Hydrophobic Ni-rich Layered Oxides as Cathode Materials for Lithium

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Hydrophobic Ni-rich Layered Oxides as Cathode Materials for Lithium-ion Batteries Sung Wook Doo, Suyeon Lee, Hanseul Kim, Jin H. Choi, and Kyu Tae Lee ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00786 • Publication Date (Web): 16 Aug 2019 Downloaded from pubs.acs.org on August 17, 2019

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ACS Applied Energy Materials

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Hydrophobic Ni-rich Layered Oxides as Cathode

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Materials for Lithium-ion Batteries

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Sung Wook Doo,† Suyeon Lee,† Hanseul Kim,† Jin H. Choi,§ Kyu Tae Lee†,*

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†

School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul

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National University, 1, Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

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§

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Republic of Korea

Korea Electric Power Corporation Research Institute, Yuseong-Gu, Daejeon 34056,

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* E-mail: [email protected]

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ACS Paragon Plus Environment

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ACS Applied Energy Materials 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

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KEYWORDS: lithium ion battery, cathode, surface engineering, hydrophobic, residual

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lithium compounds

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ABSTRACT: Ni-rich layered oxide materials have been considered as promising cathode

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materials for high energy density Li-ion batteries because of their high reversible capacity.

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One of their catastrophic failure modes is the formation of residual lithium compounds on

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the oxide surface when it is exposed to air. In this paper, it is demonstrated that water is

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essential for the formation of residual lithium at room temperature. Furthermore,

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hydrophobic LiNi0.8Co0.1Mn0.1O2 is introduced to suppress the formation of residual lithium

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because the hydrophobic surface inhibits contact between water and LiNi0.8Co0.1Mn0.1O2.

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Hydrophobic LiNi0.8Co0.1Mn0.1O2 is obtained through surface engineering using

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hydrophobic

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polydimethylsiloxane-grafted LiNi0.8Co0.1Mn0.1O2 suppresses the formation of residual

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lithium even in humid air, leading to the negligible surface degradation of

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LiNi0.8Co0.1Mn0.1O2. As a result, hydrophobic LiNi0.8Co0.1Mn0.1O2 shows excellent

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electrochemical performance even after storage in humid air for two weeks.

organic

molecules,

such

as

polydimethylsiloxane.

Hydrophobic

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Introduction

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Ni-rich layered oxide materials (Li[Ni1‒x‒yCoxMny]O2: 1‒x‒y ≥ 0.8) have been considered

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as promising cathode materials for high energy density Li-ion batteries because of their

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high reversible capacity of approximately 200 mA h g‒1.1-10 However, the electrochemical

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performance of Li[Ni1-x-yCoxMny]O2 (1-x-y ≥ 0.8) is not sufficient to meet the demands of

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commercial cathode materials. One of their catastrophic failure modes is the formation of

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residual lithium compounds on the Ni-rich layered oxide surface.11 Because the surface

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of Ni-rich oxide materials is unstable in air, the surface reacts with moisture and carbon

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dioxide when it is exposed to ambient air. This results in the formation of residual lithium

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compounds, such as Li2CO3, LiOH, and LiHCO3, on the surface. In addition, as 1‒x‒y in

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Li[Ni1‒x‒yCoxMny]O2 increases, the formation of residual lithium compounds is known to

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accelerate.12-13

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When residual lithium compounds form on the surface, some Li ions in

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Li[Ni1‒x‒yCoxMny]O2 are deintercalated and react with moisture and carbon dioxide. As a

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result, the initial charging capacity decreases with increasing amounts of residual lithium

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compounds.14-17 Residual lithium compounds also increase cell resistance, resulting in


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poor rate capability.18-19 Moreover, residual lithium compounds are irreversibly

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decomposed with the formation of a gas during charging. This causes a swollen battery,

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leading to both severe capacity fading and safety problems.20-25 In this connection, many

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research groups have focused on the removal of residual lithium compounds and

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demonstrated the resulting promising electrochemical performance.26 For example, a

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water washing process is known to be necessary for commercial Ni-rich layered oxide

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materials because this process effectively removes residual lithium compounds, which

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are highly soluble in water.27-29 However, the reduced initial charging capacity and cost

