“Clean energy + energy storage + intelligence” is the development direction of the energy Internet. The future development of clean energy and smart energy is inseparable from energy storage. 2017 is the first year of energy storage in China. The introduction of the “Guiding Opinions on Promoting Energy Storage Technology and Industrial Development” marks the arrival of the spring of energy storage. Although the climate in early spring is warm and cold, the energy storage industry has begun to sprout and bloom. Energy storage projects, especially energy storage battery projects, in the fields of power generation, power grid, user side, microgrid, communication energy storage, emergency power supply, etc., are springing up like mushrooms after a rain, and the spring of energy storage has come. Energy storage technologies include physical energy storage (pumped hydro energy storage, compressed air energy storage, flywheel energy storage, seawater energy storage, superconducting energy storage), chemical energy storage (hydrogen storage, carbon storage), electrochemical energy storage (battery energy storage) , supercapacitor energy storage) and heat and cold storage. Among various energy storage technologies, battery energy storage is the fastest growing and most concerned energy storage technology direction. By the end of 2017, a total of 1,210.3 MW of global battery energy storage projects had been put into operation, and the cumulative scale entered the GW era for the first time.
1. Application scenarios of energy storage batteries
(1) Grid-connected renewable energy
The intermittent and volatile nature of renewable energy generation, as well as the increasing penetration rate, pose severe challenges to the normal operation and dispatch of existing grid systems. In recent years, in order to utilize more renewable energy as much as possible and improve the reliability and efficiency of grid operation, various energy storage technology research and engineering demonstration projects have developed rapidly. The large-capacity battery energy storage technology is applied to wind power and photovoltaic power generation, which can smooth the power output fluctuation, reduce its impact on the power system, improve the power station’s ability to track the planned output, and provide backup energy for the construction and operation of renewable energy power stations.
(2) Power grid auxiliary services
Grid auxiliary services are divided into capacity-based and power-based services. Capacity-based services such as grid peak shaving, load following and black start, etc., the scale of energy storage needs to reach a certain volume, generally between 1 and 500 MW, and the discharge time is greater than 1 hour; Power-based services such as FM assist and voltage support require a large power or voltage output from the battery for a short period of time (on the order of minutes). In terms of improving the frequency regulation capability of the power grid, the energy storage battery technology can reduce the loss of traditional frequency regulation power supply caused by frequent switching; in terms of improving the peak regulation capacity of the power grid, the energy storage system can respond to dispatching in a timely and reliable manner according to the changes in power supply and load command, and change its output level according to the command.
(3) Power grid transmission and distribution
Energy storage battery systems can improve power distribution quality and reliability. When the distribution network fails, it can be used as a backup power supply to continuously supply power to users; in terms of improving power quality, it can be used as a system controllable power supply to manage the power quality of the distribution network, eliminate voltage sags, harmonics and other problems, while reducing the backbone Network expansion investment, saving expansion funds.
(4) Distributed and micro network
The microgrid system requires an energy storage device, and the energy storage device is required to be able to do the following: 1) Provide short-term uninterrupted power supply in the case of off-grid and distributed power supply cannot supply power; 2) Can meet the peak regulation of the microgrid 3) It can improve the power quality of the microgrid; 4) It can complete the black start of the microgrid system; 5) It can balance the output of intermittent and fluctuating power sources, and effectively control the electrical load and thermal load. The energy storage battery system has the characteristics of dynamic energy absorption and timely release. As a necessary energy buffer link of the microgrid, it can improve the power quality, stabilize the network operation, optimize the system configuration, and ensure the safe and stable operation of the microgrid.
(5) User side
User-side energy storage mainly includes industrial and commercial peak shaving and valley filling and demand-side response. Batteries combined with power electronics technology can provide users with reliable power supply and improve power quality; and use the difference between peak and valley electricity prices to save users expenses.
