The main bottleneck of battery technology in the field of aviation power is that its energy density is much lower than traditional aviation fuels.Due to insufficient battery energy density,current pure electric aircraft are mainly suitable for short distance flights,and their range is greatly limited.In order to overcome this limitation and achieve higher energy density,researchers are actively developing next-generation technologies using new battery materials and chemical compositions.Meanwhile,hydrogen fuel cell systems have also attracted attention from the industry due to their high energy density and zero emissions advantages.
As a core component in the development of modern electric aviation,the performance of aviation power batteries directly determines the power output,endurance,and operational efficiency of aircraft.In the aviation application scenario,battery power systems face strict energy requirements:on the one hand,they need to meet the instantaneous power requirements during high-speed cruising of the aircraft;On the other hand,it is also necessary to ensure continuous energy supply for long endurance missions.These special operating conditions pose technical challenges to aviation power batteries that far exceed those of ground transportation vehicles.Improving energy density can not only significantly enhance the payload capacity and range of aircraft,but also promote the commercialization process of green aviation technology.Therefore,exploring innovative paths for high-energy density aviation power batteries is of great strategic significance for achieving low-carbon transformation in the aviation transportation industry.
Overview of Batteries and Their Energy Density
Batteries convert chemical energy into electrical energy through electrochemical reactions,and their basic structure includes an anode,cathode,electrolyte,and separator.During discharge,the anode undergoes oxidation reaction and releases electrons,which flow through the external circuit to the cathode to generate electrical energy;At the same time,the cathode undergoes a reduction reaction and receives electrons.The electrolyte plays a role in ion conduction inside the battery,while the separator is used to isolate the anode and cathode to avoid short circuits,while allowing ions to pass freely.In the aviation power system,the battery can serve as the power source for the electric motor,which directly drives the propeller to rotate.
The energy density of a battery mainly involves two key indicators:mass energy density and volume energy density.High quality energy density can make aircraft lighter and reduce the energy consumption required to complete specific flight tasks;High volumetric energy density can reduce the space required for energy storage in aircraft,optimize aircraft design,and increase payload.Although both mass energy density and volumetric energy density are important considerations in aircraft design,the impact of mass energy density on aircraft performance is more significant.As the range increases,the total energy required for the aircraft to carry not only increases in absolute value,but also its proportion in the overall mass of the aircraft increases accordingly.Taking traditional aircraft as an example,fuel accounts for 15%of takeoff mass during short haul flights,while it can reach up to 40%during long haul flights.Therefore,mass energy density is the key factor determining the range of an aircraft.In contrast,the impact of volumetric energy density is more complex,involving not only how to effectively utilize limited space to store energy,but also the optimization of the internal layout and overall design of the aircraft.The impact is more reflected at the design level rather than directly limiting the aircraft's range.
Challenges in the application of aviation power battery technology
In the field of aviation power,there is a significant gap in energy density between batteries and traditional aviation fuels.From specific data,the mass energy density of traditional aviation fuel is about 50 times that of current lithium-ion batteries(up to 14000 W·h/kg),while the volumetric energy density is 14 times that of lithium-ion batteries(up to 9800 W·h/L).This significant difference greatly restricts the widespread application of current battery technology in the aviation industry.Although battery technology has shown some applicability in electric vertical takeoff and landing(eVTOL)and short to medium distance flights,its relatively low energy density still limits its practicality in long-distance travel compared to alternative fuels.
As the quality of aircraft increases,the requirements for the quality and energy density of battery packs also increase.According to the Faraday Institute in the UK,a small regional electric aircraft with a passenger capacity of 30 and a range of 648km will need to achieve a mass energy density of approximately 600W·h/kg in the future;A narrow body(single channel)electric aircraft with a capacity of 150 passengers and a range of 926km requires a mass energy density of 820W·h/kg;The wide body(dual channel)electric aircraft with a passenger capacity of 300 and a range of 1852km requires a battery mass energy density of up to 1280W·h/kg.According to a study published in the journal Nature,in order to meet the power requirements of an aircraft carrying 150-180 passengers,the energy density of its battery system needs to reach a level of 1800-2500 W·h/kg.
The International Commission on Clean Transport(ICCT)has currently put forward clear requirements:by 2050,regional electric aircraft carrying 30-75 passengers with a range of approximately 926km need to achieve a mass energy density of 500W·h/kg and a volumetric energy density of 1100W·h/L to meet critical commercial needs.Table 1 presents the specific requirements of ICCT for the mass energy density and volumetric energy density of regional electric aircraft battery packs under different time frames.
