Crystal Orientation Dependence of Precipitate Structure of

Subscriber access provided by HACETTEPE UNIVERSITESI KUTUPHANESI

Article

Crystal orientation dependence of precipitate structure of electrodeposited Li metal on Cu current collectors Kohei Ishikawa, Yasumasa Ito, Shunta Harada, Miho Tagawa, and Toru Ujihara Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01710 • Publication Date (Web): 17 Apr 2017 Downloaded from http://pubs.acs.org on April 23, 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.

Crystal Growth & Design 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

Crystal Growth & Design

Crystal orientation dependence of precipitate structure of electrodeposited Li metal on Cu current collectors *Kohei Ishikawa†, Yasumasa Ito ‡, Shunta Harada †§, Miho Tagawa†§, Toru Ujihara†§ † Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. ‡ Department of Mechanical Science and Engineering, Nagoya University, Furo-cho, Chikusaku, Nagoya 464-8603, Japan. § Institute of Materials and Systems for Sustainability (IMaSS), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

ABSTRACT: Dendritic growth at the Li anode during charging is caused by a morphological inhomogeneity of Li electrodeposition. In this study, we investigate the dependence of the morphology of Li electrodeposited on a polycrystalline Cu current collector on the Cu grain orientation both experimentally and by numerical analysis. The experimental results show that the Li precipitates that form on Cu grains that have close to (111) orientations are the smallest and the most uniform in size. Such a morphology is expected to be effective for the suppression of dendrite growth. Numerical analysis indicates that the initial stage of electrodeposition plays

ACS Paragon Plus Environment

1


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

an important role in determining morphological variation, and this is due to the crystal orientation dependence of the adatom concentration at equilibrium.

Introduction Li metal is the most attractive anode material for rechargeable batteries because it has a low density and the most negative electrochemical potential among metals.1 The theoretical capacity of Li metal anodes (3860 mAh/g) is much higher than that of carbon-based anodes (339 mAh/g), which are commonly used for commercial batteries.2 However, short-circuiting due to non-uniform deposition (dendrites) while charging has prevented the commercialization of Li metal anodes due to short cycle life and associated safety issues.3 Several mechanisms have been proposed based on the diffusion of metal ions to elucidate the dendritic growth of electrodeposited metal. Barton and Bockris measured the growth rate of Ag dendrites and their tip radii,4 and the growth rate for a dendrite was determined to be faster than that for a flat surface because spherical diffusion conditions are dominant at the dendrite tip. Monroe and Newman applied this interpretation to Li electrodeposition and concluded that dendritic growth becomes accelerated with time,5 although it can be slowed down by a decrease in the current density at the dendrite tips and by an increase in the diffusivity of the metal ions. These models assume the presence of an initial protrusion on the electrode. A number of studies determined that the non-uniformity is caused by a solid electrolyte interphase (SEI) layer on the electrode surface. The SEI is formed by the chemical reaction of Li with the electrolyte. The SEI is intrinsically inhomogeneous due to a wide variety of possible surface reactions,6 which causes localized Li deposition at regions of the SEI that have higher ionic conductivity, and this becomes the origin of dendritic growth.7


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


The morphology of electrodeposited metal is known to be highly dependent on the crystal orientation of the substrate. This is true, for example, of Zn, Ni, Pb, and Cd on Cu substrates.8 Such morphological variations are attributed to the orientation dependence of charge transfer and the surface diffusion kinetics of the depositing metal. Mitsuhashi et al. have also reported that the crystal orientation of the substrate affects the morphology of deposited Zn,9 and a substrate with the (0001) orientation is likely to initiate non-uniform deposition due to the low diffusivity of the adatoms on the wide terrace structure of the (0001) surface. In an analogous way, the morphology of Li precipitates would also be expected to be affected by the crystal orientation of the current collector, especially in the initial stage of electrodeposition. However, few studies have approached the dendrite problem from this perspective. In the present study, experiments were conducted with an emphasis on the effect of the current collector crystal orientation on the Li morphology during electrodeposition. Moreover, a numerical analysis of Li nucleation and growth under galvanostatic conditions was conducted to elucidate the mechanism for the morphological variation of Li precipitates.

Materials and Methods Figure 1 shows the three-pole cell used for the galvanostatic charge experiments and a magnified image of the three electrodes.