(6) Energy supply system of electric vehicle VEG mode
The development of the new energy vehicle industry must be coordinated with the energy storage industry. In order to meet the demand for safe and fast charging of electric vehicles in the future, it is necessary to establish a distributed energy station similar to a gas station. The energy station is equipped with a low-cost, long-life megawatt-level energy storage battery, which can be charged and stored from the power grid and used for electric vehicles. Cars are charged quickly; at the same time, the energy station can also interact with the grid for power peaking or frequency regulation.
2. Types of energy storage batteries
The complexity of energy storage application scenarios determines the diversified development direction of energy storage battery technology. Selecting the appropriate energy storage battery technology for application in specific scenarios will be the main theme of the energy storage market for a long time in the future. The research and development direction of new energy storage battery technology in the future should also follow this law, and amplify its advantages for specific scenarios to obtain the future. possibility of commercial application.
There are many characteristic parameters to characterize the performance of energy storage batteries, the most important of which are the power characteristics and capacity characteristics of the battery. Therefore, according to the different requirements of battery power-capacity ratio (W: Wh, C for short) in different energy storage application scenarios, energy storage batteries can be roughly divided into three types: capacity type (≤0.5C), energy type (≈1C) ) and power type (≥2C). The larger the ratio, the higher the power density of the battery, but the lower the capacity density and the higher the price per unit capacity.
For example, power peak regulation, off-grid photovoltaic energy storage or user-side peak-valley price difference energy storage generally requires the energy storage battery to be continuously charged or discharged for more than two hours, so it is suitable for the application of capacity batteries; for power frequency regulation or smoothing For energy storage scenarios with fluctuating renewable energy, the energy storage battery needs to be charged and discharged quickly in the time period from seconds to minutes, so it is more suitable for the application of power batteries; and in some application scenarios that need to undertake frequency regulation and peak regulation at the same time, Energy-based batteries are more suitable. Of course, power-based and capacity-based batteries can also be used together in this scenario.
Among the current types of energy storage batteries, flow batteries and lithium slurry batteries are typical capacity batteries, and lithium titanate batteries in lithium ion batteries are a typical type of power batteries. This is due to the nature of the above batteries. Attributes are determined and difficult to change. Other types of batteries can be adjusted to a certain extent by changing battery materials and processes to adapt to different energy storage application scenarios.
3. Technical connotation of energy storage battery
In the future, large-capacity batteries for power peak regulation energy storage and high-power batteries for power frequency regulation energy storage still need technological innovation breakthroughs. The content of energy storage battery technology mainly includes six aspects: material technology, structural technology, manufacturing technology, application technology, repair technology and recycling technology.
(1) Material technology
The core materials of the battery include positive electrode materials, negative electrode materials and electrolyte materials, and auxiliary materials also include separators, current collectors and battery shell materials. In the past three decades, the research and development of lithium-ion battery materials has mainly focused on improving the energy density, cycle life and safety performance of materials, and developing low-cost material preparation technologies; the research and development of flow battery materials has mainly focused on electrolytes and separators. Modification of materials. In 2006, in the field of lead-acid batteries, the selection and modification of carbon material additives in negative electrode lead paste began to develop long-life lead-carbon batteries for energy storage.
Throughout the research history of energy storage battery technology, although the progress of materials can bring about significant improvements in battery performance, the process of material innovation that can have practical effects is actually very slow. In particular, the performance of materials reported in laboratory papers is not equivalent to the performance of actual batteries, and there is often a considerable gap between the two. Therefore, although battery materials are critical, they are not the whole of battery technology research. At present, the establishment of technical engineering projects in the field of energy storage places too much emphasis on the research work of materials in the laboratory, ignoring the connection with practical application scenarios, resulting in a large disconnect between scientific research work and industrial development needs, which should be paid enough attention.
(2) Structural technology
Not all batteries can be called energy storage batteries. If the system power is above 1KW, they can be called energy storage batteries; if the system power is greater than or equal to 1MW, the batteries used in energy storage power stations are called power energy storage batteries.
Energy storage battery structure technology includes battery cell internal structure technology and external system structure technology. Different from batteries used in small consumer electronic products, the structure of energy storage batteries is more complex, and it has the requirements of series and parallel systems and the characteristics of high power and large capacity.
