Lithium-ion battery and motor vehicle

Abstract

A lithium ion battery and a power vehicle are disclosed. The lithium ion battery includes a positive plate, a negative plate, an electrolyte, and a separator, the positive plate includes a positive current collector and a positive electrode material layer disposed on the positive current collector, the negative plate includes a negative current collector and a negative electrode material layer disposed on the negative current collector, the negative electrode active material of the negative electrode material layer is graphite, the positive electrode material layer includes a positive electrode active material composed of a lithium manganese iron phosphate material, a lithium iron phosphate material, and a ternary material, the mass proportions of the lithium manganese iron phosphate material, the lithium iron phosphate material, and the ternary material in the positive electrode active material are A1, A2, and A3, respectively; A1+A2+A3=1, α=(M4×η4×Y) / [(M1×η1×A1+M2×η2×A2+M3×η3×A3)×X], β=[M1×(1-η1)×A1+M2×(1-η2)×A2+M3×(1-η3)×A3]×X / [M4×(1-η4)×Y], satisfying 1.03≦α≦1.15, 0.55≦β≦1.5, X is the amount of positive electrode active material applied to the positive electrode plate, and Y is the amount of graphite applied to the negative electrode plate, in which M1, M2, M3, and M4 are all in mAh / g, and X and Y are in g.

Description

Technical Field

[0001] (Priority Information) This disclosure claims the priority of Chinese Patent Publication No. 202110320984.1, titled "Lithium-Ion Battery and Power Vehicle", filed with the China National Intellectual Property Administration on March 25, 2021, and all of its contents are incorporated herein by reference.

[0002] This disclosure relates to the technical field of batteries, specifically to lithium-ion batteries and power vehicles.

Background Art

[0003] Lithium-ion batteries are next-generation environmentally friendly and high-energy batteries, and are widely applied in fields such as electronic devices, automobiles, and aerospace. As an important component of lithium-ion batteries, the choice of the cathode material directly affects the performance of lithium-ion batteries, and mixing multiple types of cathode materials is one of the common means in the battery field.

[0004] Conventional mixing of cathode materials mainly includes mixing of lithium iron phosphate material (LFP) and ternary materials, mixing of lithium manganese iron phosphate material (LMFP) and ternary materials, and mixing of lithium manganate and ternary materials, etc. However, the former mixing means has a risk of lithium precipitation when the battery is charged at a high rate at high SOC (state of charge), which reduces the safety of the battery. The latter two mixing means can, to a certain extent, mitigate the risk of lithium precipitation when the battery is charged at a high rate, but when discharging at low SOC, it immediately reaches the cut-off voltage and the discharge power is low. In addition, lithium batteries with multiple types of cathode materials mixed have a low cathode specific capacity, which is disadvantageous for improving the battery energy density.

Summary of the Invention

[0005] In view of this, the present disclosure mixes LMFP, LFP, and ternary materials in appropriate proportions, controls the initial charge capacity, initial efficiency, etc. of the three to meet certain requirements, so that the lithium-ion batteries manufactured therefrom are less likely to precipitate lithium when charging in a high SOC state, have a large power when discharging in a low SOC state, can fully exert the specific capacity of each material, and have good cycle stability.

[0006] In a first aspect, a lithium-ion battery according to the present disclosure includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode active material of the negative electrode material layer is graphite. The positive electrode material layer includes a positive electrode active material composed of a lithium manganese iron phosphate material, a lithium iron phosphate material, and a ternary material. The mass ratios of the positive electrode active materials of the lithium manganese iron phosphate material, the lithium iron phosphate material, and the ternary material are A1, A2, and A3, respectively, and A1 + A2 + A3 = 1. α = (M4 × η4 × Y) / [(M1 × η1 × A1 + M2 × η2 × A2 + M3 × η3 × A3) × X], β = [M1 × (1 - η1) × A1 + M2 × (1 - η2) × A2 + M3 × (1 - η3) × A3] × X / [M4 × (1 - η4) × Y] is defined, 1.03 ≤ α ≤ 1.15 and 0.55 ≤ β ≤ 1.5 are satisfied. Wherein, M1 and η1 are the initial charge specific capacity and initial efficiency of the lithium manganese iron phosphate material, respectively; M2 and η2 are the initial charge specific capacity and initial efficiency of the lithium iron phosphate material, respectively; M3 and η3 are the initial charge specific capacity and initial efficiency of the ternary material, respectively; M4 and η4 are the initial discharge specific capacity and initial efficiency of the graphite, respectively; X is the coating amount of the positive electrode active material on the positive electrode plate; Y is the coating amount of the graphite on the negative electrode plate; M1, M2, M3, and M4 are all in mAh / g; X and Y are in g.

