 60 °C. The footprint areal capacity of the cells was ca. 0.02 mAh cm-2 for an area gain factor (AF) of 2.5, and 0.2 mAh cm-2 for a relatively dense nanopillar-array (AF=25) at a current density of 0.008 mA cm-2 under ambient temperature (22±1 °C). These results provide new routes towards the realization of all-solid-state 3D-MBs.


2

Page 3 of 25 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 Three-dimensional microbatteries (3D-MBs) are energy storage devices intended for a large range of microelectronic applications including medical implants, autonomous sensors and telecommunication devices. 1 The limited volume available in these devices (1–10 mm3) requires the battery to be made with a minimum volume while still being able to provide adequate energy and power densities. These requirements impose enormous challenges regarding the electrode design, choice of active materials, integration of suitable electrolytes as well as the development of facile cell assembly steps for 3D-MBs.2 Although a large variety of 3D-electrodes in the micro- or nano-scale regime have been developed – including nanotubes, nanopillars and porous foams2–4 – a corresponding development of suitable electrolyte systems for 3D-MBs is still to be realized. All-solid-state 3D-MBs in this context constitute a desirable battery concept in terms of volume minimization (as thin electrolytes can be used) and battery safety (as there is no risk of electrolyte leakage).5,6 The limited advancement within the solid electrolyte field has, however, hindered the development of all-solid-state 3D-MBs. Liquid electrolytes are still used in most 3D-MB prototypes due to their high ionic conductivities, yielding good cell performances at room temperature.7–11 However, the safety and leakage concerns of these cells, as well as their relatively low volumetric energy densities, may significantly limit their practical use.12,13 In this context, solid polymer electrolytes (SPEs) offer advantages in terms of safety, mechanical integrity towards volume changes, chemical stability, versatility with respect to molecular modifications and ease of processing.13–17 SPEs have therefore been considered desirable electrolyte systems for all-solid-state 3D batteries,3–6,16 even though the major challenge to attain sufficiently high room-temperature ionic conductivities remains to be overcome. In comparison with ceramic solid electrolytes,16 SPEs facilitate the


3


Page 4 of 25

attainment of thin, flexible and adhesive coatings on microscopic surfaces. As this enables use as versatile separators together with Li-metal electrodes to yield less problems with lithium dendrite growth than with most liquid electrolytes,17 SPEs are very attractive for the development of 3DMBs. A few research groups have presented possible fabrication routes to integrate gel or hybrid polymer electrolytes into 3D-MBs, primarily by soaking a polymer matrix with conventional liquid electrolytes7,9–11,18,19 or by electrodepositing electronically insulating polymer layers directly on electrode surfaces.20–25 Recent advances using atomic layer deposition (ALD) techniques showed that controlled deposition of inorganic electrolytes,26 such as LiPON separating LiCoO2 and Si electrodes for 3D-MB applications, can be achieved.27 Alternatively, the integration of polyether-derived polymers on non-planar electrode surfaces has been demonstrated, for instance, the self-assembly of polyethylene amine-based oligomers21,28 and poly(propylene oxide)-derived oligomers electropolymerized on 3D Cu2O-nanopillars.23 Other recent examples also include initiated chemical vapor deposition polymerization (iCVD) of vaporized monomers on Si nanowires to produce nano-sized polymer coatings at ambient temperatures.29 The dependence on liquid electrolyte components to provide sufficient ion transport, or complex deposition conditions, however, leaves issues associated with their integration in practical cells unsolved. In this study, we focus on the integration of SPEs in 3D-MBs and for the first time evaluate their practical performance in these types of cells. We particularly exploit electrolytes based on poly(trimethylene carbonate) (PTMC) hosts, which provide good design flexibility as promising alternatives to conventional SPEs based on poly(ethylene oxide) (PEO).30–37 The conventional PEO-based SPEs commonly exhibit limited ion transport rates, e.g., room temperature (RT) ionic


4

Page 5 of 25 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


conductivities from 10-5 to 10-8 S cm-1 and cationic transference numbers t+ of ca. 0.2 to 0.3 for PEOxLiTFSI.38,39,40 In comparison, the present PTMC-based SPEs are modified either with functional side-groups that can provide different surface functionalities (i.e., hydroxyl groups)32 or increased flexibility by co-polymerization with ester units (i.e., caprolactone).33,34 High cation transference numbers (t+>0.6) and ionic conductivities of the order of 10-5 S cm-1 at room temperature, have previously been obtained for PTMC-based SPEs.33,34,41 Experimental and computational investigations on the origin of these favorable electrolyte properties point towards weaker ion binding in polycarbonates and polyesters compared to PEO and PEO-like segments.41-43 The use of PTMC-based SPEs in 3D-MBs which can operate at ambient temperatures constitutes an important step towards the realization of all-solid-state 3D-MBs. All these advantageous functionalities enable the use of thin SPE coatings directly integrated on 3D electrode surfaces which facilitates the design of all-solid 3D-MB prototypes. Two different 3D electrode substrates based on porous carbon foams (representing an aperiodic sponge architecture) and Cu nanopillars (representing an interdigitated architecture) are employed and the sequential deposition of the corresponding active materials – LiFePO4 on carbon foam and Cu2O on Cu nanopillars – is described and evaluated in SPE-based 3D-MB cells at ambient temperature (22±1 °C) and 60 °C.