Existing energy storage and power lithium batteries are developed from micro-miniature lithium-ion batteries such as mobile phone batteries. Whether it is a cylindrical or a square battery, from the perspective of internal structure, all types of lithium batteries are internally bonded. The structure of the thin film electrode brings a fundamental structural problem to the design of the performance consistency of lithium batteries for energy storage. In addition, when the battery is scrapped and recycled, all the bonded electrodes can only be pulverized, and the internally broken aluminum foil, copper foil materials, Co, Li elements, etc. need to be recycled by metallurgical methods, resulting in high recycling costs and acid-base waste liquid pollution. deal with risks. Therefore, it is necessary for the structural design of lithium batteries for energy storage to learn from the structural ideas of large-scale batteries such as lead-acid batteries and flow batteries, so as to change from “petite and rich” that is prone to problems to safe and reliable “stupid and bulky”. It is suitable for energy storage application scenarios with high current and high power.
The research and development of large-scale energy storage batteries in the future also needs to consider the integrated design of the internal structure and external structure of the battery. For electric energy storage, application end customers are concerned about system cost, system efficiency, system life and system safety, but not about the energy density of single cells or the cycle life of single cells. Therefore, as a battery technology research and development end, it should actively consider the innovative integration of the internal structure of the cell and the external structure of the system, and reduce the cost and safety pressure faced by the external system through the subversive design of the internal structure. This will be an important direction for future research on energy storage battery structure technology.
(3) Manufacturing technology
The energy storage battery manufacturing technology is closely related to the battery structure design. The series-parallel characteristics of the energy storage battery system require that the batteries must have good consistency, so the intelligent management and control of the production process is particularly important. How to manufacture high-performance energy storage batteries with low-cost equipment and processes? This is a contradictory question, and it is also a key issue in the development of energy storage battery manufacturing technology.
The existing lithium-ion battery production process is a transition from the past tape manufacturing process to meet the precision requirements of the battery film-coated pole piece. In addition, the battery product models are varied and lack specifications, resulting in a low material utilization rate in the battery production process. , The product qualification rate is low, the equipment operation rate is low, and the manufacturing cost is high. Therefore, in the future, it is necessary to combine the subversive design of the battery structure to fundamentally reduce the complexity of the energy storage battery production process and the parameter requirements of the production equipment, and at the same time promote the integration of big data, Internet of Things technology, and energy storage battery production equipment and manufacturing processes. , through intelligent manufacturing upgrades, standardize manufacturing process standards, strictly control product quality, improve product final inspection efficiency, and reduce the manufacturing cost of energy storage batteries.
(4) Application technology
Energy storage battery application technology mainly refers to BMS, PCS and EMS. BMS (Battery Management System) is the link between the battery body and the application side. The main object is the secondary battery. The purpose is to improve the utilization rate of the battery and prevent the battery from being overcharged and overdischarged. PCS (battery energy storage system energy control device) is a system that is matched with the energy storage battery pack, connected between the battery pack and the power grid, and stores the grid energy into the battery pack or feeds the battery pack energy back to the power grid. EMS (Energy Management System) is the general term of modern power grid dispatch automation system, including: computer, operating system and EMS support system, data acquisition and monitoring, automatic power generation control and planning, network application analysis.
At present, many energy storage demonstration projects are implemented directly by battery production suppliers and power grid companies, and there is a lack of responsibility identification standards and application technical standards, which brings difficulties to later system operation and maintenance and possible accident identification. In the future, there should be an independent energy storage battery system application service provider centered on application technology development, responsible for the design and planning, lease operation and maintenance, and scrap recycling of energy storage systems, and cooperate with insurance companies to promise to be responsible for the service life and operation of the system. Safety.