3


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 4 of 25

Figure 1. (a) Three-pole cell used for the galvanostatic charge experiments and (b) magnified image of the three electrodes. The working electrode (WE) is polycrystalline Cu wire with a 0.5 mm diameter (Japan Metal Service, 99.9% purity). Prior to the experiments, the cross-sectional surface of the WE was polished with colloidal silica (COMPOL 80, Fujimi Inc.) for 30 min after grinding with #400 diamond abrasive papers (Maruto) and alumina polishing slurries (POLIPLA 608S, Fujimi Inc.).


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


Crystal orientation mapping was conducted for the polished Cu wire using electron backscatter diffraction (EBSD; PHI, 700Xi). The acceleration voltage and probe current for the primary electrons were 15.0 kV and 10 nA, respectively. The step width for scanning was 800 nm. Ar ion beam sputtering was conducted to clean the surface of the Cu current collectors before the EBSD analysis. The EBSD patterns were analyzed using an orientation imaging microscopy system (OIMTM, EDAX). Figure 2 shows a scanning electron microscopy (SEM) image of a Cu current collector and its crystal orientation map.


5


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 6 of 25

Figure 2. (a) SEM image of a Cu current collector and (b) crystal orientation map obtained by EBSD analysis. The Cu current collector was confirmed to be polycrystalline with no preferred crystal orientation. The counter electrode (CE) and the reference electrode (RE) were 1.0 mm diameter Li metal wires (Honjo Metal, 99.8% purity). The cell was filled with a commercial electrolyte


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


(Purelyte, UBE Industries) that consisted of 1 M LiPF6 in a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) with a 3:7 weight ratio. Galvanostatic experiments were conducted using an electrochemical measurement system (Hokuto Denko, HZ-7000). Li was electrodeposited at a current density of 5.0 mA/cm2 and charge capacities of 0.1 and 1.0 mAh/cm2. Both cell assembly and disassembly procedures were performed in an argon-purged glove box. The disassembled WE was rinsed with dimethyl carbonate (DMC; Sigma-Aldrich) to remove residual electrolyte. The precipitate structure of deposited Li was analyzed using SEM (Hitachi High-Technologies, S-4800). Matching with crystal orientation maps was conducted by comparing the characteristic contrast of low-magnification SEM images of Li precipitates. Elemental analysis of Li precipitates produced with a charge capacity of 1.0 mAh/cm2 was conducted using auger electron spectroscopy (AES) with a primary beam voltage of 10 kV. The auger spectrum was obtained after Ar ion sputtering at 3.0 kV for 10 min.

Results Figure 3 shows an SEM image of Li electrodeposited at a charge capacity of 0.1 mAh/cm2 and a crystal orientation map of the Cu current collector.


7


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 8 of 25

Figure 3. (a) SEM image of Li precipitated at a charge capacity of 0.1 mAh/cm2 and (b) crystal orientation map for the corresponding area of the Cu current collector. The SEM image of Li precipitates matches well with the distribution of crystal orientations on the current collector. The Li precipitates that were deposited on Cu grains with orientations close to (111) appear dark in the SEM image. Figure 4 shows magnified SEM images of Li precipitates at areas (i) and (ii) in Figure 3.


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


Figure 4. SEM images of Li precipitates with various size distributions on (a) area (i) and (b) area (ii) in Figure 3. Note that the Cu grains in area (i) have mainly high-index orientations, whereas in area (ii) they have mainly (111) orientations. Although most of the Li precipitates have the same spherical shape, there are clear differences in their size, size distribution, and number density. More specifically, Li precipitates form on Cu grains with orientations close to (111) are relatively small, uniform in size and are densely aggregated. To quantitatively and statistically evaluate the effects of the current collector crystal orientation on the Li morphology, the mean precipitate diameter, standard deviation of the


9


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 10 of 25

diameters, and the number density of precipitates were measured by image analysis at 100 randomly selected points in Figure 3. Figure 5 shows the distribution of the mean diameter ̅ , the standard deviation of the diameter , and the number density , of precipitate nuclei plotted on inverse pole figures for the Cu current collector. Figures 5(a) and 5(b) show that the precipitate size is small and the standard deviation is the lowest near the crystal zone axis, which is indicated as a yellow band, and near the Cu (001) orientation. The precipitates are particularly small and uniform in size near the Cu (111) orientation.