EXPERIMENTAL METHODS

LiFePO4-coating of emulsion-templated carbon foams Emulsion-templated carbon foams were manufactured from high internal phase emulsion polymers (polyHIPE) using previously described procedures.44,45 Thin pieces of the carbon foams were immersed in a sol-gel LiFePO4 precursor, composed of 0.5 M FeSO4·7H2O (Sigma-


5


Page 6 of 25

Aldrich, ≥ 99.0%), 0.5 M NH4H2PO4 (Merck, 99.0 %), 0.5 M LiOOCCH3 (Merck), and 1 M citric acid (Merck, ≥ 99.5%) dissolved in a 9:1 mixture of distilled water and methanol (SigmaAldrich, ≥ 99.6%), for 48 hours. The gel-coated foams were then taken out of the solution and dried overnight at 70 °C in air and subsequently in vacuum at 120 °C to eliminate traces of water. The foams were then subjected to thermal pyrolysis at 700 °C in an argon atmosphere to yield a layer of LiFePO4 with a thickness of around 200 nm on the surfaces of the foams. Electrodeposition of 3D Cu2O-Cu nanopillars 3D Cu nanopillar current collectors were manufactured by template assisted electrodeposition in an aqueous solution containing CuSO4·5H2O (100 g L-1, Merck), (NH4)2SO4 (20 g L-1, Merck) and diethyltriamine (DETA, 80 mL L-1, Fluka) as previously described.46,47 An initial potential pulse to -1.5 V vs. Cu was followed by a pulsed current program consisting of cathodic pulses of 2 mA/cm2 for 0.25 s, 30 mA/cm2 for 0.05 s and 0 mA/cm2 for 0.5 s. The pulsed-current program was repeated 4000 times to obtain Cu nanopillars with an average length of 2 to 8 µm. The diameters of the nanopillars were controlled by template assisted electrodeposition using polycarbonate (PC) membranes (Cyclopore, Whatman) containing pores with a diameter of 1 or 2 µm. After the deposition, the PC template was dissolved in dichloromethane (Sigma Aldrich) to yield a 3D current collector with an inherent Cu2O surface oxide layer.46,47 Polymer electrolyte fabrication on 3D electrodes Two polycarbonate based host polymers were synthesized for use as SPEs: PTMC with 10% of the monomers functionalized by OH-groups (P(TMC-OH)) and a 20% TMC and 80% caprolactone (CL) random co-polymer (P(TMC-CL)). Detailed descriptions of the polymer synthesis and characterization procedures are provided elsewhere.32,33 The ionic conductivities and transport number data for these different PTMC-based SPEs have also been reported


6

Page 7 of 25 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


previously32,34,35 and a comparison of the ionic conductivities is provided in the Supporting Information (Fig. S1). Diluted homogenous mixtures with controlled mass loadings of highmolecular-weight polymers (457 000 g mol-1 for P(TMC-OH) and 246 000 to 338 000 g mol-1 for the copolymer32,34) doped with LiTFSI (Purolyte, dried at 120 °C for 48 h) in anhydrous acetonitrile (Sigma Aldrich) were prepared to form polymer coatings with a thickness of a few micrometers. A molar [TMC-OH]:[Li+] ratio of 8:1 and a [TMC20CL80]:[Li+] ratio of 4.6:1 were chosen based on previous results regarding their optimal ionic conductivities.32,34 The P(TMC-OH) system was coated on LiFePO4-carbon foams by dipping the electrode into the polymer solution for up to 6 hours. The obtained electrolyte thicknesses were estimated to be less than 5 µm using SEM. For comparison, the PTMC analogue without the OH functionalization was also subjected to the same treatments. For the Cu2O-nanopillar electrodes, diluted P(TMC-CL)-LiTFSI in acetonitrile was dipped onto the substrate and left to slowly infiltrate the volume between the nanopillars at RT in a glovebox overnight. The solvent was then removed by drying under vacuum (down to 1 mbar) at 60 °C for 20 hours. Surface analysis The morphology of the polymer coated electrodes was examined with a ZEISS Merlin highresolution scanning electron microscope (HR-SEM) equipped with an Aztec energy-dispersive X-ray spectroscopy (EDX) system. The accelerating voltage used for the EDX analysis on the SPE-coated samples was 10 to 12 kV. Electrochemical cycling The electrochemical performance of the electrodes was examined by galvanostatic cycling at different current densities between 0.05 and 3 V vs. Li+/Li at RT and 60 °C for the Cu nanopillar electrodes with the native Cu2O thin film serving as the active material. The cycling study on


7


Page 8 of 25

LiFePO4-carbon foam electrode coated with SPE was performed between 2.7 and 4.2 V vs. Li+/Li using a current density of 0.005 mA cm-2.

