EV Charging
E
lectric vehicles (EVs) have quickly evolved from a niche market to the forefront of the automotive industry. At the heart of this revolution is one key component – the battery. More specifically, lithium-ion batteries have become the power source for most of today’s electric vehicles. But how did we get here, and where are we going? Let’s take a closer look at some of the lithium-ion batteries in electric vehicles.
Understanding Lithium-Ion Batteries
Before we get into the nitty-gritty, let’s break down what lithium-ion batteries are and why they’re such a big deal in the EV world.
Lithium-ion batteries aren’t some mysterious tech hidden behind layers of complexity. At their core, they consist of four main parts: the anode, cathode, electrolyte, and separator. Imagine a ping-pong game—lithium ions are like the ball, shuttling back and forth between the anode and cathode as the battery charges and discharges. The electrolyte serves as the medium for this exchange, while the separator keeps the anode and cathode from short-circuiting, like a referee ensuring fair play.
Lithium-ion Battery Classification
Lithium-ion batteries are batteries that use lithium compounds such as lithium manganese oxide, lithium phosphate or lithium cobalt oxide as positive electrodes, carbon materials that can embed lithium ions as negative electrodes, and organic electrolytes. Currently, the energy storage devices used in pure electric vehicles are mainly lithium-ion batteries.
Appearance Classification
Lithium Manganate Battery
The battery with lithium manganese oxide material as the positive electrode has a nominal voltage of 3.7V and is widely used for its low cost and good safety. Lithium manganese oxide (LiMn2O4) has a spinel structure, with a theoretical capacity of 148mA*h/g, an actual capacity of 90~120mA*h/g, and an operating voltage range of 3~4V. The main advantages are abundant manganese resources, low price, high safety, and relatively easy preparation. The disadvantages are that the theoretical capacity is not high; the material will slowly dissolve in the electrolyte, that is, the compatibility with the electrolyte is not very good; during the deep charge and discharge process, the material is prone to lattice distortion, causing the battery capacity to decay rapidly, especially when used at higher temperatures.
Lithium Iron Phosphate Battery
Lithium-ion battery using lithium iron phosphate as positive electrode material. Lithium iron phosphate (LiFePO4) has an olivine crystal structure, and its theoretical capacity is 170mA*h/g. Its actual capacity is as high as 110mA*h/g without doping modification. By surface modification of lithium iron phosphate, its actual capacity can be as high as 165mA*h/g, which is very close to the theoretical capacity, and the working voltage is about 3.4V. Lithium iron phosphate has the characteristics of high stability, greater safety and reliability, more environmental protection and low price. Lithium iron phosphate positive electrode material is considered to be the most promising positive electrode material for power batteries. Its disadvantages are high resistivity and low utilization rate of electrode materials. At present, carbon composite lithium iron phosphate is widely used as positive electrode material. Carbon composite lithium iron phosphate positive electrode materials are divided into energy type and power type according to charging and discharging characteristics and usage requirements.
Cobalt Oxide Lithium Ion Battery
Lithium-ion batteries that use lithium cobalt oxide as the positive electrode material. Lithium cobalt oxide batteries have superior electrochemical properties, are easy to process, have stable performance, good consistency, high specific capacity, and outstanding comprehensive performance; however, they have poor safety and high cost.
Nickel-cobalt-manganese Lithium-ion Battery
A lithium-ion battery that uses nickel-cobalt-manganese ternary material as the positive electrode. Nickel-cobalt-manganese lithium-ion batteries have high energy density, high power density, long cycle life, easy processing, and good safety.
Lithium-ion Battery Structure
Positive electrode: The positive electrode material is composed of transition metal oxides containing lithium. In manganese oxide lithium ion batteries, lithium manganese oxide is the main raw material, in iron phosphate lithium ion batteries, lithium iron phosphate is the main raw material, in nickel cobalt lithium ion batteries, lithium cobalt is the main material, and in nickel cobalt manganese lithium ion batteries, nickel cobalt manganese lithium is the main material. Conductive agent and resin binder are added to the positive electrode active material, and coated on the aluminum substrate, distributed in a thin layer.
