Cutting edge technology of lithium-ion batteries

The rapid development of industries, aviation, defense, and other fields has put forward higher requirements for battery energy density, 

power density, safety, service life, extreme environmental applicability, and cost reduction. 

At the same time, China is also facing international competition. 

In recent years, Japan, the United States, the United Kingdom, and the European Union have proposed some national plans for batteries to strengthen basic research, 

hoping to further layout at the source and seize the high ground. 

China should strengthen basic research in the field of battery technology, enhance the development of high specific energy, 

long-life, intelligent battery materials and battery system technologies,

 attach importance to the development of emerging battery technologies such as solid-state lithium batteries, 

and achieve technological self-reliance from the source, hoping to lead the development of the new generation of batteries. 

Forward looking battery technology mainly includes innovation in battery materials, battery structure, 

advanced manufacturing/characterization technology for batteries, battery digitization, etc.

Innovation in Battery Material System

The pursuit of energy density and safety in lithium batteries is an eternal theme in battery manufacturing, 

and lithium batteries belong to the electrochemical system. 

The performance improvement and cost reduction brought by the innovation of underlying materials are more significant. 

The next generation of battery new materials includes high-capacity lithium rich manganese based positive electrode, high nickel ternary, high-voltage lithium cobalt oxide, 

nano silicon negative electrode, composite metal lithium negative electrode, and high safety solid electrolyte materials.

(1) High specific capacity lithium manganese based cathode material

Among current positive electrode materials, 

lithium rich manganese based oxides with mixed redox properties can significantly improve energy density and are considered one of the most promising candidates [2]. 

Rich lithium manganese based cathode materials can be regarded as composed of two components, Li2MnO3 and LiMO2.

 The general composition can be expressed as xLi2MnO3 (1-x) LiMO2 (0<x<1, M=transition metals such as Ni, Co, Mn, and their combinations). 

Rich lithium manganese based cathode materials have extremely high theoretical specific capacity (>350 mAh/g) and reversible specific capacity (>250 mAh/g) at high voltages (>4.5 V). 

The source of high capacity is not only the redox pairs composed of transition metal ions (usually Ni2+/Ni4+, Co3+/Co4+, 

with a small amount of Mn3+/Mn4+), but also the oxygen anion redox pairs (O2-/O -/O2) that provide additional specific capacity, achieving high specific capacity. 

Rich lithium manganese based cathode materials reduce the use of expensive Co and Ni, and compared to lithium cobalt oxide and ternary materials, 

the cost of rich lithium manganese based cathode materials is lower; At a relatively low voltage of 4.2 V, the cycle life is high, reaching over 2000 cycles. 

Recently, the research group of Li Hong and Yu Xiqian from the Institute of Physics of 

the Chinese Academy of Sciences has developed a 10 Ah grade soft packed lithium secondary battery based 

on the high capacity lithium rich manganese oxide anode and ultra-thin lithium metal anode,

with the mass specific energy reaching 711.30 Wh/kg and the volume specific energy reaching 1653.65 Wh/L [3].

(2) Composite metal lithium negative electrode structure and interface protection

The negative electrode of metal lithium batteries replaces the graphite negative electrode material of traditional lithium-ion batteries with lithium metal. 

Using metal lithium as the negative electrode is expected to significantly reduce the quality and volume of the battery, 

which is an important source of high energy density for lithium metal batteries [4]. 

From a voltage perspective, the use of metallic lithium on the negative electrode in the future can increase the voltage difference to 5 V, 

which undoubtedly brings about an improvement in battery life. 

In terms of specific capacity, the specific capacity of metallic lithium can reach 3860 mAh/g.

 In the future development of positive electrodes, high specific capacity materials such as lithium manganese based materials will also be used. 

With the advantages of their materials, they can achieve a specific energy of over 40% higher than conventional lithium batteries, reaching over 400 Wh/kg. 

Lithium metal batteries have higher theoretical specific energy when using sulfur or oxygen as the positive electrode, for example, 

the theoretical specific energy of lithium sulfur (Li-S) and lithium oxygen (Li-O2) batteries are 2600 Wh/kg and 3505 Wh/kg, respectively. 

Despite the high energy density of lithium metal batteries, 

there are still issues of short circuits and thermal runaway caused by dendrite growth during lithium deposition/stripping processes. 

To suppress the growth of lithium dendrites on the surface of lithium metal negative electrodes during charge and discharge processes, 

researchers have mainly adopted two strategies to improve lithium deposition/stripping behavior and suppress dendrite growth: 

firstly, the lithium negative electrode interface protection strategy, constructing a surface artificial SEI film;

 Next is the development of metal lithium composite negative electrodes, 

which induce dense deposition within lithium confinement and suppress dendrite growth through alloy frameworks and gradient lithium friendly elements.