RESULTS AND DISCUSSION

Two fabrication routes were investigated to build all-solid-state Li-polymer 3D-MBs based on an aperiodic foam and a nanopillar electrode architecture, respectively. Schematic illustrations of the electrode fabrication and cell assembly are shown in Figure 1. The first scheme in Fig. 1a shows the sequential deposition of a porous layer of LiFePO4 onto a carbon foam substrate via a sol-gel approach and the formation of a micrometer thick layer of the SPE on the LiFePO4. In the second scheme (Fig. 1b), a 3D-microbattery was manufactured by infiltrating the SPE into the empty spaces between the Cu2O-coated Cu nanopillars; here, the Cu2O and the Cu nanopillars act as the active material and current collector, respectively. With both electrode designs Li foils were used as combined counter and reference electrodes. It is known that the fabrication of thin and completely covering solid electrolytes onto 3D electrodes is a challenging task,5,12,21,23,48,49 which becomes increasingly difficult with increasing geometrical complexity of the electrode. The surface area of the electrode is usually expressed using the area gain factor (AF) which is a geometrical figure-of-merit used to estimate the increase in the energy density per footprint surface area of a 3D-MB electrode.2,12 The AF is defined as the ratio between the total electrochemically active surface area and its footprint area for a given 3D electrode and the AF value for the carbon foam was previously reportedly to exceed 90.44 For the Cu2O/Cu nanopillar architecture, electrodes with estimated AFs of ca. 2.5 and 25 were prepared using PC membranes with different pore sizes (i.e., 2 and 1 µm).10 The use of the membrane with 1 µm pores resulted in less space between the nanopillars and thus a


8

Page 9 of 25 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


denser nanopillar arrangement, i.e., AF=25. The SEM images of the bare substrates seen in Fig. S2 were used to estimate the AFs.

Figure 1. Schematic illustrations showing the step-by-step fabrication of the all-solid-state Lipolymer 3D-microbatteries based on (a) a LiFePO4-coated carbon foam electrode and (b) a Cu2O-coated Cu nanopillar electrode. Previous studies have featured uniform nano-sized SPE coatings on 3D nanopillar electrodes obtained by electropolymerization of acrylic oligomers.6 The latter electropolymerization approach, however, proved to be less successful for the highly porous and complex LiFePO4coated carbon foam electrode architectures which feature an aperiodic arrangement of interconnected macro pores (see Fig. S2). The reason for this was that short-circuiting occurred during the cell assembly in all cases. The short-circuiting problem indicated above may pose a general problem when nanometer-scale thin SPE layers are employed for 3D-MBs since polymer materials possess both ionic and electronic conductivity. This means that the electronic


9


Page 10 of 25

conductivity of the SPE also needs to be taken into consideration as a too thin SPE layer can give rise to a significant leakage current between the electrodes. This can perhaps be illustrated using the following example. If we assume a potential difference of 3 V between the electrodes and an SPE thickness of 10 nm, an electric field strength in the SPE of 3×109 V m−1 would clearly be obtained. Moreover, if a maximum leakage current density of 0.02 µA cm−2 is allowed (which incidentally is a rather high current for a 3D-MB), the electronic resistivity of the SPE layer would have to be at least 1.5×1014 Ω cm (corresponding to an electronic conductivity of about 6.7×10−15 S cm−1). While this is well in the range of many well-known bulk polymers (resistivity values of 1015–1020 Ω cm are typical), it is far from obvious that the necessary resistance could be reliably obtained in nm-thin films of polymer electrolyte; hence, it is clear that the electronic conductance of ultrathin SPEs will constitute a challenge. The thickness of the SPE layer must consequently be increased sufficiently to minimize the leakage current between the electrodes. Another practical criterion that must not be overlooked while applying SPEs for high-surfacearea electrodes, especially those with aperiodic architecture, is complete and even surface coverage to provide sufficient electronic blocking. Due to these concerns, the experiments with the porous carbon foam electrodes were first carried out in favor of micro-sized SPE layers with surfactant properties. Solvent-free electrolytes based on PTMC, functionalized P(TMC-OH) and P(TMC-CL) doped with LiTFSI was compared during our first evaluation to integrate them in 3D foam electrodes. These SPEs had different functionalities depending on their side groups and backbone structures, which influenced both their transport properties and the physical properties of the electrode/SPE interface. When the conventional PTMC-based electrolyte was used (see Fig. 2a-b, Fig. S4a), clear heterogeneities were observed in the polymer coating. This is particularly visible in the


10

Page 11 of 25 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


shadowed regions for the foam substrate. Moreover, the EDX results in Fig. S3 and Fig. S4e clearly show substrate signals for the samples coated with the PTMC or PTMC-CL copolymer based SPEs, indicating that the coverage of these polymer coatings was incomplete. These cells also short-circuited immediately after the assembly, which could be a result of the incomplete SPE layer between the two electrodes. In contrast, significantly better results were obtained with the OH-functionalized PTMC which can be attributed to the favorable adsorption and strong adhesion through hydrogen bonding between the surface oxygen atoms and OH functional groups. Previous comparative studies using scratch-tests on P(TMC-OH) and PTMC-coated Cu2O and TiO2 flat substrates have demonstrated an improved adhesion strength for P(TMCOH) as compared to PTMC.31 Here, in the case of the porous substrates, the positive effect of introducing functional groups was also found for the LiFePO4 layer on the carbon foams. As seen in Fig. 2c-d and Fig. S4b, a much more even polymer coating was achieved compared to that for the original PTMC. The suppressed Fe and P signals from the LiFePO4 coating in the EDX maps (Fig. S3) indicate that a relatively complete and even coating of P(TMC-OH) on the order of a few µm was achieved on the substrate. As a result, the electrochemical cell could be fabricated without any short-circuiting. These results highlight the importance of using polymer functionalization to promote the surface attachment and the coverage of the sophisticated foam architectures.