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


Figure 5. (a) Mean precipitate diameter, (b) standard deviation of the diameter, and (c) number density of Li nuclei plotted on inverse pole figures. The yellow band indicates the crystal zone axis. Figure 5(c) illustrates the effect of the crystal orientation on the number density of precipitates. The number density of Li nuclei is highest for orientations close to (111), where precipitates on grains with high-index orientations are sparsely aggregated. Therefore, the most uniformly sized


11


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 12 of 25

and compact precipitates are obtained for the (111) orientation, followed by the zone axis, and then the (001) orientation. The dependence of the morphology on the charge capacity was next investigated.

Figure 6. (a) SEM image of Li precipitated at a charge capacity of 1.0 mAh/cm2, and (b) crystal orientation map for the corresponding area of the Cu collector.


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


Figure 7. (a) Auger survey spectrum for Li precipitated at a charge capacity of 1.0 mAh/cm2, and (b) AES map for Li in the area indicated by the rectangular box in Figure 6(a). Figures 6(a) and 6(b) show SEM images at a charge capacity of 1.0 mAh/cm2. AES was applied at the area indicated in Fig. 6(a) to confirm the presence of Li on the Cu current collector. Figure 7(a) shows the AES spectrum obtained and Figure 7(b) shows an AES map for Li for the area indicated by the rectangular box in Figure 6(a). Figure 7 confirms that the Cu surface is completely covered by electrodeposited Li. However, Figure 6 indicate a variation in the contrast of Li precipitates due to the effect of crystal orientation for deposition at a charge capacity of 1.0 mAh/cm2. Figure 8 shows high magnification SEM images of Li precipitates at areas (i) and (ii) indicated in Figure 6(a).


13


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 14 of 25

Figure 8. SEM images of Li precipitates in (a) area (i) and (b) area (ii) in Fig. 6. The Li precipitates remained spherical at a charge capacity of 1.0 mAh/cm2. As seen in Figure 8(b), those on Cu grains with orientations close to (111) are more uniform in size than those on grains with high-index orientations (Figure 8(a)), which suggests that the crystal orientation of the current collector influences the surface morphology of Li for relatively long time charging.

Discussion The experimental results clearly indicate that the morphology of Li precipitates is affected by the crystal orientation of the Cu current collector. In addition, the initial process of Li


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


electrodeposition plays an important role in the variation of the morphology. Therefore, a numerical analysis was conducted to explicate the crystal orientation dependence on the initial Li electrodeposition mechanism. In the case of three-dimensional nucleation, the nucleation rate , and the total number of nuclei , are expressed by the following equations:

= exp −

,

(1)

= (),

(2)

where is the electrode surface area and is the overpotential. In the case of heterogeneous nucleation of hemispherical nuclei, K1 and K2 are expressed as:10 =

%&!'

= (

!

"#

"#

/

,

,

(3) (4)

where ) is the valence of the metal ions, * is the elementary charge, is the number density of nucleation sites on the electrode surface, + is the atomic volume, , is the exchange current density, - is the Boltzmann constant, . is the temperature, and is the surface energy of the nuclei. Equation (1) indicates that the nucleation rate increases exponentially with the overpotential. In the case of galvanostatic electrodeposition, the overpotential is time-dependent and a function of the current density that flows during the electrochemical processes.11 The total current density is expressed as:

, = ,/ + ,1 + 2 ∑ 45 ,

(5)

where ,/ is the current density in the electric double-layer, ,1 is the current density for adatom adsorption, and 45 is the current density for nuclei growth. For galvanostatic electrodeposition, Eq. (5) can be rewritten as:12


15


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

7

78

Page 16 of 25

, = 67 7 + )* 7 + 2 ∑ 45 ,

(6)

where 9 is the time, 67 is the specific capacity of the electric double-layer, and : is the single adatom concentration on the electrode. In the case of diffusion-controlled deposition,13 : = :

/;

/

exp (?), A (B)

@2 = @ −

√DB

(7)

,

(8)

where : is the concentration of adatoms at equilibrium, and @ and @2 are the concentrations of metal ions in the bulk phase and at the electrode surface, respectively. ? is expressed as f=ze/kT. Equations (5)-(8) yield: 7

=G

7

D( /2) ∑ EF

.

(9)

H I 18 (/; ⁄/ )KLM (1)

45 in Eq. (8) is given by the sum of the currents for nuclei growth ,5 ,13 45 = ∑ ,5 , ,5 =

7N 7

=

(10)

/ O N

!

