The Birth and Development of Lithium Metal Batteries
If one were to look through the periodic table for a metal that is “naturally suited” for batteries, lithium would almost certainly rank first. It is the lightest metal element found in nature and possesses an extremely low standard electrode potential (–3.045 V vs. SHE). The combination of these two properties gives lithium an exceptionally high theoretical energy density, with a theoretical specific capacity of up to 3860 mAh/g—far exceeding that of traditional battery materials such as zinc and lead.
For this reason, researchers were drawn to lithium at a very early stage, hoping to use it to create batteries with higher energy density and smaller size. However, between this ideal and practical reality lay a technological gap that was difficult to bridge.
1、The Starting Point: The Emergence of Non-Aqueous Electrolytes
The fundamental problem with lithium is that it does not behave “obediently” in aqueous systems. Because of its extremely low standard reduction potential, metallic lithium is thermodynamically highly unstable in water, making conventional aqueous electrolytes completely unsuitable. What truly made lithium batteries possible was the development of non-aqueous electrolyte systems.
In 1958, W. Harris of the University of California systematically investigated the electrochemical behavior of cyclic ester solvents (such as propylene carbonate, PC) in his doctoral dissertation. This work is widely regarded as one of the earliest starting points of lithium battery research. Gradually, researchers came to realize that if a suitable non-aqueous electrolyte could be found, metallic lithium might be “tamed” in a controllable and safe manner.
2、First-Generation Lithium Batteries: From Laboratory to Application
The first commercially meaningful lithium battery products emerged around 1970. Japan’s Matsushita Corporation took the lead in developing the Li/(CF)ₙ battery system, marking the transition of lithium batteries from theoretical research to practical application.
Soon, however, it became clear that Li/(CF)ₙ batteries were relatively costly and limited in overall performance. As a result, the more balanced and cost-effective Li/MnO₂ system rapidly replaced them. To this day, lithium–manganese dioxide primary batteries remain widely used in cameras, instruments, and security devices.
At the same time, other primary lithium battery systems—such as Li-I₂, Li-SOCl₂, and Li-FeS₂—also reached technological maturity. Their high energy density, low self-discharge, and long shelf life enabled primary lithium batteries to secure an irreplaceable position in medical implantable devices and military applications.
3、Two Key Breakthroughs: SEI Film and Intercalation Chemistry
The period from 1970 to 1985 is often regarded as the “golden exploratory era” in the history of lithium battery development, during which two breakthroughs occurred that profoundly influenced subsequent technologies.
The first was the proposal of the SEI (Solid Electrolyte Interphase) film.
Researchers discovered that in solvents such as PC and γ-butyrolactone, a passivation layer would spontaneously form on the surface of metallic lithium. Although this layer originates from electrolyte decomposition, it can effectively prevent continuous reactions between lithium and the electrolyte. Peled and others systematically studied the composition and mechanism of the SEI film and proposed that the rate-determining step for lithium battery performance is the migration of lithium ions through the SEI layer.
As a result, electrolyte formulation design became critically important. The design strategies that later gained widespread adoption included:
Using high-dielectric-constant solvents (such as EC) to ensure lithium salt solubility;
Adjusting SEI structure through dialkyl carbonates (such as DMC);
Introducing low-viscosity solvents (such as DME) to improve overall ionic conductivity.
The second breakthrough was the rise of intercalation compounds and intercalation chemistry.
Researchers began exploring layered chalcogenide materials as cathodes, allowing lithium ions to undergo “intercalation–deintercalation” rather than violent chemical reactions. Materials such as TiS₂ and MoS₂ were introduced in succession. Among them, Li/TiS₂ batteries demonstrated excellent cycling stability under lithium-excess conditions.
This concept of “intercalation-based reactions” laid the theoretical foundation for the later development of lithium-ion batteries.
4、Safety Issues: The Inherent Challenge of Lithium Metal
Despite the excellent performance of rechargeable lithium metal batteries, safety concerns have always been unavoidable. When lithium ions are reduced to metallic lithium at the anode, dendrites can easily form. Once these dendrites penetrate the separator and contact the cathode, the result may be a mild internal short circuit—or, in severe cases, fire or even explosion.
To address this issue, researchers explored various approaches, such as replacing pure lithium metal with Li–Al alloys, or suppressing dendrite growth through electrolyte optimization and the introduction of solid polymer electrolytes. However, due to limitations such as low room-temperature ionic conductivity and complex manufacturing processes, these solutions proved difficult to commercialize on a large scale.
5、The Turning Point: The Emergence of Lithium-Ion Batteries
The event that truly changed the direction of the industry was the explosion of a rechargeable lithium battery produced by Moli Energy in 1989. This incident forced the entire field to re-evaluate the safety risks associated with metallic lithium.
Just one year later, Sony officially launched the lithium-ion battery, adopting a “lithium-free anode” design that fundamentally eliminated the dendrite problem. From that point on, rechargeable lithium metal batteries gradually faded from the mainstream, and the era of lithium-ion batteries officially began.
6、Final Thoughts
Looking back at the development of lithium metal batteries, they represent both the starting point of lithium battery technology and the stage where safety challenges were most concentrated. The theories of SEI films, the concept of intercalation chemistry, and the deep understanding of electrolytes and interfaces all directly shaped the technological pathways of today’s lithium-ion batteries.
In this sense, without the exploration of lithium metal batteries, there would be no mature, safe, and high-performance lithium-ion battery industry as we know it today.
