The monks can't solve their problems. Chow
Under multiple environmental and policy impacts, new energy vehicles, especially electric cars, are being sold at high and fast speeds。
But behind rapid development, comments about electric vehicles have always been accompanied by a mixed voice of approval, such as energy-saving but too costly to purchase, environmentally friendly but not sustainable, and these contradictions are determined by the fact that the core parts of electric vehicles are “three power” — batteries, electric power, electrical control。
And in the “triple power”, the battery plays the most important role, as it is called, the “wieldy woman is no rice cook”, even if the power control, the electric power technology is advanced, the battery function as the power source is not working, and the whole vehicle's performance will be significantly compromised. This paper briefly explores the main underlying parameters of batteries。
A brief history of batteries
The earliest development of batteries dates back to 1800, when italian scientists developed volta, the world's first battery capable of practical application. Lead-acid batteries were invented by french scientist plante in 1859, the first chargeable battery in the world。
Since then, scientific and technological levels have been increasing, driving the generation of batteries, the emergence of alkaline zinc-manganese dry batteries in the 1950s, the success of fuel cell development in the 1960s, the success of lithium batteries in the 1970s, the emergence of hydrogen-nickel batteries in the 1980s and the emergence of lithium ion batteries in the 1990s, and the development of “well blow-out” battery technology。
The lithium ion batteries (hereinafter referred to as lithium batteries) used in the electric vehicles discussed in this paper are the source of this development. The development of lithium batteries has also gone through a period of “cattle” mapping, with a general development of three stages:
In stage 1, because the negative polar material is lithium metal and its alloys and is non-chargeable, lithium batteries are more accurately expressed as lithium metal single batteries
In stage 2, the negative polar material remains lithium metal and its alloys, but the positive polar material is replaced by a transoxidated compound such as mos2, allowing the lithium ion to be recharged in the positive-negative back-to-back movement of the battery, so that the lithium cell at that stage is essentially a lithium metal secondary battery
In stage 3, negative polar materials are graphite, coke, etc., conductive electrodes, and positive polar materials are lithium-containing compounds, such as lithium-layed intermediate metal oxides, lithium-layed metal sulphides, lithium salt compounds. The lithium batteries at this stage are essentially what we now call lithium ion batteries。
Lithium cell structure
The main structures of lithium batteries are positive polar, negative polar, electrolyte, diaphragm and outer crust。
(1) positive
Features: stabilization of electrochemical energy, non-decomposition structure, higher and better ratio capacity。
Classification (commercial): lithium phosphate (lfp), lithium cobaltate (lco), lithium manganeseate (lmo)
Triple materials: lithium nickel manganese cobalt-acid (ncm), lithium nickel manganese aluminiumate (nca)
Positive materials account for 30 to 40 per cent of the cost of lithium batteries and directly affect battery performance, even though they are now classified on the market according to positive materials, which can be seen as important to lithium batteries。
(2) negative
Characteristics: high-to-capacity, more reversible, lower than lithium electrodes。
Classification (commercial): currently dominated by carbon materials graphite (limited capacity)
Future trends in silicon-carbon composites (larger than capacity, 2-3 times the average graphite)
(3) electrolyte
Characteristics: high ion conductivity, wide electrochemical stabilization window, no reaction to electrodes, safety, non-toxic, non-pollution。
Composition: solvent (30%): ethylene carbonate, dimethyl carbonate, etc
Solvents (50%): lithium salt (lipf6, libf4, etc.) additives (10%), others (10%)。
Lithium cell parameters
(i) battery capacity c: the amount of charge released by the battery, under certain conditions, in mah or ah。
The battery capacity according to the conditions of use can be divided into:
Theory capacity: assuming that active substances are fully used, batteries can release electricity。
Scaled capacity: the amount of electricity released by fully charged batteries under laboratory conditions。
Actual capacity: physical use environment (but battery conditions are met), discharges from full battery, less than rated capacity
(ii) battery energy: measures how much energy is stored in batteries, in wh。
Formula: energy = rated voltage x working current x working hours = uit = rated voltage x battery capacity
E. G., millet cell phone batteries, cell energy 7. 3 wh=3. 7v x 1960mah/1000
Battery energy is an important indicator of cell-driven equipment. If battery capacity is understood to be the volume of water stored in the reservoir, then battery energy can be understood to be the ability of the reservoir to perform at a certain altitude。
Under the same voltage, the larger the battery capacity, the greater the battery energy, for example, the cell phone is replaced with a larger capacity in life, with the aim of increasing the battery energy, which can be increased if the working voltage remains unchanged. So does this work in electric cars
The answer is not necessarily, because the continuation of the electric car is different from the way in which the mobile phone continues to consume electricity to function, the weight of the battery increases as the battery capacity increases and the weight of the vehicle increases, so there are two variables, which at this point involve another critical energy parameter for the battery — energy density。
(iii) energy density: is the energy released by a unit volume or unit mass, expressed as a volume energy density (wh/l) or a mass energy density (wh/kg), which is a direct influence on the viability of electric vehicles。
The energy density is divided mainly into single-body energy density and system energy intensity. Single energy density is the minimum unit energy density, e. G. A section of lithium batteries weighing 325g, rated voltage of 3. 7v, capacity of 10ah, and energy density of 113wh/kg. System energy density is the energy density of a car's battery or plate。
Batteries or panels are mainly sealed in a number of single-cell cells, battery frames, pallets and other electrons, so that the energy density of the system is influenced by single-body energy density and containment technology and is less than a single energy density. The following is a chart of future performance plans for lithium batteries in china。
Energy density is also one of the core indicators for new energy vehicle subsidies, with the system energy density threshold in the criteria for new energy vehicle subsidies for previous years being as follows。
From the model configuration issued by the ministry of industry and communications on a monthly basis, it can be seen that the system energy density threshold for the calendar year reflects the current market for battery applications in a more realistic way — there is still a gap between national planning requirements and the long way to go for electric vehicles to develop。
(iv) voltage
There are three types of battery voltage:
Open circuit voltage: when the battery is not connected to an external circuit or load, the opening circuit voltage is proportional to the remaining energy of the battery and is the main basis for the principle of showing the remaining power of the electric vehicle。
2. Working voltage: the power differential between positive and negative poles, or load voltage, in a working state. Working voltage < open circuit voltage > , since internal barriers must be overcome when batteries are discharged。
3. Discharge cut-off voltage: voltage reached when the battery is fully charged. Continued discharge is excessive discharge, with impairment of battery life and performance。
Lithium batteries are the highest of single battery voltage values, which is one of the main reasons why lithium batteries are powered batteries。
(v) charge multiplication rate (c)
Is the current size of the charge and the value equals the number of times the rated capacity. Charging factor = chargeable current plating capacity, expressed as "c"。
(vi) other parameters
1. Cycle life: the number of cycles that batteries experience when they are recharged is described as a cycle or cycle, and when the battery is recharged repeatedly, the capacity is gradually reduced, and when the battery capacity is reduced to 80 per cent under certain discharge conditions, the number of cycles that batteries experience is the circulation life。
2. Self-release: batteries are stored in a manner that reduces their capacity as a proportion of the battery capacity, known as the self-release rate. For '%/month '. The lower the discharge rate, the better the storage performance。
3. Intrusion: means the resistance of the battery to current flow inside the battery while working。
Internal resistance is high, internal consumption is high, decay is accelerated, limiting the high rate of discharge; it is small and life and multipliers are better. (man/truck house quiz: ip zhiqiu)