(3) Silicon negative electrode

At present, graphite anode is the mainstream negative electrode for lithium-ion batteries, but it is approaching its performance limit. 

More and more silicon is being used in the negative electrode of commercially available lithium-ion batteries to improve battery energy density. 

The specific capacity of silicon carbon negative electrode materials currently commercially used is below 450 mAh/g, mainly for 3C digital applications. 

Silicon carbon negative electrode is a long-term choice direction for battery factories, 

essentially opening up the upper limit of energy density, controlling expansion rate, and improving cycle life. 

Silicon based negative electrode is regarded as an ideal negative electrode material for the next generation of lithium-ion batteries. 

The theoretical specific capacity of silicon material is as high as 4200 mAh/g, which is more than 10 times that of traditional graphite material. 

Lithium batteries using silicon-based negative electrode material can increase the specific energy by more than 8%, 

and the cost per kilowatt hour of battery can be reduced by at least 3% [5]. 

Amprius Corporation in the United States has formed a silicon nanowire array negative electrode by in-situ growing oriented silicon nanowires on the surface of a current collector. 

The structure of the silicon nanowire (array) negative electrode exhibits good reversibility during lithium extraction and has outstanding electrochemical performance. 

The specific capacity of the silicon nanowire reaches 3400 mAh/g, and the first efficiency reaches over 94% [6].

(4) Solid state electrolyte

Most lithium batteries on the market use organic liquid electrolytes, which inevitably undergo side reactions during charging and discharging, affecting battery life. 

At the same time, the safety issues caused by organic flammable electrolytes have raised public concerns about the safety of lithium batteries. 

From the perspective of product upgrade, the current liquid battery uses a high nickel positive electrode+silicon-based negative electrode system, 

and 350 Wh/kg may approach the maximum energy density of liquid batteries, making it impossible to achieve further breakthroughs. 

The use of solid-state electrolytes instead of electrolytes in all solid state batteries can adapt to materials with higher capacity, with a potential energy density of up to 500 Wh/kg. 

At the same time, it has the characteristics of high safety, providing a promising solution for the next generation of energy storage devices, 

and promoting its industrial development has become a consensus in the industry and scientific community [7]. 

Solid electrolytes can be divided into oxides, sulfides, polymers, halides, etc. 

Due to the low ionic conductivity and serious solid solid interface problems of solid-state batteries, their practical applications have encountered enormous challenges [8]. 

At present, the specific energy of the 10 Ah battery cell sample of sulfide solid-state batteries has reached 400 Wh/kg,

 and the cycling performance under pressure has reached more than 800 times, but the cycling and safety issues under no pressure or low pressure have not been solved yet [9].

(5) Composite fluid collection technology

Composite current collectors can increase the energy density of batteries by reducing thickness and weight, and due to the insulation, thermal shrinkage, 

melting and other characteristics of polymers, they can improve the safety of batteries, which has attracted a lot of attention from researchers in the industry [10]. 

Unlike traditional current collectors that use relatively pure aluminum foil and copper foil, composite current collectors are battery materials with a "sandwich" structure. 

The outer two layers are composed of copper or aluminum metal, and the middle layer is a base film made of PET, PP, or PI material. 

Professor Cui Yi's team at Stanford University has proposed an ultra lightweight polyimide based composite current collector. 

Batteries equipped with this composite current collector can achieve a 16% to 26% increase in specific energy 

and quickly self extinguish fires under extreme conditions such as short circuits and thermal runaway [11]. 

Recently, Professor Cui Yi's team has designed a novel porous current collector, 

and the soft pack battery using this current collector exhibits excellent rate performance (charging for 6 minutes, SOC increased from 0 to 54.3%). 

Composite current collectors have the advantages of low manufacturing cost, high safety, and strong compatibility. 

Batteries using composite current collectors have high energy density and long cycle life; 

Of course, there are also some disadvantages, such as low production efficiency and affecting battery output power,

 which means that the development of the industry still needs a long process. 

At present, downstream power, energy storage, and 3C digital battery manufacturers are actively promoting the industrial application layout of composite current collectors. 

Both Jike 009 and Jike 001, equipped with CATL Kirin batteries, use composite current collectors. 

The Serys Wenjie M9, which will be launched at the end of the year, may also use composite aluminum foil.

2、 Innovative structural design of batteries

The forward-looking layout of battery technology mainly involves new materials, innovative battery structures, and other aspects. 

Due to the difficulty in achieving breakthroughs in battery materials in the short term and the difficulty in significantly increasing the specific energy of batteries, 

battery technology is currently in a minimally invasive new stage. 

Through innovative battery structures, grouping efficiency can be greatly improved. 

Based on "highly integrated and simplified" product design and manufacturing, 

batteries can achieve "high specific energy, high safety, high reliability, and low cost". 