However,there is still some debate and disagreement among experts regarding whether the energy density proposed by ICCT can fully meet the practical needs of the aviation industry.But with the improvement of battery performance,coupled with the application of next-generation chemicals,reduced aircraft weight,and improved aerodynamic efficiency,the prospects of electric aircraft are still worth looking forward to.From the relationship between aircraft range,battery quality,and energy density in Figure 1,it can be seen that when an aircraft is equipped with a battery system with a total mass of 5000kg and a mass energy density of 500W·h/kg,its range is expected to exceed 600km,which will further expand the application scope of electric aircraft and stimulate broader market demand.
There are two ways to improve the energy density of aviation power batteries:one is to develop high-energy density batteries to enhance battery energy storage efficiency;The second is to optimize the structural design of the aircraft,using lightweight materials(such as carbon fiber composite materials)and advanced manufacturing technology to reduce the overall weight of the aircraft,thereby improving the range under the same battery capacity,or increasing battery capacity while maintaining the target range.Although reducing weight is crucial for all aircraft,the performance and range of electric aircraft mainly depend on the overall energy density of the battery.In order to further increase the range of electric aircraft,the industry must actively explore and adopt various battery chemistry technologies.
Analysis of the Development of Aviation Power Battery Technology
The energy density of batteries plays a crucial role in the field of electric aviation.Due to the low energy density of current energy storage batteries,existing battery powered aircraft are mainly suitable for short distance flights.Consumer grade drones commonly use lithium polymer and nickel cadmium batteries as power sources,while short distance electric aircraft such as eVTOL mainly use lithium-ion batteries.However,with the development of emerging technologies such as lithium sulfur batteries and lithium air batteries,the energy density of batteries is expected to experience a qualitative leap.At the same time,the research and development of hydrogen fuel cells is steadily advancing,which is expected to help achieve high energy density and zero carbon emissions,bringing a disruptive change to the development of aerospace technology.
Traditional lithium polymer and nickel cadmium battery technology
Lithium polymer(LiPo)batteries are currently the preferred power source in the field of unmanned aerial vehicles.Its core feature is the use of solid polymer electrolyte modules(such as plastic or gel),so that the battery has a strong power output,lighter weight and lower self discharge rate.The low self discharge rate ensures that the battery can maintain sufficient power for a long time when not in use,which is particularly important for drones that are not frequently used.In addition,LiPo batteries also have flexible morphological characteristics and can be made into various shapes and sizes according to different designs and configurations of drones.The energy density of LiPo batteries typically ranges from 140 to 200 W·h/kg and 250 to 350 W·h/L.
Nickel cadmium(NiCd)batteries are also a common type of battery in the field of unmanned aerial vehicles,using nickel oxide hydroxyl and metal cadmium as electrode materials.Although not as popular as LiPo batteries,NiCd batteries still have some significant advantages,such as high discharge rate and strong power output,as well as normal operation under relatively harsh temperature conditions.However,NiCd batteries also have some obvious drawbacks,including relatively low energy density,environmental issues that may arise from the use of cadmium,and the so-called'memory effect',where the battery gradually reduces its available capacity during repeated charging.Figure 2 compares the volumetric energy density and mass energy density of several common types of drone batteries.
Current commercial lithium-ion battery technology
Lithium ion batteries have been widely used in the field of electric aviation due to their high energy density,long cycle life,and lightweight characteristics.At present,the energy density of commercial lithium-ion batteries has reached between 250-300W·h/kg,and the volumetric energy density has reached around 700W·h/L.They are mostly used in small unmanned aerial vehicles,eVTOL aircraft,and electric planes.
Drones using lithium-ion batteries are commonly used for agricultural monitoring,geographic mapping,film and television shooting,etc.Currently,the typical representative is the DJI Phantom series,equipped with 5870mA·h lithium batteries,which can support approximately 28 minutes of flight time and a range of 5-15km;EVTOL aircraft is also one of the application areas of lithium-ion batteries.The five eVTOL aircraft developed by Joby company use custom designed high-voltage lithium-ion battery packs with a total energy density of 288W·h/kg,which can achieve a payload range of over 240km;In addition,some research institutions and technology companies are exploring the possibility of larger electric aircraft.The Alice electric aircraft developed by Eviation,an Israeli company,is a groundbreaking example(see Figure 3).The aircraft uses an 820 kW·h lithium-ion battery system with a mass of about 3700 kg,which can provide 1 hour of flight time for the aircraft after 30 minutes of charging.It is planned to start commercial operation in 2027 and is expected to achieve a range of about 800 km.