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increase due to water washing remain unresolved. Recently, surface modification and

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doping have improved the surface stability of Ni-rich oxide materials in air, resulting in

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improved electrochemical performance.30-36 In this paper, we introduced hydrophobic Ni-

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rich layered oxide materials to suppress the formation of residual lithium compounds. We

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demonstrated that water is essential for the formation of residual lithium at room

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temperature.25 Based on this fact, we obtained hydrophobic Ni-rich oxide materials

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through

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polydimethylsiloxane (PDMS).37-45 Hydrophobic Ni-rich oxide materials inhibited contact

surface

engineering

using

hydrophobic

organic

molecules,

such

as


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between water and the oxide surface, resulting in a reduced amount of residual lithium

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compounds forming on the surface. As a result, hydrophobic Ni-rich oxide materials

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remarkably showed negligible changes in the initial capacity fading, cycle performance,

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and rate capability even after storage in humid air for two weeks.

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Experimental Section

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Synthesis. LiNi0.8Co0.1Mn0.1O2 powders were synthesized through a coprecipitation

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method. NaOH was used to control the pH of an aqueous solution that dissolved

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NiSO4∙6H2O, CoSO4∙7H2O, and MnSO4∙H2O with the molar ratio of Ni:Co:Mn = 8:1:1.

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NH4OH was used as a chelating agent. LiOH were mixed with the dried precipitates (the

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molar ratio of Li/TM = 1.03). The mixture was then heated at 800 °C for 10 hours in O2.

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The heating rate and O2 flow rate were 5 °C min‒1 and 0.5 L min‒1, respectively. To obtain

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hydrophobic

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average

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polydimethylsiloxane (Alfa-Aesar, average molecular weight = 410 g mol‒1) were mixed

materials,

molecular

hydroxy-terminated

weight

=

550

g

polydimethylsiloxane mol‒1)

and

(Sigma-Aldrich,

trimethylsiloxy-terminated


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with LiNi0.8Co0.1Mn0.1O2 powders, followed by heating the mixture in Ar at 230 °C for 9

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hours using a sealed reactor.

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Storage experiment. To demonstrate the role of water in the formation of residual lithium

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compounds, LiNi0.8Co0.1Mn0.1O2 powders were stored in a continuous flow reactor for 24

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hours. Dry CO2 (99.999%), humid CO2, and humid inert Ar gases flowed through the

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reactor. The RH of the humid CO2 and humid Ar flows was ca. 74%. In addition, bare and

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PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powders were stored in a humidity chamber at

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50% RH and 25 °C to examine their electrochemical performances.

85 86

Material characterization. The XRD patterns of the powders were acquired using a D2

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Phaser with Cu-Kα radiation (λ = 1.5418 Å) operated in the 2θ range of 10° – 80°. SEM

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was performed using a field emission scanning electronic microscope (Carl Zeiss,

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Auriga). TEM and EDS data were collected using a Cs-corrected scanning transmission

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electron microscope (JEOL Ltd, JEM-ARM200F). Cross-sectional TEM specimens were

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prepared with a FIB system. Before FIB milling, samples were coated with carbon and


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platinum. FT-IR spectra were collected on a FT-IR spectrometer (Bruker, TENSOR27).

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TGA was performed with a simultaneous DTA/TGA analyzer (TA instruments, DTA) under

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an air atmosphere with a heating rate of 10 °C min‒1. Contact angles were measured with

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a contact angle meter (KRUSS, DSA100). Pellets were prepared using 0.3 g of powders

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at 45 MPa for 30 minutes for the contact angle measurements. TOF-SIMS analyses were

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performed on a TOF-SIMS 5 system with a Bi+ primary ion beam source (ION-TOF

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GmbH, Germany). A pulsed 25 keV Bi+ beam was used as an analysis source. A 14.5

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keV Cs+ (negative mode) ion beam was used for sputtering with a raster size of 200 μm

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× 200 μm. Depth profiles were obtained with a raster size of 50 μm × 50 μm. Titrations

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were carried out with a pH meter (Thermo Fischer, ORION STAR A211). For a titration,

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1.5 g of LiNi0.8Co0.1Mn0.1O2 powders were washed in distilled water for one hour. A 0.03

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N HCl solution was used as a titrant.

