Article category: Full Paper
Subcategory: Lithium Ion Batteries
Dual additives for stabilizing Li deposition and SEI formation in
anode-free Li metal batteries
Baolin Wu, Chunguang Chen,* Dmitri L.
Danilov,* Zhiqiang Chen, Ming Jiang, Rüdiger-A. Eichel
and Peter H.L. Notten*
Baolin Wu, Dr. Chunguang Chen, Dr. Dmitri L. Danilov, Prof. Rüdiger-A.
Eichel, Prof. Peter H.L. Notten
Forschungszentrum Jülich (IEK-9), D-52425, Jülich, Germany;
Baolin Wu, Prof. Rüdiger-A. Eichel
RWTH Aachen University, D-52074 Aachen, Germany.
Dr. Chunguang Chen
LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing
100190, China;
School of Engineering Sciences, University of Chinese Academy of
Sciences, Beijing 100049, China.
Dr. Dmitri L. Danilov, Dr. Zhiqiang Chen, Prof. Peter H.L. Notten
Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The
Netherlands.
Dr. Ming Jiang
Insitute of Crabon Neutrality and New Energy, School of Electronics and
Information, Hangzhou Dianzi University, Hangzhou 310018, China.
Prof. Peter H.L. Notten
University of Technology Sydney, Broadway, Sydney, NSW 2007, Australia
E-mail:
p.h.l.notten@tue.nl ;
chenchunguang@imech.ac.cn;
D.Danilov@tue.nl
Keywords : Dual-additives, Li growth, SEI formation, anode-free
lithium metal battery, in situ Raman
Abstract. Anode-free Li-metal batteries (AFLBs) are of
significant interest to energy storage industries due to their
intrinsically high energy. However, the accumulative Li dendrites and
dead Li continuously consume active Li during cycling. That results in a
short lifetime and low Coulombic efficiency (CE) of AFLBs. Introducing
effective electrolyte additives can improve the Li deposition
homogeneity and solid-state interphase (SEI) stability for AFLBs.
Herein, we reveal that introducing dual additives, composed of
LiAsF6 and FEC, into a commercial carbonate electrolyte
will boost the cycle life and average CE of NCM||Cu
AFLBs. The NCM||Cu AFLBs with the dual additives
exhibit a capacity retention of about 75% after 50 cycles, much higher
than those with bare electrolytes (35%). The average CE of the
NCM||Cu AFLBs with additives can maintain 98.3% over
100 cycles. In contrast, the average CE without additives rapidly
decline to 97% after only 50 cycles. In situ Raman measurements
reveal that the prepared dual additives facilitate denser and smoother
Li morphology during Li deposition. The dual additives significantly
suppress the Li dendrite growth, enabling stable SEI formation on anode
and cathode surfaces. Our results provide a broad view of developing
low-cost and high-effective functional electrolytes for high-energy and
long-life AFLBs.
1. Introduction
Lithium-ion batteries (LIBs) have become the critical component and
technology limiting the driving range of electric vehicles
(EVs).[1] Boosting the energy density of LIBs will
certainly lengthen EVs’ range. Li metal is regarded as the most
attractive negative electrode for high-energy batteries due to its high
theoretical specific capacity (3860 mAh·g-1) and low
redox potential (-3.04 V vs. standard hydrogen
electrode).[2, 3] However, Li metal anode commonly
suffers from intensive side reactions, low Coulombic efficiency (CE),
and rapid capacity fading. These problematic issues originate from Li
dendrite growth during Li plating/stripping and the continuous formation
of solid electrolyte interphase (SEI), which consumes cyclable
lithium.[4-6] Additionally, Li metal batteries
often use thick Li metal foils at the anode side, which reduces
batteries’ energy density and causes safety
concerns.[7]
Anode-free Li metal batteries (AFLBs) with current-collector
(Cu)||electrolyte||cathode||current-collector
cell configuration can be used to overcome the drawbacks of conventional
Li metal battery systems.[8, 9] In AFLBs, the
cathode offers active Li source for being plated on the Cu or other type
of current-collector substrate. In this sense, no excess of Li metal is
present in pristine AFLBs.[10, 11] The absence of
Li metal anode leads to less weight, less volume, lower manufacturing
costs, and therefore higher energy density than conventional Li metal
batteries.[12, 13] The anode-free design was
previously considered impractical due to the short cycle life and low
CE, caused by unstable SEI formation, Li dendrites, and dead Li
metal.[9] The Li source in AFLBs is only provided
by the cathode material. Therefore the formation of SEI and dead Li
metal rapidly consume cyclable Li-ions, drastically decreasing battery
capacity.[8] The CE of Li deposition must be
considered while developing practical AFLBs to achieve high energy
density and recyclability.
Electrolyte engineering effectively improves the CE by manipulating the
Li deposition growth and the SEI composition.[14]In fact, engineering electrolyte is an elaborate combination of several
methods, including altering organic solvents and salt chemistry, adding
additives, and manipulating concentrations of all components.
Introducing a functional additive is the most promising among these
electrolyte engineering methods. This method can effectively control
lithium metal’s plating/exfoliation behavior and modify the SEI layer’s
chemistry. Additives are applied in trace doses (usually less than 5%),
making balancing the performance and cost easier.[15,
16] Electrolyte additives can be categorized into two groups:
inorganic additives such as
LiNO3[17] and
AlCl3[18], and organic additives
like vinylene carbonate (VC)[19] and
fluoroethylene carbonate (FEC).[20] The
fluorine-containing electrolyte additives have superior kinetic
reactivity, which facilitates the formation of more LiF components in
the SEI layers to improve stability.[21] FEC is
one of Li metal batteries’ most celebrated electrolyte additives. It
forms a stable yet elastic LiF-rich SEI on Li
metal.[22] Recently, many fluorine-containing
salts have also been explored as additives, such as
LiBF4 and
LiAsF6.[23] However, in contrast
with Li metal batteries, a single additive is insufficient for effective
application in AFLBs due to the complexity of electrochemical processes
involved. Therefore, exploring suitable additives for anode-free systems
is essential for developing high-performance batteries.
Herein, a facile and effective dual additive of LiAsF6and FEC in a commercial carbonate electrolyte (1M
LiPF6-EC/DEC/DMC (1:1:1 vol%)) is reported. The
proposed dual additive enhances the electrochemical performance of the
AFLBs using NCM532 as the cathode and bare Cu foil as the anode current
collector. The NCM||Cu cell possesses an excellent
electrochemical performance with high-capacity retention of
~75% after 50 cycles and an average CE of
~98.3% in the presence of dual additives. In
situ Raman measurements were performed to investigate the effect of the
dual additives of LiAsF6 and FEC on the morphology of
deposited Li metal and formed SEI layers. The synergistic effect of
LiAsF6 and FEC contributes to smoother lithium plating.
It suppresses the formation of Li dendrites and dead Li metal.
Furthermore, F-rich SEI and CEI layers were observed to form on the Li
anode and NCM-cathode surfaces, facilitating the stability of anode-free
cells.