Lawrence Berkeley National Laboratory
Recent Work
Title
Challenges for and Pathways toward Li-Metal-Based All-Solid-State Batteries
Permalink
https://escholarship.org/uc/item/8hx0140n
Journal
ACS Energy Letters, 6(4)
ISSN
2380-8195
Authors
Albertus, P
Anandan, V
Ban, C
et al.
Publication Date
2021-04-09
DOI
10.1021/acsenergylett.1c00445
Peer reviewed
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University of California
CHALLENGES FOR AND PATHWAYS TOWARD LI-METAL BASED ALL SOLID-
STATE BATTERIES
Paul Albertus
a
, Venkataramani Anandan
b
, Chunmei Ban
c
, Nitash Balsara
d
,
Ilias Belharouak
e
,
Zonghai Chen
f
, Claus Daniel
e
, Marca Doeff
g
, Nancy. J. Dudney
e
,* Bruce Dunn
h
, Josh Buettner-
Garrett
i
, Stephen J. Harris
g
, Subramanya Herle
j
, Eric Herbert
k
, Sergiy Kalanus
e
, Joesph Libera
l
,
Dongping Lu
m
, Steve Martin
n
, Matthew T. McDowell
o
, Bryan McCloskey
d
, Y. Shirley Meng
p
,
Jagjit Nanda
e
,* Jeff Sakamoto
q
, Ethan C. Self
e
, Sanja Tepavcevic
f
, Eric Wachsman
a
, Chunsheng
Wang
a
, Andrew S. Westover
e
, Jie Xiao
m
, Thomas Yersak
r
Solid-state batteries utilizing Li metal anodes have the potential to enable improved
performance (specific energy >500 Wh/kg, energy density >1,500 Wh/L), safety, recyclability,
and potentially lower cost (< $100/kWh) compared to advanced Li-ion systems.
1, 2
These
improvements are critical for the widespread adoption of electric vehicles and trucks and could
create a short haul electric aviation industry.
1-3
Expectations for solid-state batteries are high, but
there are significant materials and processing challenges to overcome.
On May 15
th
, 2020, Oak Ridge National Laboratory (ORNL) hosted a 6-hour, national
online workshop to discuss recent advances and prominent obstacles to realizing solid-state Li
metal batteries. The workshop included more than 30 experts from national laboratories,
universities, and companies, all of whom have worked on solid-state batteries for multiple years.
The participants’ consensus is that, although recent progress on solid-state batteries is exciting,
much has yet to be researched, discovered, scaled, and developed. Our goal was to examine the
issues and identify the most pressing needs and most significant opportunities. The organizers
asked workshop participants to present their views by articulating fundamental knowledge gaps
for materials and processing science, mechanical behavior and battery architectures critical to
advancing solid-state battery technology. The organizers used this input to set the workshop
agenda. The group also considered what would incentivize the adoption of US manufacturing
and how to accelerate and focus research attention for the benefit of the US energy, climate, and
economic interests. The participants identified pros and cons for sulfide, oxide, and polymer-
based solid-state batteries and identified common science gaps among the different chemistries.
Addressing these common science gaps may reveal the most promising systems to pursue in the
future.
Figure 1: Schematic summarizing the critical gaps for the realization of
competitive solid-state batteries. The workshop highlighted specific
challenges in Materials Science, Processing Science, and Design
Engineering.
A comprehensive document was drafted and published as an ORNL technical document
(doi:10.2172/1731043).
4
The document reports a consensus of the most essential considerations
to enable low-cost, safe, high-performance, long-lasting, and scalable solid-state batteries. As
shown in Figure 1, this focus article summarizes the following main findings of the workshop
(see the ORNL technical document for more details):
I. Materials Science Gaps
II. Processing Science Gaps
III. Design Engineering Gaps
Although not stated as specific goals for the workshop, participants also addressed practical
tradeoffs in manufacturing processes and efficiency, materials costs and handling, and
environmental sensitivity. Discussions touched on opportunities and barriers for domestic battery
manufacturing. Participants agreed that testing standardization and statistical analysis of solid-
state battery performance are critical to advance the field.