11


Page 12 of 25

Figure 2. SEM images depicting the LiFePO4-carbon foam coated with (a-b) non-functionalized PTMC8LiTFSI, (c-d) functionalized PTMC–OH8LiTFSI, and (e-f) Cu2O-Cu nanopillars coated with PTMC-OH8LiTFSI. The complexity of the porous geometry of the carbon foams clearly increases the risk of shortcircuiting the SPE-based cells. Short-circuiting was observed for several other cells containing PTMC-based SPEs as well as cross-linked PPO-based SPEs derived from our previous study.23,45 Nonetheless, the Li-polymer 3DMB cell containing P(TMC-OH) coated foam was found to be the only system which did not fail in this sense. The voltage profile for the galvanostatic cycling of 3D LiFePO4-carbon foam cells is shown in Fig. S5. It can be seen that an open circuit voltage of around 3.2 V vs. Li+/Li was obtained at 60 °C. This potential value is somewhat lower than the 3.4 V obtained when using liquid electrolytes.51 Considering that the LiFePO4-coated carbon


12

Page 13 of 25 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


foam electrode is a binder-free system without additional electronic conducting additives, the polymer coating can serve as a combined electrolyte, separator and binder. It might therefore block the electronic conduction between the LiFePO4 particles while at the same time offering good surface attachments to particle surfaces. The limited interfacial contacts between the SPE layer and the Li surface might additionally affect the electrochemical cell performance. Overall, the practical cell performance observed for the LiFePO4-carbon foam cell can be considered unsatisfactory due to a possible combination of limitations in the bulk ionic conductivity, interfacial contacts with the counter electrode and the lack of electronic wiring, although the surfactant property obviously resulted in an improvement of coverage and uniformity – and device performance – of the SPE coatings as compared to those without surfactant groups. When the OH-functionalized SPE was coated on Cu2O-Cu nanopillars with a length of 2 to 8 µm (as illustrated in Fig. 2e and 2f), a relatively complete polymer coating was obtained. The length of the nanopillars made it more challenging to produce uniform coatings along the nanopillar surfaces as compared to the foam geometry. This problem can, however, be solved by using polymer coatings locally formed through in-situ techniques (e.g., pulsed-current electropolymerization and iCVD23,52) or simply employing infiltrated polymer electrolytes with enhanced ionic conductivities and Li+ transport properties. The latter cell construction using direct P(TMC-CL) SPE infiltration into the voids between the Cu2O coated Cu nanopillars (Fig 1b) constitutes a more straightforward 3DMB fabrication technique than that used for the carbon foam electrode. The polymer electrolyte solution can be expected to infiltrate the space between the nanopillars. Since cutting the 3D Cu substrate without damaging the coated SPE layer proved technically difficult, thereby preventing visualization of the cross-sections, the correlation between the areal capacity and the area gain factor of the electrode can provide information


13


Page 14 of 25

regarding the success of the SPE coverage process. When varying the distance between the nanopillars, the electrochemical areal capacity should vary accordingly if the SPE coating involves the inter-pillar spaces. As shown in Fig. 3, the footprint area capacity of the denser electrodes (AF=25) was found to be around 10 times higher than that for the electrode with the less dense structure (AF=2.5), indicating that the electrochemical areal capacities were almost equivalent. This suggests an effective wetting of the electrode surfaces by the polymer coating even for the denser nanopillar arrangement. A footprint area capacity of around 0.2 mAh cm-2 was achieved at a current density of 0.008 mA cm-2 (per footprint area). When taking the AF values into account, comparable areal capacities per electrochemical surface area were obtained for both cells: i.e. around 0.008 mAh cm-2 (as seen on the right y-axis in Fig. 3a and 3b) at a current density of 0.008 mA cm-2, suggesting that the capacity gain was indeed proportional to the surface area gain factor (i.e., AF) for these cells. This confirms that the influence from void spaces in the coated Cu2O electrodes was negligible and that the polymer electrolyte coatings were sufficiently uniform throughout the 3D electrode assembly to access to full areal capacity regardless of the density of the nanopillar arrangement. In Fig. 3c and 3d, it is seen that a capacity enhancement could be obtained by cycling at 60 °C where the ionic conductivity is significantly increased (as shown in Fig. S1). This facilitates faster ion conduction than that at RT and also improves the interfacial contacts as the polymer layer softens at higher temperatures. The relatively slow ion transport in the electrolyte at RT could explain the relatively low 1st cycle capacity in Fig. 3a. As seen in Fig. 3c, there was a distinct enhancement of the 1st cycle capacity which could be explained by the enhanced mass transport rate in the electrode and the improved Li-ion transport in the electrolyte. The mass transport rate within the electroactive layer of the Cu2O electrode thus also increases with