Negative electrode: The negative electrode active material is made of a mixture of carbon material and binder, which is then blended with an organic solvent to form a paste, and coated on a copper base in a star-thin layer.
Diaphragm: The function of the diaphragm is to close or block the channel. Generally, a microporous membrane made of polyethylene or polypropylene is used. The so-called closing or blocking function means that when the battery temperature rises abnormally, the pores that serve as ion channels are blocked or blocked, so that the battery stops charging and discharging reactions. The diaphragm can effectively prevent the battery from generating abnormal heating due to excessive current caused by external short circuits. If this phenomenon occurs once, the battery cannot be used normally.
Electrolyte: The electrolyte is an organic electrolyte with a mixed solvent as the main body. In order to dissolve the lithium salt of the main electrolyte component, a solvent with high dielectric constant and good compatibility with lithium ions, that is, a low-viscosity organic solution that does not hinder the movement of ions is preferred. Moreover, within the operating temperature range of the lithium-ion battery, it must be in a liquid state with a low freezing point and a high boiling point. The electrolyte has chemical stability for the active substance and must be well adapted to the violent redox reaction that occurs during the charge and discharge reaction. Since it is difficult to meet the above harsh conditions using a single solvent, the electrolyte is generally used by mixing several solvents of different properties.
Safety valve: In order to ensure the safety of lithium-ion batteries, external circuits are generally controlled or a safety device is installed inside the battery to cut off abnormal current. Even so, during use, there may be other reasons that cause abnormal increase in the internal pressure of the battery. In this case, the safety valve releases gas to prevent the battery from rupturing. The safety valve is actually a one-time non-repairable rupture membrane. Once it enters the working state, it protects the battery and stops it from working. Therefore, it is the last means of protection for the battery.
Working Principle of Lithium-ion Battery
The positive electrode material of lithium-ion batteries must have a position and diffusion path that can accept lithium ions. Currently, the positive electrode materials with better application performance are transition metal oxides and lithium compounds with layered structures with high insertion potentials, such as lithium compounds LiCoO2, LiNiO2 or spinel structure LiMn2O4. The lithium insertion potential of these positive electrode materials can reach above 4V; the negative electrode material generally uses lithium-carbon intercalation compound LixC6; the electrolyte generally uses an organic solution dissolved with lithium salts LiPF6 and LiAsF6.
As shown in the figure below, during charging, lithium ions are deintercalated at the positive electrode and enter the negative electrode through the electrolyte. At the same time, due to the effect of the diaphragm, electrons can only flow from the positive electrode to the negative electrode through the external circuit, forming a charging current and maintaining the charge balance between the positive and negative electrodes. Similarly, during discharge, lithium ions are deintercalated at the negative electrode and flow to the positive electrode, and electrons form a discharge current in the external circuit.
The battery reaction process does not consume electrolyte nor produce gas, only lithium ions move between the positive and negative electrodes, so the structure of lithium-ion batteries can be made completely closed. In addition, under normal conditions, there are no other side reactions during the battery charging and discharging process, so the charging efficiency of lithium-ion batteries is very high, even reaching 100%.
Requirements for Lithium-ion Batteries
The requirements for lithium-ion batteries are divided into requirements for single cells, battery modules and battery assemblies. The requirements for lithium-ion single cells are the same as those for nickel-metal hydride single cells. The requirements for lithium-ion battery modules are the same as those for nickel-metal hydride battery modules, except for the low-temperature discharge capacity, charge retention and capacity recovery capabilities.
Low temperature discharge capacity: When the lithium-ion battery module is tested according to the prescribed method, its discharge capacity should not be less than 70% of the initial capacity.
Charge retention: When the lithium-ion battery module is tested according to the prescribed method, its room temperature and high temperature charge retention rate should not be less than 85% of the initial capacity.