5
Currently, reported properties and cell
performance vary unacceptably among laboratories studying nominally the same materials. A
careful safety evaluation is also needed to quantify solid-state battery safety versus that of
leading Li-ion designs, including the important issue of whether a small amount of liquid may
be added to improve performance without compromising safety and other benefits.
To complement the workshop discussion and assess state-of-the-art developments, the organizers
performed a literature analysis of solid-state batteries. Figure 2a shows the number of peer-
reviewed publications over the timespan 2000-2020. The volume of literature and rate of
publication has increased significantly over the last decade. To ensure a representative
perspective, a dozen recent review articles were analyzed based on their emphasis on key
technical areas for solid-state battery development (see Figure 2b).
5-16
The analysis revealed that
researchers have made significant progress in new materials discovery, but integrating these
materials into practical devices has lagged. The dearth of relevant prototype cell data may be
due to an underemphasis on processing science and solid-state mechanics, as well as the
challenges for the single-PI research model to overcome the challenges in producing high-quality
prototype cells. This analysis is consistent with the discussions held during the workshop.
Figure 2. Solid-state battery literature analysis showing (a) peer-reviewed publications from
2000 to 2020 (keywords: lithium and solid-state battery*, Web of Science) and (b) a radar plot
that compares the level of activities in key technical areas for solid-state batteries based on
analysis of 12 recent review articles.
5-16
I. MATERIALS SCIENCE GAPS
Progress on solid-state batteries surges following the discovery of promising solid electrolytes.
However, every known solid electrolyte has one or more drawbacks that must be overcome to
enable the development of viable solid-state batteries for EVs. Work should continue to discover
new electrolytes, with the expectation that other performance and processing criteria are
simultaneously satisfied. Furthermore, a clear understanding of the challenges to integrating
components into batteries will inform the search for new materials.
I.1 Science Gaps for the Li metal anode
The Li metal anode is common to all the batteries considered at the workshop, yet this
component may be the least studied. Li metal has recently captured more attention from the US
Department of Energy (DOE) Vehicle Technologies Office and the Advanced Research Projects
Agency-Energy (ARPA-E). There was considerable discussion among participants on this topic.
“We know so much more now than just 5 years ago, but we are just getting started,” reported
Paul Albertus from the University of Maryland. One key finding, by nanoindentation and
compression of Li micropillars, is that when the volume of Li is small, the hardness and yield
strength can be much larger than that of bulk Li.
17, 18
Consequently, we need to determine the
relevant length scale for mechanical tests to inform our understanding of the Li anode and the
mechanisms leading to Li redistribution, particularly when related to battery failure
The following questions need to be answered to fill the science gaps that exist in the
development of an optimized Li metal anode:
What defect generation/annihilation processes operate in Li films (< 30 µm thick)
when Li is plated and stripped through a generic solid electrolyte?
What conditions (e.g., rate, temperature, applied stress, and duty cycle history)
modify Li plating and stripping behavior?
What are the stress relaxation mechanisms for Li, and how do they change with the
type and magnitude of the stress field, the mechanical boundary conditions, and the
strain rate?
How do defects such as grain boundaries, dislocation density, elemental impurities,
and alloying elements alter the properties and cycling performance of Li metal
anodes?
Is a Li seed layer needed to template plated Li or provide mechanical compliance to
impove cycling stability?
How do interphase regions, formed by reactions or additions at the Li/solid
electrolyte interface, govern transport?
I.2 Science Gaps for the Solid Electrolyte in Contact with Li Metal
The community has learned much about failure at the Li/solid electrolyte interface in recent
years. More specifically, we see that (1) effective passivation of the interface reduces Li
consumption, (2) a high modulus solid electrolyte formed with a dense, smooth interface suffers
fewer issues related to Li roughening, (3) a higher fracture toughness inhibits cracks that may
form shorts, and (4) higher electronic resistivity mitigates Li
+
reduction within the solid
electrolyte separator. Given this background, several important questions were identified:
What promotes electrochemical stability or kinetically-limited passivation with Li?
What mechanisms are available to strengthen solid electrolyte properties at the
appropriate length scale, improve stability, and inhibit failures/fatigue during
extended Li cycling?
How do the bulk properties of the solid electrolyte and its surface
chemistry/homogeneity (e.g., current uniformity) affect Li cycling?