14

Page 15 of 25 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


increasing temperature. The footprint area capacity at 60 °C was found to be around 1.5 times larger than the RT value for the less dense substrate (AF=2.5) at a current density of 0.008 mA cm-2. Our previous XPS studies of the interfaces of SPE-based cells, in which the surface species of the electrode/SPE interfaces where studied after cycling at elevated temperatures (e.g., 50 °C),36,53 indicate that there was some degradation of the salt and the polymer matrix at the anode surfaces. In the present case, the capacities for each current density did not show any obvious fading at 60 °C, which suggests that the build-up of surface species did not have any detrimental effect during cycling up to one month. The cycling profile in Fig. 3d confirms that the voltage plateaus observed at 1.4 to 1.0 V and at potentials higher than 2.5 V vs. Li+/Li during the 1st discharge/charge were consistent with the reduction of Cu2O and the oxidation of Cu, respectively.46,54 In liquid electrolyte based cells, pulverization of Cu2O due to electrochemical milling can lead to an increase in the active surfaces of the particles, which can contribute to an enhancement in capacity during successive cycling.46 When using the present solid electrolytes such an effect was, however, not observed. This is likely due to the fact that the freshly created electrode surfaces, as a result of electrochemical milling, are not accessible by the less diffusive SPE, at least at ambient temperatures. Stable cycling could hence be achieved at 60 °C and ambient temperature (i.e., 22±1 °C). The latter is notable considering traditional PEO-based SPEs cannot be cycled at RT, in contrast to the important advances of polycarbonate-based SPEs which operate well from high to ambient temperatures.34,55


15


Page 16 of 25

Figure 3. Cycling performance of two Li/P(TMC-CL)-LiTFSI/Cu2O/Cu-nanopillar cells with area gain factors of (a) 2.5 and (b) 25, respectively, at different cycling rates and temperatures (ab) 22±1 °C and (c) 60 °C; (d) the cycling voltage profiles of the cells. The solid symbols in a-c refer to the discharge capacities while the open ones represent the charge capacities. The footprint areal capacities (left-y axis) were calculated by normalizing the total capacity with respect to the substrate area, while the estimated areal capacities (right-y axis) were calculated based on the estimated electrochemically active surface area. The current density was calculated using the footprint area.


16

Page 17 of 25 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


CONCLUSIONS This work describes the application of solvent-free polymer electrolytes to two types of 3D electrodes based on a porous carbon foam and an array of copper nanopillars, respectively. The employed SPEs were derived from functional polycarbonates which have major advantages, either by surfactant properties or via enhanced ionic conductivity, as compared to conventional PEO-based SPEs. The functionalized P(TMC-OH) polymer electrolyte provided good coverage of the SPE coatings on the highly porous LiFePO4 carbon foam electrode. For the cells consisting of PTMC-based SPEs without such surfactant functionalization, short-circuits were observed, which might be resulting from incomplete coverage and/or poor attachments of the SPE. The cell cycling performance of LiFePO4 carbon foam coated by P(TMC-OH) was, however, still unsatisfactory. Furthermore, the copolymer P(TMC-CL) based SPEs with relatively high ionic conductivity showed promising electrochemical performance both at room temperature and at 60 °C when using a 3D electrode based on Cu2O-coated Cu nanopillars infiltrated with the copolymer SPE. Stable cycling with capacities of ca. 0.2 mAh cm-2 footprint area at AF=25 could be achieved at ambient temperature 22±1 °C. An alternative and effective approach in electrolyte development has thus been demonstrated in conjunction with state-ofthe-art 3D electrode designs. ACKNOWLEDGEMENT This work has been supported by STandUP for Energy. Dr. Mario Valvo (Uppsala University) and Dr. Matthew Roberts (University of Oxford) are acknowledged for fruitful discussions. CONFLICTS OF INTEREST The authors declare no competing financial interest.


17


Page 18 of 25

ASSOCIATED CONTENT Supporting Information. The Supporting Information contains supplementary results of the ionic conductivities of the different PTMC-based SPEs, SEM images of the bare 3D electrodes, EDX results of SPE-coated LiFePO4 carbon foam electrodes as well as the first electrochemical cycling of the SPE-coated LiFePO4 carbon foam Li-cell. REFERENCES (1)

Ferrari, S.; Loveridge, M.; Beattie, S. D.; Jahn, M.; Dashwood, R. J.; Bhagat, R. Latest

Advances in the Manufacturing of 3D Rechargeable Lithium Microbatteries. J. Power Sources 2015, 286, 25–46. (2)

Roberts, M.; Johns, P.; Owen, J.; Brandell, D.; Edström, K.; Enany, G. El; Guery, C.;