(5) Repair technology
The repair technology of the energy storage battery includes the electrical repair technology of the battery system and the online regeneration technology. The former includes environmental corrosion repair, electrical insulation aging detection, electrical connection detection, temperature and pressure sensing maintenance and battery inspection technology, etc. The latter is a new technical direction for new energy storage lithium batteries. Because theoretically, in addition to the problem of lattice disorder in the active particles of the battery and the corrosion and detachment of the current collector, other interface problems of the energy storage lithium battery may be maintained and extended through online regeneration. When the battery is used for a period of time, the battery performance can be re-activated by in-situ repair of the SEI film on the surface of the positive and negative materials, replenishment and replacement of the electrolyte, etc., to extend the actual calendar service life of the energy storage lithium battery. For example, the slurry-thick electrode morphology of lithium slurry batteries gives them the possibility of in-line regeneration during their lifetime.
(6) Recycling technology
Any battery has an expiration date. At present, the total domestic use of small consumer batteries is hundreds of millions, and most of them are small in size. The use value of waste batteries is low. In addition, the use is scattered, and most of them are treated as domestic waste, which poses a potential pollution risk. Scrapped energy storage batteries cannot be discarded into the environment like small consumer batteries, and must be recycled and regenerated.
The recycling technologies of energy storage batteries include the replacement and processing technology of waste batteries, safe transportation technology, recycling and processing technology and resource reuse technology. At present, the recycling and regeneration technology of lead-acid batteries is relatively mature, but there is a risk of pollution in the non-standard recycling process. The recycling process and technology of lithium batteries are still immature, and it is necessary to combine material technology and structural technology to develop new energy storage battery technology that is convenient for recycling and regeneration, innovate and improve product design, and consider battery recycling and processing from the production side in advance. , in order to achieve the sustainable development of resources in the energy storage lithium battery industry, which has important strategic significance.
4. Development goals of energy storage battery technology
The spring of energy storage has come, but the booming summer of the industry is far from here. Various energy storage technologies have been put into commercial or demonstration applications, showing the advantages of energy storage in the application, but also gradually exposed some problems, especially the battery Energy storage technology still has a long way to go from the development goal of “low cost, long life, high safety, and easy recycling”, and needs innovation and breakthrough.
(1) Low cost
The cost of the energy storage battery in the narrow sense only includes the primary (purchase) cost, and the cost of the energy storage battery in the broad sense also includes the secondary (use) cost and the tertiary (recycling) cost.
Among them, the primary cost includes the material cost and production cost of the battery. In the case of limited space for material cost reduction, through the subversive design of battery structure technology, simplifying the battery production process and reducing manufacturing costs and labor costs will be an important cost reduction direction for new energy storage batteries.
Secondary costs are closely related to battery life. It is necessary to combine material technology and structural technology to develop new repair and regeneration technology, improve battery service life, and reduce the cost per kilowatt-hour of capacity batteries and the frequency cost of power batteries.
The third cost mainly refers to the recycling cost of the battery. At present, if the recycling and regeneration of energy storage batteries fully meet the requirements of environmental protection standards, the cost is still very high. It is necessary to have innovative recycling and regeneration ideas to reduce the tertiary cost of batteries.
The cost reduction of energy storage battery technology can be divided into the following four target stages. Current goals: Develop energy storage battery technologies and markets with non-peak shaving functions, such as frequency-regulated energy storage batteries and mobile energy storage batteries; short-term (5-10 years) goals: LCOE lower than the peak-to-valley electricity price difference; medium-term (10 -20 years) target: lower than the cost of thermal power peak shaving and dispatching; long-term (20-30 years) target: lower than the kWh cost of wind and solar power generation in the same period.
Battery energy storage assisted AGC frequency regulation will be developed before peak regulation energy storage. In the future, only when the application cost of energy storage batteries is lower than the cost of thermal power peak regulation, the energy storage battery system can be developed on a large scale as an important supplement and incorporated into the peak regulation and dispatch system of the power grid.
(2) long life
Generally speaking, for consumer small batteries (such as mobile phone batteries), the service life of 3 to 5 years is enough to meet the life requirements of electronic products, but it is still hoped that the standby time of the battery after a single charge can be longer, so for the battery energy density has a higher direct demand. However, for power storage batteries, a calendar service life of ten or even more than twenty years is basically required. Therefore, it is particularly important to improve the calendar service life of energy storage batteries.