Therefore, the industry has shifted more energy from battery material innovation to battery structure innovation, 

and improving the volume utilization rate of power batteries through structural innovation has become the choice of various manufacturers.

(1) Bipolar structure design

The use of bipolar lithium secondary batteries through internal series stacking can improve the energy density of the battery. 

Toyota has developed this new electrode structure, 

which increases the range of electric vehicles by 20% compared to previous models, and fast charging can also reach within 30 minutes. 

Due to the fact that the number of parts can be controlled at around 1/5 to 1/4 of the original, it is expected that the cost can be reduced by 40%. 

The so-called bipolar structure is a structure formed by stacking current collectors that are divided into positive and negative electrodes on one side. 

In bipolar lithium secondary batteries, bipolar plates serve as carriers for the positive and negative electrodes, 

requiring both high voltage oxidation stability and reduction stability. 

This structure is not only smaller in size, but also has a larger area than the high current collectors used in HEV batteries. 

However, there are technical difficulties in accurately stacking these collectors. 

In 2023, Professor Huang Fuqiang and others developed lithium-ion batteries and bipolar solid-state battery soft pack devices with all aluminum current collection. 

The maximum charging voltage tested reached 7.6 V, with a specific energy of about 310 Wh/kg, and achieved stable cycling for more than 1200 hours [12].

(2) 4680 cylindrical battery

In the evolution of battery cell structure, the trend of high-capacity battery cell development has become the mainstream consensus. 

Compared to the commonly used 18650 or 21700 cylindrical batteries, 

Tesla's 4680 battery (46 mm diameter, 80 mm axial length) exhibits higher energy and power advantages [13]. 

In terms of battery cell design, with only changes in external dimensions, the cost of 4680 battery per kWh is reduced by about 14% compared to 21700. 

The power of a single battery cell increases by 5.48 times with the increase of volume, while the material used for the outer shell increases by less than 3 times. 

In the early days, cylindrical batteries established a foothold in the power market with their standardized production and unified models. 

In 2017, due to the lack of cost-effectiveness, cylindrical batteries shifted to the fields of electric tools and electric two wheelers. 

In 2020, sales of Tesla Model 3 and other models drove LG and Panasonic's cylindrical batteries to increase their domestic power battery shipments, 

and cylindrical batteries returned to the power market. 

It can be said that Tesla basically controls the development of cylindrical power batteries.

(3) Blade battery

The blade battery is designed as a single cell battery that resembles a blade in length and thickness, using a CTP non module solution. 

Due to changes in the cell structure, the design of the battery pack has also changed, 

eliminating the traditional shell structure of the battery and using the blade battery as both the beam and the cell. 

Adopting the design of honeycomb aluminum plate, two high-strength aluminum plates are pasted on both sides, with blade batteries arranged in between. 

BYD launched the lithium iron phosphate blade battery in 2020, 

which increases the energy density of the battery by 50% without changing the battery system, reduces manufacturing costs by 30%, 

and can withstand safety level tests such as collision, high temperature, and puncture. 

It will greatly expand the application field of lithium-ion batteries and has already supplied Tesla electric vehicles in bulk, 

achieving a technological revolution in lithium-ion batteries and leading the way into the era of lithium iron phosphate super batteries.

3 Advanced Battery Manufacturing and Characterization Technologies

(1) Artificial intelligence/machine learning assisted battery research and development

In the field of energy storage materials, especially battery materials, 

machine learning technology has been widely applied to predict and discover the properties of materials. 

In the past, researchers constantly tried different materials and processes, 

which were inefficient and difficult to meet the rapidly developing needs of high-tech industries. 

Artificial intelligence (AI) has powerful high-speed and massive data processing capabilities, 

and is the most promising technology to break through the research bottlenecks mentioned above, greatly promoting the development of battery material research, 

battery device design and manufacturing, material and device characterization, and other aspects. 

The research and application of batteries generate a large amount of data every day. 

Artificial intelligence and machine learning can assist researchers in solving the parameter and data challenges of lithium-ion batteries, 

greatly promoting the industrialization of large-scale and high-performance electrochemical energy devices.

(2) Artificial intelligence assisted lifespan and health status prediction technology

With the deepening of interdisciplinary research, 

the field of battery modeling is increasingly adopting various artificial intelligence methods to improve battery management efficiency, 

enhance the stability and reliability of battery operation. 

In order to ensure the efficient and safe operation of batteries and improve the service life of lithium-ion battery systems,

it is crucial to predict the remaining life of batteries and evaluate their state of health (SOH). 

By monitoring the status and parameters of the battery in real-time, artificial intelligence can predict the battery's lifespan and risk of failure, 

perform maintenance and replacement in advance, and ensure the reliability and safety of the system. 