Golodnitsky, D.; Lacey, M.; Lecoeur, C.; Mazor, H.; Peled, E.; Perre, E.; Shaijumon, M. M.; Simon, P.; Taberna, P.-L. 3D Lithium Ion Batteries—from Fundamentals to Fabrication. J. Mater. Chem. 2011, 21 (27), 9876–9890. (3)

Edström, K.; Brandell, D.; Gustafsson, T.; Nyholm, L. Electrodeposition as a Tool for 3D

Microbattery Fabrication. Electrochem. Soc. Interface 2011, 20 (2), 41–46. (4)

Long, J. W.; Dunn, B.; Rolison, D. R.; White, H. S. Three-Dimensional Battery

Architectures. Chem. Rev. 2004, 104 (10), 4463–4492. (5)

Arthur, T. S.; Bates, D. J.; Cirigliano, N.; Johnson, D. C.; Malati, P.; Mosby, J. M.; Perre,

E.; Rawls, M. T.; Prieto, A. L.; Dunn, B. Three-Dimensional Electrodes and Battery Architectures. MRS Bull. 2011, 36 (7), 523–531.


18

Page 19 of 25 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


(6)

Mario, V.; Roberts, M.; Oltean, G.; Sun, B.; Rehnlund, D.; Brandell, D.; Nyholm, L.;

Gustafsson, T.; Edström, K. Electrochemical Elaboration of Electrodes and Electrolytes for 3D Structured Batteries. J. Mater. Chem. A 2013, 1 (32), 9281–9293. (7)

Dokko, K.; Sugaya, J.; Nakano, H.; Yasukawa, T.; Matsue, T.; Kanamura, K. Sol–gel

Fabrication of Lithium-Ion Microarray Battery. Electrochem. Commun. 2007, 9 (5), 857–862. (8)

Pikul, J. H.; Gang Zhang, H.; Cho, J.; Braun, P. V; King, W. P. High-Power Lithium Ion

Microbatteries from Interdigitated Three-Dimensional Bicontinuous Nanoporous Electrodes. Nat. Commun. 2013, 4 (1732), 1–5. (9)

Sun, K.; Wei, T. S.; Ahn, B. Y.; Seo, J. Y.; Dillon, S. J.; Lewis, J. A. 3D Printing of

Interdigitated Li-Ion Microbattery Architectures. Adv. Mater. 2013, 25, 4539–4543. (10)

Ergang, N. S.; Fierke, M. A.; Wang, Z.; Smyrl, W. H.; Stein, A. Fabrication of a Fully

Infiltrated Three-Dimensional Solid-State Interpenetrating Electrochemical Cell. J. Electrochem. Soc. 2007, 154 (12), A1135–A1139. (11)

Min, H.-S.; Park, B. Y.; Taherabadi, L.; Wang, C.; Yeh, Y.; Zaouk, R.; Madou, M. J.;

Dunn, B. Fabrication and Properties of a Carbon/polypyrrole Three-Dimensional Microbattery. J. Power Sources 2008, 178 (2), 795–800. (12)

Oudenhoven, J. F. M.; Baggetto, L.; Notten, P. H. L. All-Solid-State Lithium-Ion

Microbatteries: A Review of Various Three-Dimensional Concepts. Adv. Energy Mater. 2011, 1 (1), 10–33. (13)

Roth, E. P.; Orendorff, C. J. How Electrolytes Influence Battery Safety. Electrochem.

Soc. Interface 2012, 21 (2), 45–49. (14)

Armand, M.; Tarascon, J.-M. Building Better Batteries. Nature 2008, 451 (7179), 652–

657.


19


(15)

Page 20 of 25

Hallinan, D. T.; Balsara, N. P. Polymer Electrolytes. Annu. Rev. Mater. Res. 2013, 43 (1),

503–525. (16)

Quartarone, E.; Mustarelli, P. Electrolytes for Solid-State Lithium Rechargeable

Batteries: Recent Advances and Perspectives. Chem. Soc. Rev. 2011, 40 (5), 2525–2540. (17)

Takeda, Y.; Yamamoto, O.; Imanishi, N. Lithium Dendrite Formation on a Lithium Metal

Anode from Liquid, Polymer and Solid Electrolytes. Electrochemistry 2016, 84 (4), 210–218. (18)

Nathan, M.; Golodnitsky, D.; Yufit, V.; Strauss, E.; Ripenbein, T.; Shechtman, I.;

Menkin, S.; Peled, E. Three-Dimensional Thin-Film Li-Ion Microbatteries for Autonomous MEMS. J. Microelectromechanical Syst. 2005, 14 (5), 879–885. (19)

Golodnitsky, D.; Nathan, M.; Yufit, V.; Strauss, E.; Freedman, K.; Burstein, L.;

Gladkich, A.; Peled, E. Progress in Three-Dimensional (3D) Li-Ion Microbatteries. Solid State Ionics 2006, 177 (26–32), 2811–2819. (20)

Rhodes, C. P.; Long, J. W.; Doescher, M. S.; Fontanella, J. J.; Rolison, D. R. Nanoscale

Polymer Electrolytes: Ultrathin Electrodeposited Poly(phenylene Oxide) with Solid-State Ionic Conductivity. J. Phys. Chem. B 2004, 108 (35), 13079–13087. (21)

Sun, B.; Liao, I.-Y.; Tan, S.; Bowden, T.; Brandell, D. Solid Polymer Electrolyte Coating

from a Bifunctional Monomer for Three-Dimensional Microbattery Applications. J. Power Sources 2013, 238, 435–441. (22)

El-Enany, G.; Lacey, M. J.; Johns, P. A.; Owen, J. R. In Situ Growth of Polymer

Electrolytes on Lithium Ion Electrode Surfaces. Electrochem. Commun. 2009, 11 (12), 2320– 2323.


