Lithium battery using much less maximum capacity is what reason?

Source: 2020 - 03 - 28 14:27 hits: times the maximum capacity of lithium-ion batteries and decreased with the increase of consumption is the cause of what? Common household rechargeable batteries, such as lithium battery and nickel cadmium, nickel metal hydride batteries and its maximum capacity decreased with the use of time. What reason is this? Hoist the lithium battery experts today to just take you to discuss: internal and external causes: 1. Internal reason ( 1) In electrode, repeatedly charge and discharge can reduce the surface of the electrode active products, to improve the current density, increasing polarization; Changed the structure of the active material. Active particles electric contact, or even decline. Electrode data ( Including the collector fluid) The corrosion; At present commonly used battery negative graphite, very anode LiCoO2, LiMn2O4, lithium iron phosphate batteries will be some initial electrolyte on the electrode surface to form a layer of SEI ( Solid electrolyte membrane, its composition is mainly ROCO2Li (carbonate EC and PC circulation recovery products) And ROCO2Li ROLi carbonate ( DEC, DMC chain products) Recovery, Li2CO3 ( Residual water and ROCO2Li reaction products) , if you use LiPF6, high frequency residual and SEI ROCO2Li, SEI is primarily a LiF and ROLi. SEI li + conductor, when to take off the intercalated-li carbon electrode volume change is very small, but even small, its internal stress will lead to break the negative, exposing new carbon appearance and solvent reaction of SEI, which constitutes the lithium ions and electrolyte, and the degree of positive data in a certain active substance is puffy do not touch the loss correction permanent structure, therefore, the consumption of positive and negative form the ability of decreasing; In addition, add SEI will form the resistance of the interface layer framework, increase the electrochemical reaction of polarization potential, attenuation in electrode, constitute the function of the battery with the response of the charge and discharge, the function of the binder will gradually decline, the strength of the bonding agent will decline, so that the electrode data. Copper foil and aluminum foil is the commonly used negative and positive electrode collector fluid, both of which are prone to corrosion, and corrosion products assembled on the surface of the collector liquid membrane, increase resistance, copper ions can also form the dendrite, penetrating crack, the battery failure. ( 2) In terms of electrolyte solution, electrolyte or differentiation resulting in a decline in the conductivity of conductive salt, this divergence form interface passivation; Lithium ion battery liquid electrolyte by solute (commonly Such as LiPF6, LiBF4, LiClO4 lithium) , solvent, and special additives. The electrolyte has good ionic conductivity and electrical insulation, and conduction current between the positive and negative. After the first charge and discharge, overcharge and overdischarge, long cycle, the degradation of the electrolyte effect will occur in lithium ion battery, with the generation of gas, gas composition is relatively chaos, it can't eliminate a reaction after the battery. Then add the battery charge and discharge. Due to the oxidation and corrosion of data electrode consumes part of electrolyte, causing shortages of electrolyte electrode can't flush to the electrolyte, resulting in electrochemical reaction is not completely, make the battery capacity can not meet the requirement of the planning. ( 3) Barrier, jam or damage to the battery internal short circuit is the role of the barrier such as a battery of the positive and negative, in order to prevent the short circuit directly between the north and south poles. In the process of lithium ion battery cycle, diaphragm gradually dry, failure is the important reason for the declining in the early days of cell function. This is mainly due to dry as the electrolyte in the barrier, solution resistance increases, the electrochemical stability of the barrier and mechanical performance degradation, electrolyte wettability in the process of being recharged. Because clearance dry battery ohm resistance increase, incomplete discharge in the repeated overcharge your battery capacity, battery capacity could not return to the initial state, greatly reducing the discharge capacity and service life of the battery. 2. The external reason ( 1) Rapid charge and discharge in the case of fast charging, the current density is too large, the cathode polarization is serious, the accumulation of lithium will be more obvious, the copper foil in the copper foil and carbon border of active material brittle, easy to crack. Spontaneous battery winding is limited by a fixed space, copper foil not free to tensile stress. Under the action of stress, crack extension and expansion of the original, copper foil fracture due to the expansion of space. ( 2) Temperature when the temperature significantly higher than the room temperature, the first concern is the thermal stability of the organic electrolyte, including organic electrolyte itself and the thermal stability of the thermal stability of interaction between electrode and electrolyte. It is generally believed that the positive/organic electrolyte reaction is the influence of main factors on the safety of kk ion battery. Due to the positive electrode and the electrolyte reaction kinetics is very fast, so control the whole of the thermal performance of the battery. If the battery of the ambient temperature is high enough to cause the reaction of the electrolyte, will lead to the thermal runaway of the battery, even fire and explosion. The size of the discharge current will directly affect the discharge capacity of lithium ion batteries. Under the condition of large current discharge, not only there are serious electrolyte interfacial polarization, there are also active body into ions and the spread of the electrode polarization. ( 3) Depth charge discharge for a long time to be transferred from the internal structure, one is the formation of electrolyte excessive evaporation, 2 it is lithium battery cathode excessive response to the change of the dielectric film, its composition ability demoulding, constitute a permanent capacity loss; Charging mainly from the middle of the night of voltage stability and power grid voltage rise, the charger has stopped charging, voltage rise, will continue to collect fees, overcharging change capacity loss results in the formation of the battery anode data structure, the differentiation of oxygen and the electrolyte severe oxidation and burning explosion; Organic solvent/electrolyte electrolyte of lithium salt; The cathode of lithium ion precipitation leads to the cathode copper ions dissolved, the positive form of copper dendrite. ( 4) Feeling is typically process and impact, such as welding is firm or not, whether the internal circuit planning reasonable relations, etc.