1 − exp Q?(

N

− )R,

(11)

where is the nuclei radius and T is the diffusion coefficient for the metal ions in a solvent. The growth rate of the nuclei radius can be simultaneously calculated by: 7N 7

=

/ O N

!

1 − exp Q?(

N

− )R.

(12)

Thus, the time evolution of , , and can be calculated by solving Eq. (2), (9), and (12) along with the other equations. Considering that the crystal orientation may affect the adatom kinetics,14 the crystal orientation of the current collector has a strong effect on the concentration of adatoms at equilibrium, : . : is known to be a function of the change in chemical potential upon adsorption of an adatom, UVW7 :15 : ~ exp Q−

YZ[H "#

R.

(13)


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


UVW7 is dependent on chemical bonds with neighboring adatoms; therefore, UVW7 is expressed as UVW7 = −\ × ^ , where \ is the number of neighboring adatoms and ^ is the energy of the bond between the adatoms. This value is dependent on the crystal orientation of the current collector. In the present study, a single adatom has 3 closest neighbors on the Cu (111), while the number is 4 on the Cu (001) and 5 on Cu (101). Thus, the difference in crystal orientation of the current collector is reflected in : and the order of magnitude for these three orientations is Γ0 (101) > Γ0 (001) > Γ0 (111). In addition, the surface has a stepped structure for high-index planes. At a step, the change in chemical potential upon adatom adsorption is higher because the adatom has surplus bonds to atoms on the side of the step. Therefore, the concentration of adatoms at equilibrium is higher than that for the low index planes, i.e., Γ0 (high-index planes) > Γ0 (101) > Γ0 (001) > Γ0 (111). However, to the best of our knowledge, the values of ^ and Γ0 for Li electrodeposition on a Cu current collector are unknown. Therefore, these values were estimated based on the past studies for Ag. In the case of Ag electrodeposition, ^ is experimentally obtained as 1.5×10-20 J,16 while the energy of an Ag-Ag bond in the bulk crystal, which is calculated from thermodynamic data, is 7.9×10-20 J.17 The decrease is caused by the partial ionization and solvation of Ag in the electrolyte and similar mechanism can be applied for Li. It is thus estimated that ^ for adatoms in contact with an electrolyte is 0.2 times smaller than that for the bulk. In the case of the Cu-Li system, the bond energy in the bulk alloy can be calculated from thermodynamic data to be 4.6×10-20 J.18 Thus ^ for the Li adatom is estimated as 9.2×10-21 J. Furthermore, the ratio between : for a Li adatom on the Cu (001) plane and a Ag adatom on the Ag (001) plane can be estimated from each ^ value and Eq. (13), which leads to : (001)Li-Cu /


17


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 18 of 25

: (001)Ag-Ag = 0.24. With reference to the experimental value of : (001)Ag-Ag = 1.2×1012 cm, we obtain : (001)Li-Cu = 2.8×1011 ≈ 1011 cm-2. Finally, estimates of : (101) g 1.0×1012 cm-

2 19

2

, : (001) g 1.0×1011 cm-2, and : (111) g 1.0×1010 cm-2 were made for Li electrodeposition on

a Cu collector. The assumption is somewhat bold but the results are considered to be not too far from the actual values and are reasonable enough for qualitative analysis. Other parameter values used in the present calculations are as follows: , = 5.0 mA/cm2 (the same as the experiment); , = 3.0 mA/cm2;5 67 = 4.0×10-3 F/cm2;20 @ = 1.0 mol/L (the same as the experiment); = 2.0×10-3 cm2 (the same as the experiment); + = 2.0×10-23 cm3;21 = 3.2×10-5 J/cm2;22 T = 5.0×10-8 cm2/s;5 and = 1.0×1015 cm-2.10 For the initial conditions: (0) = 0; @2 (0) = @ ; :(0) = : ; (0) = 0; and (0) = 0 are used.