[0007] In the present disclosure, LMFP, LFP, and ternary materials are mixed to form a positive electrode active material. While adjusting the mixing ratios of the three, and by controlling the parameters α and β within a certain range in combination with battery operation aspects such as the specific capacity and initial efficiency of the positive and negative electrode active materials, a good balance of the charge and discharge characteristics of various materials can be achieved. The positive electrode active material has a high charge and discharge plateau in both high SOC states and low SOC states. Furthermore, when the battery is charged in a high SOC state, lithium is less likely to precipitate, and when discharging in a low SOC state, the power is high. And the positive electrode active material has a high tap density and can exhibit a high specific capacity, contributing to an improvement in the energy density of the lithium-ion battery. Therefore, the lithium-ion battery can achieve a good balance of good rate power performance and high energy density, etc.

[0008] In some embodiments of the present disclosure, further, γ is defined as γ=(M1×η1×A1+M2×η2×A2+M3×η3×A3)×b×c / (a×A3×1000), and 0.45≦γ≦1.55 is satisfied. Wherein, a is the residual alkali content of the ternary material, b is the liquid injection coefficient of the lithium-ion battery, with the unit of g / Ah, c is the theoretical value of the residual water content in the electrolyte of the lithium-ion battery after assembly, and a and c are calculated in ppm.

[0009] In this case, the structural stability of LFP and LMFP in the positive electrode active material is improved, iron dissolution / manganese dissolution is less likely to occur, contributing to an improvement in the cycle performance of the battery. Therefore, the lithium-ion battery can further achieve a good balance of good rate power performance, high energy density, good cycle performance, high safety, and other performances.

[0010] In some embodiments of the present disclosure, b is a constant between 2.9 and 3.8, c is a value in the range of 200 ppm to 400 ppm, and a is a value in the range of 500 ppm to 1500 ppm.

[0011] In some embodiments of the present disclosure, A2 is 2 to 5 times that of A1.

[0012] In some embodiments of the present disclosure, A1 is a value in the range of 10% to 25%.

[0013] In some embodiments of the present disclosure, the ratio of X to Y is in the range of 1.71 to 1.89.

[0014] In some embodiments of the present disclosure, the general formula of the ternary system material is LiNi x Co y M z O 2, where M is at least one metal element of Group IIIB to Group VA, 0.33 ≤ x ≤ 0.98, 0 < y < 1, 0 < z < 1, and x + y + z = 1.

[0015] In some embodiments of the present disclosure, in the lithium iron manganese phosphate material, the molar amount of manganese accounts for 0.75 to 0.9 of the sum of the molar amounts of manganese and iron.

[0016] In some embodiments of the present disclosure, the D50 particle size of the lithium iron phosphate material is 0.8 μm to 1.3 μm, the D50 particle size of the lithium iron manganese phosphate material is 10 μm to 15 μm, and the D50 particle size of the ternary system material is 4 μm to 6 μm.

[0017] In a second aspect, the power vehicle according to the present disclosure includes the lithium ion battery described in the first aspect of the present disclosure.

[0018] Regarding the advantages of the examples of the present disclosure, some are described in the following specification, some will become apparent based on the specification, or can be understood by implementing the examples of the present disclosure.

Brief Description of the Drawings

[0019] The drawings described herein are for deepening the understanding of the present disclosure, constitute a part of the present disclosure, and the exemplary embodiments and their descriptions of the present disclosure are for explaining the present disclosure and do not limit the present disclosure.

[0020]

Fig. 1a

Fig. 1b

Fig. 1c

Fig. 2

Modes for Carrying Out the Invention

[0021] The following description is an exemplary embodiment of the present invention. Those skilled in the art can make some improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also included in the protection scope of the present invention.

[0022] The lithium-ion battery according to the embodiment of the present disclosure includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode material layer provided on the positive electrode current collector. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector. The negative electrode active material of the negative electrode material layer is graphite. The positive electrode material layer includes a positive electrode active material composed of a lithium iron manganese phosphate material (LMFP), a lithium iron phosphate material (LFP), and a ternary material. The mass ratios of the positive electrode active materials of the lithium iron manganese phosphate material, the lithium iron phosphate material, and the ternary material are A1, A2, and A3, respectively, and A1 + A2 + A3 = 1. α = (M4 × η4 × Y) / [(M1 × η1 × A1 + M2 × η2 × A2 + M3 × η3 × A3) × X], β = [M1 × (1 - η1) × A1 + M2 × (1 - η2) × A2 + M3 × (1 - η3) × A3] × X / [M4 × (1 - η4) × Y] is defined, 1.03 ≤ α ≤ 1.15 and 0.55 ≤ β ≤ 1.5, wherein M1 and η1 are the initial charge specific capacity and the initial efficiency of the above-mentioned lithium iron manganese phosphate material, respectively; M2 and η2 are the initial charge specific capacity and the initial efficiency of the above-mentioned lithium iron phosphate material, respectively; M3 and η3 are the initial charge specific capacity and the initial efficiency of the above-mentioned ternary material, respectively; M4 and η4 are the initial discharge specific capacity and the initial efficiency of the above-mentioned graphite, respectively; X is the coating amount of the above-mentioned positive electrode active material on the above-mentioned positive electrode plate; Y is the coating amount of the above-mentioned graphite on the above-mentioned negative electrode plate; M1, M2, M3, and M4 are all in mAh / g, and X and Y are in g.