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Electrochemical characterization. Samples of active materials were mixed with carbon

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black (Super P) and polyvinylidene fluoride in a weight ratio of 8:1:1. The slurry was

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casted onto an Al foil current collector. The mass loading of active materials was 2.2–2.4


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mg cm−2. The cycle performance of LiNi0.8Co0.1Mn0.1O2 was evaluated in a voltage range

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of 3.0−4.4 V vs Li/Li+ at 0.5 C rate (100 mA g−1) after precycling at 0.1 C rate.

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Galvanostatic experiments were carried out using 2032 coin cells with a Li metal and 1.3

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M LiPF6 in ethylene carbonate:ethyl-methyl carbonate:dimethyl carbonate (3:4:3 volume

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ratio, Soulbrain Co. Ltd.) at 30 °C.

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Results and Discussion

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LiNi0.8Co0.1Mn0.1O2 powders were obtained through a co-precipitation method. Figure S1

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shows the X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) image

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of the LiNi0.8Co0.1Mn0.1O2 powders. This reveals that the LiNi0.8Co0.1Mn0.1O2 powders

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were 2‒4 µm in size and had no impurities. In order to investigate the role of water in the

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formation of residual lithium compounds, we compared the formation of residual lithium

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compounds on the surface after storage in three different atmospheres: (i) dry CO2

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without H2O, (ii) humid CO2 with a relative humidity (RH) of ca. 74%, and (iii) humid inert

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Ar with a relative humidity (RH) of ca. 74%. Figure 1a shows the magnified SEM image

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of a bare LiNi0.8Co0.1Mn0.1O2 particle, the surface of which is clean and smooth. We stored


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these fresh LiNi0.8Co0.1Mn0.1O2 powders in dry CO2, humid CO2 and humid inert Ar

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atmospheres for 24 hours. We then observed remarkable difference in their SEM images,

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as shown in Figure 1b, 1c, and 1d. While the surfaces of LiNi0.8Co0.1Mn0.1O2 stored in dry

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CO2 and humid Ar remained smooth after the storage (Figure 1b and 1c), a rough surface

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was observed on the LiNi0.8Co0.1Mn0.1O2 stored in humid CO2 (Figure 1d).

129


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Figure 1. SEM images of a bare LiNi0.8Co0.1Mn0.1O2 particle: (a) before storage, (b) after

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storage in dry CO2 for one day, (c) after storage in humid inert Ar for one day, and (d)

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after storage in humid CO2 for one day. (e) The amounts of residual lithium compounds

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on the LiNi0.8Co0.1Mn0.1O2 surface measured from titration.


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The small particles that formed on the surface are known to be residual lithium compounds.13, 30

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This reveals that residual lithium formed only in a humid CO2 environment. We also

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performed pH titration to measure changes in the amount of residual lithium compounds

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before and after the storage. As shown in Figure 1e, the total amount of residual lithium

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compounds substantially increased after storage in humid CO2, whereas negligible

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increases in residual lithium compounds were measured after storage in dry CO2 and in

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humid Ar. This is consistent with the SEM results in Figure 1, and this implies that both

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water and CO2 are essential for the formation of residual lithium compounds at room

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temperature. Therefore, it is anticipated that the hydrophobic surface of Ni-rich layered

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oxides suppresses the formation of residual lithium compounds because the hydrophobic

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surface inhibits contact between water and Ni-rich layered oxides, as shown in Figure 2.

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Figure 2. Schematic concept of hydrophobic Ni-rich layered oxides.

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We obtained the hydrophobic LiNi0.8Co0.1Mn0.1O2 powders through surface engineering

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using hydrophobic organic molecules, such as the vapor deposition of hydroxy-terminated

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PDMS (denoted as PDMS(-OH)). PDMS is known as a hydrophobic molecule.46-50 When

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the mixture of LiNi0.8Co0.1Mn0.1O2 and PDMS was heated in a sealed reactor at 230 °C,

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vaporized PDMS reacted with the LiNi0.8Co0.1Mn0.1O2 surface, forming M-O-Si bonding

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(M = transition metals such as Ni, Co, and Mn).51-52 In more detail, the hydroxyl functional