Capacity recovery: When the lithium-ion battery module is tested according to the prescribed method, the capacity recovery should be no less than 90% of the initial capacity.
A lithium-ion battery assembly refers to a power system that is composed of one or more lithium-ion battery modules, circuit equipment (protection circuit, lithium-ion battery management system, circuit and communication interface), etc., and is used to provide electrical energy to electrical devices. The main technical requirements for lithium-ion battery assemblies are as follows.
Interfaces and protocols: The interfaces and protocols of the battery management system that constitutes the lithium-ion battery assembly include circuit interfaces and interface protocols, communication interfaces and communication protocols. The circuit interfaces and interface protocols include charging control guidance interfaces and interface protocols, single battery voltage monitoring circuit interfaces and interface protocols, charge and discharge control circuit interfaces and interface protocols, and I/O charge and discharge interface circuits and interface protocols; the communication interfaces and communication protocols include internal communication interfaces and communication protocols, charge and discharge communication interfaces and communication protocols, and user communication interfaces and communication protocols.
Positive and negative output connections: The positive and negative connections of the lithium-ion battery modules that make up the lithium-ion battery assembly can be bolted or pluggable. There should be clear polarity markings at the positive and negative connections. The positive pole uses a red mark and red cable, and the negative pole uses a black mark and black cable.
Power consumption: specifically refers to the peak power consumed by the battery management system circuit that makes up the lithium-ion battery assembly, which should comply with the requirements of the product technical documents provided by the manufacturer.
Consistency of lithium-ion batteries: Consistency refers to the consistency characteristics of the performance of single batteries that make up lithium-ion battery modules and assemblies. These performances mainly include actual electric energy, impedance, electrical characteristics of electrodes, electrical connections, temperature characteristics differences, decay rate and other complex factors. The consistency characteristics of batteries that make up lithium-ion battery modules and assemblies should be tested under specified load conditions and charge states. The consistency characteristics of lithium-ion batteries are divided into charging state consistency characteristics and discharging state consistency characteristics. The consistency of lithium-ion batteries is divided into 5 levels, and those exceeding level 5 are unqualified products.
Service life: Service life is divided into standard cycle service life and operating cycle service life. The standard cycle service life of lithium iron phosphate battery is greater than or equal to 1200 times: the standard cycle service life of lithium manganese oxide battery should be greater than or equal to 800 times. The operating cycle service life of lithium-ion battery assembly for electric vehicles can be expressed in terms of mileage.
Rated power: When lithium-ion battery modules with the same nominal voltage are used to form a lithium-ion battery assembly, the rated power of the battery assembly is equal to the product of the power of the battery module with the smallest power in the power lithium battery assembly and the number of modules. When battery modules with different nominal voltages are used to form a battery assembly, the rated power of the battery assembly is equal to the product of the rated power of the battery module divided by the minimum nominal voltage of the battery module and the nominal voltage of the battery assembly.
Conclusion
Lithium-ion batteries have come a long way since their early days, and they’ve been instrumental in driving the growth of the electric vehicle market. From their basic structure to their current state and future prospects, it’s clear that this technology is here to stay—at least for the foreseeable future. However, as with any technology, there are challenges that need to be addressed, from supply chain issues to environmental concerns. As the industry continues to evolve, it’s crucial that we keep pushing the boundaries of what lithium-ion batteries can do, while also finding ways to make them more sustainable and accessible.
The road ahead for lithium-ion batteries in electric vehicles is full of promise, but it will require continued innovation and collaboration across the industry. Whether it’s through next-generation batteries, improved recycling methods, or entirely new technologies, the future of electric vehicles—and the planet—depends on our ability to rise to these challenges.
Derek Ke
Hi, I’m Derek Ke, founder of Moreday.com, an expert in solar-protected electrical products and electric vehicle charging.
Over the past 15 years, we have helped nearly 500 customers (such as farms, residential, industrial, and commercial) in 60 countries solve new energy and green power problems. We aim to share more knowledge about solar power generation and new energy with everyone so that green electricity can enter thousands of households.