[0023] It should be noted that M1, M2, M3, M4, η1, η2, η3, and η4 can be obtained by testing button-type batteries made of single LMFP, LFP, ternary material, or graphite material, respectively. X and Y are parameters determined when designing the battery.

[0024] The above-mentioned α is the excess ratio of the capacity of the negative electrode plate to the capacity of the positive electrode plate. If the value of α is too small, there is a risk of lithium precipitation on the negative electrode plate during charging. If the value of α is too large, the coating amount of the negative electrode plate becomes too large, and more active lithium needs to be consumed when the SEI film (solid electrolyte interface film) is formed on the negative electrode plate, which is disadvantageous for the exertion of the capacity of the positive electrode active material and reduces the energy density of the battery. By controlling 1.03 ≤ α ≤ 1.15, the risk of lithium precipitation in the battery is reduced, and it contributes to the exertion of the capacity of the positive electrode active material. In some embodiments of the present disclosure, 1.05 ≤ α ≤ 1.12, and in some other embodiments of the present disclosure, 1.08 ≤ α ≤ 1.12.

[0025] The above β is the balance relationship of the initial efficiencies of four materials: LMFP material, LFP material, graphite, and ternary material. The initial efficiency of the ternary material < the initial efficiency of graphite < the initial efficiency of LMFP material < the initial efficiency of LFP material. When the negative electrode is graphite and only LFP material and / or LMFP material is used as the positive electrode active material, for LFP material / LMFP material, the irreversible lithium loss due to high initial efficiency is small, and the lithium consumed by graphite to form the SEI film is not sufficient. Therefore, graphite consumes other active lithium in the battery system, reduces the specific capacity of LFP / LMFP, and further reduces the energy density of the battery. On the other hand, due to the low initial efficiency of the ternary material, a large amount of irreversible lithium remaining in the negative electrode is sufficient for the negative electrode to consume to form the SEI film. When mixing LFP / LMFP and the ternary material, it is equivalent to the ternary material substantially replenishing lithium to LFP / LMFP, and the specific capacity of the entire positive electrode active material can be improved. Considering comprehensively, in the present disclosure, the value range of β is controlled to 0.55 ≦ β ≦ 1.5, which helps to improve the specific capacity of the entire positive electrode active material and contributes to the improvement of the energy density of the battery.

[0026] Also, when mixing LMFP, LFP, and ternary materials, the different charge-discharge characteristics of the three materials can be utilized. The LMFP material has a discharge plateau of a certain length in the high-voltage range (as shown in Figure 1a, the charge-discharge voltage plateau is 3.95V - 4.0V), which contributes to reducing the risk of lithium precipitation when charging at a high rate in the high SOC state of the system. The LFP material has a long charge-discharge plateau in the low-voltage range (as shown in Figure 1b, the charge-discharge voltage plateau is about 3.2V), which contributes to improving the high-power discharge performance in the low SOC state of the system. The capacity release of the ternary material is uniform throughout the voltage range (as shown in Figure 1c), and capacity release is more likely to occur in the high-voltage range. Therefore, the battery manufactured by mixing the above three materials in an appropriate ratio has a charge-discharge plateau in either the high SOC state or the low SOC state (as shown in Figure 2). In the high SOC state, LMFP and the ternary material can cooperate to discharge, the polarization of the battery is small, the battery can operate at a high rate, and the discharge power is large. However, the actual discharge current received by each material is small. Accordingly, when the battery is charged at a high rate in the high SOC state, the three can cooperate to charge, the actual charge current received by each material is small, and lithium precipitation due to overcharge is less likely to occur. In the low SOC state, LFP and LMFP can cooperate to charge and discharge, the polarization of the battery is small, the discharge power of the battery is large, which helps the electric vehicle to quickly reach a predetermined speed when starting.

[0027] Therefore, in the above lithium-ion battery according to the present disclosure, by mixing LMFP, LFP, and the ternary material in an appropriate ratio as the positive electrode active material and controlling the parameters α and β within a certain range based on the relationships such as the specific capacity and efficiency of the positive and negative electrode active materials, the battery can be provided with a high average voltage and specific capacity, which contributes to improving its energy density, reducing the risk of lithium precipitation during charging in the high SOC state of the battery, and improving the discharge power in the low SOC state.