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groups of PDMS reacted with the hydroxyl groups on the oxide surface through a

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condensation reaction with loss of H2O. LiNi0.8Co0.1Mn0.1O2 powders were grafted with

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two different amounts of hydroxy-terminated PDMS: ca. 4 wt% and ca. 5 wt% PDMS(-


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OH)-grafted LiNi0.8Co0.1Mn0.1O2, as shown in the thermogravimetric analysis (TGA)

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profiles (Figure 3). Figure 4a shows the cross-sectional scanning transmission electron

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microscopy (STEM) and the corresponding energy dispersive X-ray spectroscopy (EDS)

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mapping images of ca. 4 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2. Cross-sectional

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STEM specimens were obtained using a focused ion beam (FIB) system. The STEM

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image shows that a thin layer was uniformly coated on the LiNi0.8Co0.1Mn0.1O2 surface. Si

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atoms were observed in the thin coating layer, as shown in the corresponding EDS

167

mapping image. This implies that the thin coating layer is PDMS because PDMS contains

168

Si atoms. The uniform coating of PDMS is also supported by the SEM images of PDMS(-

169

OH)-grafted LiNi0.8Co0.1Mn0.1O2 particles (Figure S2).

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In addition, we obtained the EDS line profiles of Si and Ni atoms near the

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LiNi0.8Co0.1Mn0.1O2 surface to estimate the thickness of the PDMS coating layers. As

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shown in Figures 4c and 4d, the thicknesses of PDMS coating layers were approximately

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30 nm and 50 nm for ca. 4 wt% and ca. 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2

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particles, respectively. Fourier-transform infrared spectroscopy (FT-IR) analysis also

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supports that PDMS molecules were coated on the LiNi0.8Co0.1Mn0.1O2 surface. As shown


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176

in Figure 5, the characteristic IR bands of PDMS were observed in the IR spectra of 4

177

wt% PDMS(-OH)-grafted and 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powders,

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which are located near 1014 cm-1 and 1087 cm-1 for Si-O-Si and near 799 cm-1 and 1258

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cm-1 for CH3-Si.53-54

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Figure 3. TGA profiles of bare, PDMS(-CH3)-grafted, 4 wt% PDMS(-OH)-grafted, and 5

183

wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powders.


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Figure 4. Cross-sectional STEM and EDS mapping images of (a) 4 wt% PDMS(-OH)-

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grafted and (b) PDMS(-CH3)-grafted LiNi0.8Co0.1Mn0.1O2. EDS line profiles of (c) 4 wt%

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and (d) 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powders.


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Figure 5. FT-IR spectra of bare, PDMS(-CH3)-grafted, 4 wt% PDMS(-OH)-grafted, and 5

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wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powder samples.

192 193 194

Moreover, we performed the vapor deposition of trimethylsiloxy-terminated PDMS

195

(denoted as PDMS(-CH3)) on the LiNi0.8Co0.1Mn0.1O2 surface to demonstrate the chemical

196

bonding between PDMS(-OH) and LiNi0.8Co0.1Mn0.1O2. 4 wt% of PDMS(-CH3) was mixed

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with LiNi0.8Co0.1Mn0.1O2 powders, followed by heating the mixture at 230 °C. In contrast

198

to PDMS(-OH), negligible amount of PDMS(-CH3) was coated on the LiNi0.8Co0.1Mn0.1O2


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surface, as shown in the TGA profile of PDMS(-CH3)-grafted LiNi0.8Co0.1Mn0.1O2 (Figure

200

3). This is also supported by the cross-sectional STEM and EDS mapping images and

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FT-IR spectrum of PDMS(-CH3)-grafted LiNi0.8Co0.1Mn0.1O2. As shown in the cross-

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sectional STEM and EDS mapping images of PDMS(-CH3)-grafted LiNi0.8Co0.1Mn0.1O2,

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Si was not observed on the LiNi0.8Co0.1Mn0.1O2 surface (Figure 4b). In addition, the

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characteristic IR bands of PDMS were faintly observed in the IR spectrum of PDMS(-

205

CH3)-grafted LiNi0.8Co0.1Mn0.1O2 powders (Figure 5). Therefore, this implies that PDMS(-

206

OH) was grafted on the LiNi0.8Co0.1Mn0.1O2 surface through the M-O-Si bonding (M =

207

transition metals such as Ni, Co, and Mn) whereas PDMS(-CH3) was not grafted on

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LiNi0.8Co0.1Mn0.1O2. This is attributed to the fact that PDMS(-CH3) does not have the

209

hydroxyl functional groups that can react with the hydroxyl groups on the oxide surface.