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


Figure 9. (a) Time evolution of the overpotential η, and (b) total number of nuclei Ntotal, at various equilibrium adatom concentrations. Figure 9 shows the calculated time evolution for and . The dotted line represents / , the critical overpotential for nucleation, at which the first nucleus appears on the electrode with a surface area , and can be defined by: × U9 × exp Q−

i

R = 1,

(14)

where U9 is the width of the time step. The overpotential increases immediately upon application of a current. After the overpotential exceeds the critical overpotential, nucleation occurs and the number of nuclei begins to increase. The overpotential reaches the maximum value when ∑ 45 / becomes equal to i. Once ∑ 45 / exceeds , , the overpotential starts to decrease. After the overpotential falls below the critical value / , the current is consumed only for the growth of the existing nuclei because the number of nuclei does not increase further. In terms of the effects of the crystal orientation, the interval time for nucleation becomes shorter with decreasing : , and the total number of nuclei increases. Figure 10 shows the nucleus size distribution for different adatom equilibrium concentrations at t = 2.0 s.


19


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 20 of 25

Figure 10. Li nucleus radius distribution for different adatom equilibrium concentrations at t = 2.0 s: (a) 1.0×1010, (b) 1.0×1011, and (c) 1.0×1012 cm-2. The results show that a small : results in a small mean radius and narrow nuclei size distribution. This is due to the formation of many nuclei within a short period. On the other hand, in the case of large : , it takes longer time for nucleation and the rate is relatively low. Therefore, the growth of existing nuclei proceeds at some sites while nucleation is still ongoing at other sites. Thus, the distribution of nuclei radius becomes wide for the case of large : . Finally, let us discuss lattice matching between Li and Cu, which is not taken into consideration in the present calculation. The epitaxial electrodepositions on metals can take place


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


even under large lattice mismatch.23,24 In these cases, smaller misfits are selected by means of coincide lattice. Considering the epitaxial relation, the possible lattice matching between Li and Cu is (1×1)Li(111)[-101]//(2×2)Cu(111)[-101], (1×1)Li(210)[001]//(3×1)Cu(110)[001], and (1×1)Li(001)[100]//c(2×2)Cu(001)[100]. From lattice constants of Li (0.3436 nm) and Cu (0.3615 nm),25,26 the maximum misfit is calculated as 4.9% (See Figure S1 in supporting information). This indicates that Li can nucleate epitaxially but with an influence of the mismatch-induced lattice strain. Several studies have addressed that elastic relaxation of lattice train causes size-limitation of quantum dots formation. In galvanostatic CdSe electrodeposition on Au, narrower size distribution of the precipitates is observed. There should be the same effects in the present case but it is difficult to estimate it quantitatively. Nevertheless, our numerical analysis shows qualitatively consistent with the experimental results. Thus, this effect should not be significant. However, the narrow size distribution of nuclei for the crystal zone axis, which is not well explained, could be caused by the epitaxial growth under large lattice mismatch mentioned above.

Conclusion The crystal orientation dependence of electrodeposited Li metal on a Cu current collector was investigated both experimentally and numerically. The experimental results show that the morphology of the Li precipitates is affected by the crystal orientation of the current collector, and is the most homogeneous for orientations close to (111), followed by the zone axis, and then (001). The numerical analysis suggests that the morphological variation is attributed to the dependence of the adatom concentration at equilibrium on the crystal orientation.


21


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 22 of 25

The results from this study suggest that the non-uniformity of the Li precipitates can arise even at the initial stage of electrodeposition, and the effect can be inherited for long charging times. This morphological instability is anticipated to be the origin of dendrite growth. Thus, to suppress dendritic growth in Li anodes, it is important to select a current collector that has a low adatom concentration at equilibrium. In the case of the Cu current collector, the (111)-oriented surface has been determined to be the best.

ASSOCIATED CONTENT Supporting Information. Epitaxial relationships between Li and Cu (PDF) The supporting information is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Corresponding author at: Department of Materials Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan. Email address: [email protected] (Kohei Ishikawa). Author Contributions The manuscript was written through contributions from all authors. All authors have given approval to the final version of the manuscript. †‡§These authors contributed equally. ABBREVIATIONS