20

Page 21 of 25 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


(23)

Sun, B.; Rehnlund, D.; Lacey, M. J.; Brandell, D. Electrodeposition of Thin

Poly(propylene Glycol) Acrylate Electrolytes on 3D-Nanopillar Electrodes. Electrochim. Acta 2014, 137, 320–327. (24)

Kyeremateng, N. A.; Dumur, F.; Knauth, P.; Pecquenard, B.; Djenizian, T.

Electrodeposited Copolymer Electrolyte into Nanostructured Titania Electrodes for 3D Li-Ion Microbatteries. Comptes Rendus Chim. 2013, 16 (1), 80–88. (25)

Chen, N.; Reeja-jayan, B.; Lau, J.; Moni, P.; Liu, A.; Gleason, K. K. Nanoscale,

Conformal Polysiloxane Thin Film Electrolytes for Three-Dimensional Battery Architectures. Mater. Horizons 2015, 2, 309–314. (26)

Kozen, A. C.; Pearse, A. J.; Lin, C.-F.; Noked, M.; Rubloff, G. W. Atomic Layer

Deposition of the Solid Electrolyte LiPON. Chem. Mater. 2015, 27 (15), 5324–5331. (27)

Talin, A. A.; Ruzmetov, D.; Kolmakov, A.; McKelvey, K.; Ware, N.; El Gabaly, F.;

Dunn, B.; White, H. S. Fabrication, Testing, and Simulation of All-Solid-State ThreeDimensional Li-Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8 (47), 32385–32391. (28)

Tan, S.; Perre E.; Gustafsson, T.; Brandell, D. A Solid State 3-D Microbattery based on

Cu2Sb Nanopillar Anodes. Solid State Ionics. 2012, 225, 510-512. (29)

Xu, J.; Gleason, K. K. Conformal Polymeric Thin Films by Low-Temperature Rapid

Initiated Chemical Vapor Deposition (iCVD) Using Tert-Butyl Peroxybenzoate as an Initiator. ACS Appl. Mater. Interfaces 2011, 3 (7), 2410–2416. (30) Mindemark, J.; Bowden, T. Synthesis and Polymerization of Alkyl Halide-Functional Cyclic Carbonates. Polymer 2011, 52 (25), 5716–5722. (31)

Mindemark, J.; Bowden, T. Diversity in Cyclic Carbonates: Synthesis of Triazole-

Functional Monomers Using Click Chemistry. Polym. Chem. 2012, 3, 1399–1401.


21


(32)

Page 22 of 25

Mindemark, J.; Sun, B.; Brandell, D. Hydroxyl-Functionalized Poly(trimethylene

Carbonate) Electrolytes for 3D-Electrode Configurations. Polym. Chem. 2015, 6 (26), 4766– 4774. (33)

Mindemark, J.; Törmä, E.; Sun, B.; Brandell, D. Copolymers of Trimethylene Carbonate

and ε-Caprolactone as Electrolytes for Lithium-Ion Batteries. Polymer 2015, 63, 91–98. (34)

Mindemark, J.; Sun, B.; Törmä, E.; Brandell, D. High-Performance Solid Polymer

Electrolytes for Lithium Batteries Operated at Ambient Temperature. J. Power Sources 2015, 298, 166–170. (35)

Sun, B.; Mindemark, J.; Edström, K.; Brandell, D. Polycarbonate-Based Solid Polymer

Electrolytes for Li-Ion Batteries. Solid State Ionics 2014, 262, 738–742. (36)

Sun, B.; Xu, C.; Mindemark, J.; Gustafsson, T.; Edström, K.; Brandell, D. At the Polymer

Electrolyte Interfaces: The Role of the Polymer Host in Interphase Layer Formation in LiBatteries. J. Mater. Chem. A 2015, 3 (26), 13994–14000. (37)

Sun, B.; Mindemark, J.; Edström, K.; Brandell, D. Realization of High Performance

Polycarbonate-Based Li Polymer Batteries. Electrochem. Commun. 2015, 52, 71–74. (38)

Fergus, J. W. Ceramic and Polymeric Solid Electrolytes for Lithium-Ion Batteries. J.

Power Sources 2010, 195 (15), 4554–4569. (39)

Borodin, O.; Smith, G. D. Mechanism of Ion Transport in Amorphous Poly(ethylene

oxide)/LiTFSI from Molecular Dynamics Simulations. Macromolecules 2006, 39 (4), 1620– 1629. (40)

Gorecki, W.; Jeannin, M.; Belorizky, E.; Roux, C.; Armand, M. Physical Properties of

Solid Polymer Electrolyte PEO(LiTFSI) Complexes. J. Phys. Condens. Matter 1995, 7, 6823– 6832.