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The contact angles of water droplets were measured to evaluate the hydrophobicity of

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the PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2. Figure 6 compares the contact angles of

212

bare and PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 pellets. In the case of bare

213

LiNi0.8Co0.1Mn0.1O2, the pellet absorbed a water droplet as soon as it fell. Consequently,

214

we were not able to measure the contact angle of bare LiNi0.8Co0.1Mn0.1O2, as shown in


18

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Figure 6a. This implies that the surface of bare LiNi0.8Co0.1Mn0.1O2 is hydrophilic.

216

However, the contact angle of PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 increased with

217

increasing amounts of the PDMS coating, as shown in Figure 6b and 6c. The contact

218

angles of ca. 4 wt% and ca. 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 were 55° and

219

86°, respectively. This reveals that PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powders are

220

hydrophobic.

221

hydrophobic with increasing amounts of the PDMS coating.

Moreover,

PDMS(-OH)-grafted

LiNi0.8Co0.1Mn0.1O2

became

more

222

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis was performed

223

to demonstrate the role of a hydrophobic surface in the formation of residual lithium

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compounds. Bare, ca. 4 wt% PDMS(-OH)-grafted, and ca. 5 wt% PDMS(-OH)-grafted

225

LiNi0.8Co0.1Mn0.1O2 powders were stored in a humidity chamber at 50% RH and 25 °C for

226

one week. Then, the TOF-SIMS depth profiles of the LiCO3- ions were obtained, as shown

227

in Figure 7. Whereas we observed a large amount of LiCO3- ions near the bare

228

LiNi0.8Co0.1Mn0.1O2 surface after the storage, negligible amounts of LiCO3- ions were

229

measured near the surfaces of ca. 4 wt% and ca. 5 wt% PDMS(-OH)-grafted

230

LiNi0.8Co0.1Mn0.1O2.

This

indicates

that

PDMS(-OH)-grafted

LiNi0.8Co0.1Mn0.1O2


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231

suppressed the formation of residual lithium compounds on the surface because the

232

hydrophobic surface inhibited contact between LiNi0.8Co0.1Mn0.1O2 and water.

233


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234 235

Figure 6. Contact angles of (a) bare, (b) 4 wt% PDMS(-OH)-grafted, and (c) 5 wt%

236

PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 pellets.

237 238


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Figure 7. TOF-SIMS depth profiles of LiCO3- for bare, 4 wt% PDMS(-OH)-grafted, and 5

241

wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 powder samples after storage in a humidity

242

chamber at 50% RH and 25 °C for one week.

243 244

Figures 8 and S3 compare the cycle performances and voltage profiles of bare, ca. 4

245

wt% PDMS(-OH)-grafted, and ca. 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2

246

electrodes before and after storage in a humidity chamber at 50% RH and 25 °C. In the

247

case of the bare LiNi0.8Co0.1Mn0.1O2, we observed substantially reduced initial reversible

248

capacity and poorer cycle performance after the storage. This is attributed to the fact that

249

residual lithium compounds continuously increased cell impedance during cycling


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250

because of their irreversible decomposition. However, remarkably, negligible changes in

251

the initial reversible capacity and cycle performance over 200 cycles were observed for

252

the PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 even after storage in humid air for two weeks.

253

This is due to the fact that the hydrophobic surface of PDMS(-OH)-grafted

254

LiNi0.8Co0.1Mn0.1O2 suppressed the formation of residual lithium compounds. Table S1

255


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256 257

Figure 8. Cycle performances of (a) bare, (b) 4 wt% PDMS(-OH)-grafted, and (c) 5 wt%

258

PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 electrodes at a 0.5 C rate (100 mA g−1) before

259

and after storage in a humidity chamber at 50% RH and 25 °C.