According to the Faraday Research Institute in the UK,the maximum mass energy density of lithium-ion battery packaging will reach 370W·h/kg by 2035,and is expected to increase to 500W·h/kg by 2050.Although lithium-ion batteries have been successfully applied to the power systems of active pure electric aircraft,they still face many challenges.Lithium ion battery technology is limited by its inherent technological bottlenecks,including limited charging cycles,temperature sensitivity,and relatively low energy density limits,which collectively constrain the endurance performance of aircraft.What is even more worrying is that lithium-ion batteries have a small probability of failure,which may lead to thermal runaway and potentially cause fires or explosions,posing a potential threat to aviation safety.In order to meet aviation performance requirements and provide higher levels of safety assurance,it is necessary to develop new battery units.
Next generation chemical battery technology
In the field of lithium batteries,the next generation of lithium metal and silicon anode materials have become a research hotspot due to their high energy storage potential,and are expected to be commercially applied in the mid to late 21st century,bringing disruptive energy storage solutions to the market.At the same time,solid-state lithium-ion batteries have also shown great potential for development.Their oxide and sulfide based solid electrolytes can not only improve the safety of batteries,but also have the potential to further enhance energy density and cycle life.Table 2 shows the unit energy density and performance indicators based on existing advanced battery technologies.Lithium sulfur batteries and lithium air batteries are two revolutionary technologies with great potential,and their energy density is expected to break through the existing boundaries in the field of chemical batteries.However,currently these two technologies are still in the early stages of basic research.Once it goes commercial,the electric aviation industry may usher in a huge transformation.
Lithium sulfur batteries have become a highly anticipated new battery technology due to their high energy density,cost-effectiveness,and excellent safety.This technology was initially applied in fields such as satellites,drones,and military vehicles,and has now shown broad application prospects in the aviation industry,especially in short-range electric aircraft and eVTOL aircraft.Compared to mainstream lithium-ion batteries,lithium sulfur batteries can provide more than twice the energy density.Currently,their energy density has reached 500W·h/kg and is expected to further increase to 700W·h/kg.This improvement is mainly attributed to the application of sulfur cathodes,with a theoretical energy density of up to 2700W·h/kg.However,lithium sulfur technology also faces some significant drawbacks that cannot be ignored.The low electronic conductivity of sulfur cathodes limits the power density of lithium sulfur batteries,and the shuttle effect of polysulfides can cause internal corrosion,resulting in a much shorter cycle life of lithium sulfur batteries compared to traditional lithium-ion batteries.In addition,although lithium sulfur batteries theoretically have potential safety advantages,this advantage has not been fully validated in commercial systems.These challenges have become key factors restricting the large-scale application of lithium sulfur battery technology.In order to overcome these challenges,numerous battery research and development institutions around the world are actively conducting research in order to find effective solutions to overcome the limitations of lithium sulfur batteries.The Lithium Sulfur Technology Accelerator(LiSTAR)project at Faraday Research Institute in the UK has successfully achieved a mass energy density of 441 W·h/kg and a volume energy density of 735 W·h/L by using pre lithiated two-dimensional molybdenum disulfide as the sulfur host material in lithium sulfur batteries.After 200 cycles,the battery capacity can still maintain 85%;American battery startup Lyten is also developing a lithium sulfur battery suitable for automobiles and aircraft,innovatively using a metal lithium anode and a three-dimensional graphene sulfur composite cathode.Lyten expects that by 2027,this battery will be 60%lighter than lithium-ion batteries,with a mass energy density of up to 600W·h/kg and a lifespan of over 800 cycles.If solid electrolytes are further used,the mass energy density of the battery may exceed 1000W·h/kg.