22

Page 23 of 25 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


(41)

Sun, B.; Mindemark, J.; V. Morozov, E.; Costa, L. T.; Bergman, M.; Johansson, P.; Fang,

Y.; Furó, I.; Brandell, D. Ion Transport in Polycarbonate Based Solid Polymer Electrolytes: Experimental and Computational Investigations. Phys. Chem. Chem. Phys. 2016, 18, 9504–9513. (42)

Nakamura, M.; Tominaga, Y. Utilization of Carbon Dioxide for Polymer Electrolytes

[II]: Synthesis of Alternating Copolymers with Glycidyl Ethers as Novel Ion-Conductive Polymers. Electrochim. Acta 2011, 57 (1), 36–39. (43)

Morioka, T.; Ota, K.; Tominaga, Y. Effect of Oxyethylene Side Chains on Ion-

Conductive Properties of Polycarbonate-Based Electrolytes. Polymer 2016, 84, 21–26. (44) Asfaw, H. D.; Roberts, M. R.; Tai, C.-W.; Younesi, R.; Valvo, M.; Nyholm, L.; Edström, K. Nanosized LiFePO4-Decorated Emulsion-Templated Carbon Foam for 3D Micro Batteries: A Study of Structure and Electrochemical Performance. Nanoscale 2014, 6 (15), 8804–8813. (45)

Asfaw, H. D.; Roberts, M. R.; Younesi, R.; Edström, K. Emulsion-Templated

Bicontinuous Carbon Network Electrodes for Use in 3D Microstructured Batteries. J. Mater. Chem. A 2013, 1 (44), 13750–13758. (46)

Valvo, M.; Rehnlund, D.; Lafont, U.; Hahlin, M.; Edström, K.; Nyholm, L. The Impact of

Size Effects on the Electrochemical Behaviour of Cu2O-Coated Cu Nanopillars for Advanced Li-Ion Microbatteries. J. Mater. Chem. A 2014, 2, 9574–9586. (47)

Rehnlund, D.; Valvo, M.; Tai, C.-W.; Ångström, J.; Sahlberg, M.; Edström, K.; Nyholm,

L. Electrochemical Fabrication and Characterization of Cu/Cu2O Multi-Layered Micro and Nanorods in Li-Ion Batteries. Nanoscale 2015, 7 (32), 13591–13604. (48)

Dunn, B.; Long, J.; Ronson, D. Rethinking Multifunction in Three Dimensions for

Miniaturizing Electrical Energy Storage. Electrochem. Soc. Interface 2008, 17 (3), 49–53.


23


(49)

Page 24 of 25

Rhodes, C. P.; Long, J. W.; Pettigrew, K. A.; Stroud, R. M.; Rolison, D. R. Architectural

Integration of the Components Necessary for Electrical Energy Storage on the Nanoscale and in 3D. Nanoscale 2011, 3 (4), 1731–1740. (50)

Tan, S.; Walus, S.; Hilborn, J.; Gustafsson, T.; Brandell, D. Poly(ether Amine) and

Cross-Linked Poly(propylene Oxide) Diacrylate Thin-Film Polymer Electrolyte for 3DMicrobatteries. Electrochem. Commun. 2010, 12 (11), 1498–1500. (51)

Padhi, A. K.; Nnjundaswamy, K.S. Goodenough, J. B. Phospho-Olivines as Positive-

Electrode Materials for Rechargeable Lithium Batteries. J. Electrochem. Soc. 1997, 144 (4), 1–7. (52)

Chen, N.; Reeja-Jayan, B.; Liu, A.; Lau, J.; Dunn, B.; Gleason, K. K. iCVD Cyclic

Polysiloxane and Polysilazane as Nanoscale Thin-Film Electrolyte: Synthesis and Properties. Macromol. Rapid Commun. 2016, 37 (5), 446–452. (53)

Xu, C.; Sun, B.; Gustafsson, T.; Edström, K.; Brandell, D.; Hahlin, M. Interface Layer

Formation in Solid Polymer Electrolyte Lithium Batteries: An XPS Study. J. Mater. Chem. A 2014, 2 (20), 7256–7264. (54)

Lee, Y. H.; Leu, I. C.; Liao, C. L.; Chang, S. T.; Wu, M. T.; Yen, J. H.; Fung, K. Z.

Fabrication and Characterization of Cu2O Nanorod Arrays and Their Electrochemical Performance in Li-Ion Batteries. Electrochem. Solid-State Lett. 2006, 9 (4), A207–A210. (55)

Kimura, K.; Yajima, M.; Tominaga, Y. A Highly-Concentrated Poly(ethylene

Carbonate)-Based Electrolyte for All-Solid-State Li Battery Working at Room Temperature. Electrochem. commun. 2016, 66, 46–48.


24

Page 25 of 25 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


FOR TABLE OF CONTENTS ONLY


25

Toward Solid-State 3D-Microbatteries Using Functionalized

Recommend Documents