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260 261

Figure 9. Rate performances of (a) bare, (b) 4 wt% PDMS(-OH)-grafted, and (c) 5 wt%

262

PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 electrodes before and after storage in a humidity

263

chamber at 50 % RH and 25 °C.


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264 265

summarized the capacity retentions of bare, 4 wt%, and 5 wt%-PDMS(-OH)-grafted

266

electrodes before and after storage in humid air. Moreover, we compared the rate

267

performance of bare, ca. 4 wt% PDMS(-OH)-grafted, and ca. 5 wt% PDMS(-OH)-grafted

268

LiNi0.8Co0.1Mn0.1O2 electrodes before and after storage (Figure 9). Before the storage,

269

bare LiNi0.8Co0.1Mn0.1O2 delivered 77.3% of the reversible capacity at 5 C rate compared

270

to the reversible capacity at 0.1 C rate. However, after storage for two weeks, bare

271

LiNi0.8Co0.1Mn0.1O2 delivered only 66.9% of the reversible capacity at 5 C rate compared to the

272

reversible capacity at 0.1 C rate. This reveals that the cell impedance of bare LiNi0.8Co0.1Mn0.1O2

273

increased during storage, resulting in a ca. 10% loss of the reversible capacity at 5 C rate after the

274

storage. However, PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2 showed negligible changes in rate

275

performance before and after the storage. This is consistent with the cycle performances of bare,

276

ca. 4 wt% PDMS(-OH)-grafted, and ca. 5 wt% PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2

277

electrodes (Figure 8).

278 279

Conclusions

280

We introduced hydrophobic Ni-rich layered oxides as promising cathodes for Li-ion

281

batteries. The hydrophobic surface of Ni-rich layered oxides was obtained through


26

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282

surface engineering using hydrophobic organic molecules, such as PDMS. The hydroxy-

283

terminated PDMS reacted with the hydroxyl group on the LiNi0.8Co0.1Mn0.1O2 surface

284

through a condensation reaction with loss of H2O at 230 °C. STEM and EDS analyses

285

revealed that PDMS layers were uniformly coated on the LiNi0.8Co0.1Mn0.1O2 surface. The

286

thicknesses of the PDMS coating layers were 30 ‒ 50 nm, depending on the weight ratio

287

of PDMS and LiNi0.8Co0.1Mn0.1O2. Through the comparison of the LiNi0.8Co0.1Mn0.1O2

288

surface after storage in various atmospheres, we demonstrated that H2O is essential for

289

the formation of residual lithium compounds at room temperature. The hydrophobic

290

surface of LiNi0.8Co0.1Mn0.1O2 prevented contact between H2O and LiNi0.8Co0.1Mn0.1O2.

291

Therefore, hydrophobic LiNi0.8Co0.1Mn0.1O2 suppressed the formation of residual lithium

292

compounds in humid air, leading to negligible surface degradation even during storage in

293

humid air for two weeks. As a result, hydrophobic PDMS(-OH)-grafted LiNi0.8Co0.1Mn0.1O2

294

showed excellent electrochemical performance even after storage in humid air for two

295

weeks.

296

We also believe that hydrophobic surface modification can improve the storage stability

297

and electrochemical performance of other H2O-sensitive cathode materials, such as


27


Page 28 of 42

298

lithium-rich transition metal oxides for Li-ion batteries and sodium transition metal oxides

299

for Na-ion batteries.

300 301 302

■ ASSOCIATED CONTENT

303

Supporting Information

304

The supporting information is available free of charge via the Internet at

305

http://pubs.acs.org.

306

XRD patterns, SEM images, voltage profiles, and the table of capacity retention.

307 308

■ AUTHOR INFORMATION

309

Corresponding Author

310

* E-mail : [email protected]

311

Notes


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312


The authors declare no competing financial interest.

313 314

■ ACKNOWLEDGMENT

315

This work was supported in part by the National Research Foundation of Korea (NRF)

316

grant funded by the Korea government (MSIT) (2019R1A2B5B03070673 and NRF-

317

2018R1A5A1024127), and by Technology Development Program to Solve Climate

318

Changes (NRF-2018M1A2A2063345) through NRF funded by Ministry of Science and

319

ICT.

320 321

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Hydrophobic Ni-rich Layered Oxides as Cathode Materials for Lithium

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