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


EBSD, Electron Backscatter Diffraction; SEM, Scanning Electron Microscopy; AES, Auger Electron Spectroscopy. REFERENCES (1) Xu, W.; Wang, J.; Dong, F.; Chen, X.; Nasybulin, E.; Zhang, Y.; Chang, J. G. Energy Environ. Sci. 2014, 1, 513-537. (2) Kim, H.; Jeong, G.; Kim, Y. U.; Kim, J. H.; Park, C. M.; Sohn, H. J. Chem. Soc. Rev. 2013, 42, 9011-9034. (3) Rosso, M.; Brissot, C.; Teyssot, A.; Dolle, M.; Sainnier, L.; Tarascon, J. M.; Bouchet, R.; Lascaud, S. Electrochim. Acta 2006, 51, 5334-5340. (4) Barton, J. L.; Bockris, J. O’M. Proc. R. Soc. London, Ser. A 1962, 268, 485-505. (5) Monroe, C.; Newman, J. J. Electrochem. Soc. 2003, 150(10), A1377-A1384. (6) Cohen, Y. S.; Cohen, Y.; Aurbach, D. J. Phys. Chem. B 2000, 104(51), 12282-12291. (7) Tikekar M. D.; Choudhury, S.; Tu, Z.; Archer, L. A Nat. Energy 2016, 1, 16114-16121. (8) Itoh, S.; Yamazoe, N.; Seiyama, T. Surf. Technol. 1977, 5, 27-42. (9) Mitsuhashi, T.; Ito, Y.; Takeuchi, Y.; Harada, S.; Ujihara, T. Thin Solid Films 2015, 590, 207-213. (10) Milchev, A. In Electrocrystallization Fundamental of Nucleation and Growth; Kluwer Academic Publishers: New York, 2002 Vol.1; pp 95-98. (11) Isaev, V. A.; Grichenkova, O. V. Electrochem. Comm. 2001, 3, 500-504. (12) Isaev, V. A.; Grishenkova, O. V.; Semerikova, O. L. J. Solid State Electrochem. 2013, 17, 361-363. (13) Isaev, V. A.; Grishenkova, O. V. J. Solid State Electrochem. 2014, 18, 2383-2386. (14) Despic, A. R.; Bockris, J. O’M. J. Chem. Phys. 1960, 32, 389-402.


23


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 24 of 25

(15) Damjanovic, A.; Setty, T. H. V.; Bockris, J. O’M. J. Electrochem. Soc. 1966, 113, 429440. (16) Kaischew, R.; Budevski, E. Contemp. Physics. 1967, 5, 489-516. (17) Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.; Halow, I. J. Phys. Chem. Ref. Data, Suppl. 1982, 11 (Suppl. 2), 160. (18) Li, D.; Furtauer, S.; Cupid, D. M. Calphad: Comput. Coupling Phase Diagrams Thermochem. 2016, 53, 105-115. (19) Budevski, E.; Staikov, G.; Lorenz, W. J. Electrochemical Phase formation and Growth; VCH Publishers: New York, 1996 Vol. 1; pp 225-226. (20) Gao, P.; Zhang, C.; Wen, G. J. Power Sources 2015, 294, 67-74. (21) Ely. D. R.; Garcia, R. E. J. Electrochem. Soc. 2013, 160(4), A662-A668. (22) Perdow, J. P.; Tran, H. Q.; Smith, E. D. Phys. Rev. B 1990, 42, 11627. (23) Vertegel, Alexey, A.; Shumsky, Mark, G.; Switzer, A. Electrochim. Acta 2000, 45, 32333239. (24) Goswami, A. Trans. Faraday Soc. 1958, 54, 821-825. (25) Smith, H. G.; Berliner, R.; Jorgensen, J. D.; Nielsen, M.; Trivisonno, J. Phys. Rev. B: Condens. Matter Mater. Phys. 1990, 41, 1231-1234. (26) Van, Ingen, R. P.; Fastenau, R. H. J.; Mittemeijer, E. J. J. Appl. Phys. 1994, 76, 18711883. (27) Springholz, G.; Holy, V.; Pinczolits, M.; Bauer, G. Science 1998, 282, 734-737. (28) Golan, Y.; Hodes, G.; Rubinstein, I. J. Phys. Chem. 1996, 100, 2220-2228.


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 Use Only

Crystal orientation dependence of precipitate structure of electrodeposited Li metal on Cu current collectors *Kohei Ishikawa†, Yasumasa Ito ‡, Shunta Harada †§, Miho Tagawa†§, Toru Ujihara†§

Synopsis: Relation between the crystal orientation of the Cu current collector and the shape of Li precipitates. Compared with the case of high index plane, precipitates on the (111) plane of the Cu collector tend to be homogeneous.


25

Crystal Orientation Dependence of Precipitate Structure of

Recommend Documents