At present, there are some problems with using neural networks to analyze battery State of Health (SOH). 

In practical applications, the operating conditions of batteries are very complex, and multiple methods need to be combined to obtain more accurate results. 

In the future, based on the basic theory of power systems in service environments and the theory of multi physics coupling failure, 

the synchronization of short-term and long-term performance with service physical entities can be achieved through multidimensional sensing information transmission and import. 

Collaborative diagnosis of multi-source information fusion can be carried out for states and faults, 

improving the intelligent management level and full life cycle operation reliability under service conditions.

4 、Other

(1) Fast charging design for batteries

From the overall development history of the battery side, the current power battery has basically solved the safety performance problem, 

and its range has generally exceeded 600 kilometers, and even exceeded 1000 kilometers, gradually resolving range anxiety. 

Therefore, it can break the anxiety of terminal mileage and energy replenishment, further shorten the charging time, 

and become an important dimension for improving the penetration rate of electrification.

 Fast charging has become a technology scenario for many enterprises to increase their layout. 

The high temperature of the positive and negative electrode ears during high rate charging and discharging is a major bottleneck in battery fast charging technology. 

The non-polar ear technology adopted by 4680 changes the current transmission mode between the current collector 

and the positive and negative electrodes from traditional line transmission to surface transmission, 

greatly improving the flow area and overcurrent capacity, reducing battery internal resistance and heat generation, 

and achieving safe fast charging.

(2) Extreme Environment Battery Design

The fields of energy storage grids, aviation components, intelligent equipment, 

and cold ground transportation equipment are constantly developing, showing a trend of diversified loads and complex tasks. 

On the one hand, the composition of equipment is becoming increasingly complex, 

which puts higher demands on the specific energy and power density of battery power systems; 

On the other hand, various equipment mainly operates in various extreme environments, 

and the power output characteristics of battery systems have always been the focus and bottleneck of equipment development. 

Exploring fundamental scientific issues such as thermodynamics, kinetics, and stability of batteries in extreme environments, 

discovering new principles, developing new materials, technologies, devices, and systems, has significant scientific significance and practical value. 

Recently, the team of researcher Fan Xiulin from Zhejiang University developed and validated a new set of extreme electrolyte design principles, 

breaking the traditional lithium-ion transport mode and opening up a new research path for electrolytes with special physicochemical properties. 

Based on this concept, the team has designed a new type of electrolyte that not only supports reversible charging 

and discharging of high energy density lithium-ion batteries in the ultra wide temperature range of -70~60 ℃, 

but also enables fast charging and discharging of high-energy density lithium-ion batteries within 10 minutes. 

This research achievement provides new ideas and possibilities for the development of lithium-ion batteries with high capacity, high stability, 

and wide temperature operating range.

5、 Conclusion and Prospect

Lithium ion batteries are still the most mainstream commercial battery technology, widely used in fields such as mobile phones, tablets, laptops, and electric vehicles. 

However, lithium batteries still face some challenges in terms of safety, energy density, cost, and resource sustainability. 

For example, lithium batteries may experience safety issues such as overheating and explosion under extreme conditions; 

There is still room for improvement in energy density to meet the demand for long range electric vehicles; 

The limited availability of lithium resources also restricts the large-scale application of lithium batteries. 

In the future, lithium battery technology will develop in the following directions. 

Improving Energy Density: Researching new electrode materials, electrolytes, 

and structural designs to enhance the energy density of lithium batteries, achieving longer range and higher power output. 

Enhance safety: Develop new electrolytes, 

separators, and battery management systems to improve the safety of lithium batteries and reduce the risk of overheating, combustion, or explosion. 

Reduce costs: Optimize production processes, improve manufacturing efficiency, reduce the production cost of lithium batteries, 

and promote their widespread application in the fields of electric vehicles and energy storage. 

Realizing resource sustainability: exploring new ways of lithium resource extraction, improving recycling rates, reducing dependence on limited resources, 

and achieving sustainable development of the lithium battery industry. 

Multi functional applications: Combining emerging technologies such as artificial intelligence and the Internet of Things, develop smart lithium batteries with intelligent monitoring, self-healing, 

and other functions to meet the needs of different fields.

At present, global competition in battery research and development is becoming increasingly fierce, and governments, social capital, 

and participating teams attach great importance to and strengthen innovation in advanced batteries. 

China should increase its deployment in the field of next-generation battery technology in its science and technology plan, 

and form a national strategic technological force in the emerging battery field to win the initiative of global competition in the future battery industry. 

It is necessary to establish a national advanced battery innovation center and an industry university research alliance, 

make full use of the R&D capabilities of national laboratories, State Key Laboratory, leading enterprises and R&D centers of start-ups, 

and jointly promote the original innovation of batteries and in-depth research on basic scientific issues.