The battery cycle life is the basis for the calendar life, but not the actual calendar life of the battery. Because from a thermodynamic point of view, the battery system is a highly non-equilibrium chemical system, and there are also irreversible chemical changes in bulk and interface during a long cycle of use, resulting in an increase in the internal resistance of the battery and a decrease in capacity. At present, there is still a lack of suitable accelerated aging test standards that can correspond to the actual calendar decay changes of batteries. In the future, in addition to establishing relevant test standards, it is also necessary to develop innovative online repair and regeneration technologies to improve the calendar service life of energy storage batteries and meet the requirements of actual energy storage conditions.
(3) High security
The safety of energy storage batteries is very important. Relatively speaking, water-based batteries such as flow batteries and lead-acid batteries are relatively safe and can meet the safety requirements of energy storage power stations. Hydrogen evolution explosion; the safety problems of organic lithium-ion batteries are more prominent, and they are generally at the level of safety and pass line, and technical breakthroughs are needed; solid-state batteries do not contain flammable electrolytes, so they have the highest safety. In the future After mass production, it may be first applied to some special scenarios with high safety requirements. Of course, for solid-state batteries to be applied to power energy storage on a large scale, there are still considerable difficulties to be overcome in terms of cost reduction and life extension. In addition, the recycling of solid-state batteries is also a big problem.
Safety prevention technology to avoid battery (internal or external) short circuit and emergency maintenance technology after battery short circuit are important directions for the development of energy storage battery safety technology. It is far from enough to protect the safety of energy storage lithium batteries only through external fire extinguishing devices. In the future, subversive battery structure technology and safety maintenance technology must be developed to completely solve the battery safety problem from the inside of the battery and ensure the safety of the energy storage battery. Safe operation of transport and energy storage plants.
(4) Easy to recycle
The recycling and utilization of resources will be the biggest challenge for the future large-scale application of energy storage batteries. There are three basic requirements for energy storage batteries to achieve the goal of easy recycling: 1. The battery recycling process meets safety and environmental protection standards; 2. Rare and precious metal elements can be recycled close to 100%; 3. The battery has a certain recovery residual value.
The current energy storage lithium battery system for demonstration applications basically does not take into account the recycling and processing links after the battery is scrapped in the future. What is more serious is that there is a widespread misconception in the battery industry that scrapped lithium batteries are rich in various valuable precious metals, so there is no need to worry about recycling.
The actual situation that the author of this article has learned is that there are serious conflicts and contradictions between the “value” and “environmental protection” of scrapped batteries. The material system selection and battery structure design of the existing energy storage lithium battery make it fully meet the environmental protection requirements. Valuable recycling work is very difficult. Therefore, it is necessary to carry out detailed pollution analysis and environmental protection assessment of the entire energy storage battery industry chain, and guide the environmental protection development direction of energy storage battery technology innovation, so as to promote the healthy and sustainable development of the industry.
“Renewable energy + energy storage” is an inevitable choice for the development of new energy, and the complexity of energy storage application scenarios determines the diversified development direction of energy storage battery technology. In the future, large-capacity batteries for power peak regulation energy storage and high-power batteries for power frequency regulation energy storage still need technological innovation breakthroughs. Energy storage battery includes six technical connotations: material technology, structural technology, manufacturing technology, application technology, repair technology and recycling technology. Among them, battery materials are the basis, but not all of the research on energy storage battery technology. It is suggested that in the future, basic exploration projects can focus on the research of new materials, while technical engineering projects should focus on breakthroughs in other non-material technologies. With the overall goal of long life, high safety, and easy recycling”, develop various capacity-type peak-valley energy storage batteries, power-type frequency-modulated energy storage batteries and energy-type composite energy storage batteries, and cooperate with other types of energy storage technologies to support the energy storage industry rapid development.
The article is excerpted from: “China New Energy”, Issue 24, 2018, author: Researcher Chen Yongchong, head of the Energy Storage Technology Research Group of the Institute of Electrical Engineering, Chinese Academy of Sciences.