Lithium air battery is another battery chemistry technology with broad application prospects in the field of electric aviation,known as the"ultimate battery".The battery uses lithium metal as the negative electrode and conductive carbon material as the positive electrode.During the discharge process,lithium ions released from the negative electrode will undergo electrochemical reactions with oxygen in the surrounding air.This technology is expected to provide 5 times higher energy density than current lithium-ion technology.From theoretical calculations,the energy density of this battery is currently the highest among all known lithium battery systems.Even when operating at only 10%of its maximum theoretical mass energy density(i.e.1000W·h/kg),the range of lithium air batteries can reach 1500km,which is sufficient to meet the needs of all short haul flights.The Argonne National Laboratory in the United States has greatly improved the durability of lithium air batteries by increasing their capacity,and has achieved 1000 charge and discharge cycles,meeting practical standards.The mass energy density of the coin sized test battery during operation is about 685W·h/kg,while it can actually reach 1200W·h/kg.However,this technology also faces some challenges,such as limited power density and poor energy efficiency during cycling.In addition,although using pure oxygen can avoid the influence of impurities in the air,the ultimate goal of lithium air batteries is still to directly use air.These problems are not insurmountable,but sustained research investment is needed to achieve breakthroughs.In order to further promote the commercialization of lithium air batteries,Osaka University in Japan,with the support of the Japan Science Agency(JST),will conduct international joint research with the United States,Germany,and the United Kingdom starting from February 2024,striving to commercialize lithium air batteries in the first half of the 2030s.
Zero carbon hydrogen fuel cell technology
With the increasing global demand for decarbonization in the aviation industry,the application of hydrogen fuel cell technology in the field of electric aviation is gradually receiving attention.A hydrogen fuel cell is a power generation device that uses hydrogen gas as fuel and directly converts the chemical energy in the fuel into electrical energy through electrochemical reactions.It has the advantages of high efficiency,zero emissions(zero emissions of nitrogen oxides and particulate matter),and no noise.
The mass energy density range of hydrogen fuel cells is between 1000 and 3000 W·h/kg.This means that these types of batteries can store more energy while ensuring lighter weight.At present,HyPoint's hydrogen fuel cell system has achieved a mass energy density of 1500W·h/kg and a specific power of 2kW/kg.Compared with turbine powered rotary wing aircraft,eVTOL aircraft using this hydrogen fuel cell system can reduce direct operating costs by up to 50%.Airbus'ZEROE project conducted ground tests on an iron pod in 2024,which includes a hydrogen fuel cell system(see Figure 4),an electric motor required for rotating propellers,and control and cooling devices.The power of hydrogen fuel cells reaches 1.2MW,and their energy density has not been disclosed yet,but based on existing material estimates,it may approach or reach 1500W·h/kg.
The core advantage of hydrogen fuel cell technology lies in its extremely high mass energy density,which makes it a key choice for the transformation of aviation power.At a unit mass,hydrogen fuel cell systems can provide much more energy than lithium battery systems,which is the most competitive technological foundation for hydrogen powered aircraft.However,the disadvantage of hydrogen fuel in terms of volumetric energy density cannot be ignored.Compared with traditional aviation kerosene,storing the same amount of energy requires a larger fuel storage space,which poses a significant challenge to aircraft structural design.
From the perspective of energy conversion efficiency,although current hydrogen fuel cell systems experience certain losses in the energy conversion process,resulting in relatively low overall efficiency,their excellent mass energy density characteristics still make them the optimal solution to overcome the range limitations of existing electric aircraft.Based on the current technological development path prediction,through continuous optimization of stack efficiency and energy management systems,the practical range of hydrogen powered aircraft is expected to exceed 2000km by 2030,far exceeding the limits of other battery systems.With the breakthrough of next-generation efficient cooling technology,this number may further increase to 4000km by 2035.At that time,hydrogen fuel cells will rise strongly and are expected to replace 30%to 50%of fossil fuel consumption.
To achieve this goal,breakthroughs in the future development of aviation hydrogen fuel cells will mainly focus on three dimensions:firstly,innovation in key materials,including optimized design of composite bipolar plates,new end plates,and membrane electrode components;Secondly,there will be improvements at the system level,with a focus on increasing the loading capacity of platinum catalysts to significantly optimize heat dissipation,gas supply,fuel regulation,and water management systems;Finally,there is an innovation in manufacturing processes,which achieves a comprehensive improvement in the performance of fuel cell systems by introducing intelligent monitoring systems and sustainable materials.These technological advancements will collectively drive the commercialization of hydrogen fuel cells in the aviation industry.
Conclusion
Electric aircraft,as an emerging technology in the aviation field,is gradually showing great development potential and broad market prospects.Although battery technology still cannot compete with fossil fuels in terms of energy density,it has demonstrated extraordinary potential in the short haul and regional electric aviation market.However,to meet the stringent requirements of commercial aviation,revolutionary breakthroughs are still needed in areas such as energy density,materials science,and system integration,rather than being limited to gradual technological improvements.This requires intensified cooperation between industry,academia,and research institutions to jointly promote technological innovation and achievement transformation to address technological bottlenecks and market challenges,and to promote the continuous development and improvement of battery technology and electric aircraft.