[0028] In some embodiments of the present disclosure, further, γ = (M1×η1×A1 + M2×η2×A2 + M3×η3×A3)×b×c / (a×A3×1000) is defined, satisfying 0.45 ≤ γ ≤ 1.55, wherein, a is the residual alkali content of the ternary system material, b is the liquid injection coefficient of the lithium-ion battery, with the unit of g / Ah, c is the theoretical value of the residual water content in the electrolyte of the lithium-ion battery after assembly, and a and c are calculated in ppm.

[0029] Parameter a can be obtained by testing the ternary system material used before assembling the lithium-ion battery. Parameter b is a parameter determined when designing the battery, c is a theoretical value, and for a battery that has passed normal assembly, the residual water content c in its electrolyte is usually 200 ppm to 400 ppm. The liquid injection coefficient b is the ratio of the liquid injection amount of the battery's electrolyte to the designed discharge capacity of the battery. When the liquid injection coefficient b is determined and the battery capacity is determined, the mass of the battery's electrolyte can be determined. Further, the theoretical value of the water content in the electrolyte (calculated in g) can be known from c, and further, the mass of HF converted from water can be determined. In some embodiments of the present disclosure, b is 2.9 g / Ah to 3.8 g / Ah.

[0030] The above parameter γ can represent the suppression situation of HF in the battery electrolyte. When mixing LFP, LMFP and ternary system materials, since the ternary system material has good water absorption performance, it can preferentially consume the water remaining in the battery electrolyte and reduce the content of HF in the electrolyte. When the residual alkali content on the surface of the ternary system material and the content of HF in the electrolyte satisfy a certain relationship (i.e., 0.45 ≤ γ ≤ 1.55), the content of HF in the electrolyte can be significantly reduced, and further, the iron solubility of the LFP material and the iron manganese solubility of the LMFP material can be significantly reduced, contributing to maintaining good structural stability of these two materials, thereby improving the cycle performance of the battery and having a long cycle life. In some embodiments of the present disclosure, the range of the value of γ is 0.5 ≤ γ ≤ 1.45.

[0031] In some embodiments of the present disclosure, the above A2 is 2 to 5 times that of A1. In this case, it can be guaranteed that the lithium-ion battery has higher charge and discharge power at different SOC states and better safety performance. In some embodiments of the present disclosure, the above A2 is 2.4 to 3.5 times that of A1.

[0032] In some embodiments of the present disclosure, the above A1 is a value in the range of 10% to 25%. In some other embodiments of the present disclosure, the above A1 is 15% to 25%. In some still other embodiments of the present disclosure, the above A1 is 15% to 22%. In some embodiments of the present disclosure, the above A2 is a value in the range of 45% to 80%. In some other embodiments of the present disclosure, the above A2 is 45% to 75%. In some still other embodiments of the present disclosure, the above A2 is 50% to 75%. In some embodiments of the present disclosure, the above A3 is a value in the range of 10% to 40%. In some other embodiments of the present disclosure, the above A3 is 10% to 30%. In some still other embodiments of the present disclosure, the above A3 is 10% to 25%.

[0033] In some embodiments of the present disclosure, the ratio of X to Y (X / Y) is in the range of 1.71 to 1.89. Thereby, not only can the lithium precipitation during charging of the negative electrode plate be avoided, but it also contributes to the exertion of the capacity of the positive electrode active material and helps to improve the energy density of the battery. In some other embodiments of the present disclosure, X / Y is 1.73, 1.82 or 1.87, etc.

[0034] In the present disclosure, the general formula of the ternary system material is LiNi x Co y M z OIt is 2, M is at least one metal element of Group IIIB to Group VA, 0.33 ≦ x ≦ 0.98, 0 < y < 1, 0 < z < 1, and x + y + z = 1. For example, M is at least one of Mn, Al, Zr, Ti, Y, Sr, and W. In some embodiments of the present disclosure, y satisfies 0.01 ≦ y ≦ 0.33, and z satisfies 0.01 ≦ z ≦ 0.33.

[0035] In some embodiments of the present disclosure, the value range of x is 0.70 ≦ x ≦ 0.98. Also, when the value of x is high, the ternary system material is also called a "high nickel ternary system material", which has high water absorption, high specific capacity and good rate performance, has an H2-H3 phase transition at about 4.1 to 4.15V, has an obvious charge and discharge plateau, and contributes to the collaborative discharge of LMFP and the high nickel ternary system material. In some other embodiments of the present disclosure, the value range of x is 0.80 ≦ x ≦ 0.90, and in some other embodiments of the present disclosure, the value range of x is 0.83 ≦ x ≦ 0.88.

[0036] The nickel element in the ternary system material is alkaline. When exposed to air, it is easy to absorb water and carbon dioxide, and reacts with the surface layer lithium to generate lithium hydroxide (LiOH) and lithium carbonate (Li2CO3). The residual alkali content of the ternary system material is specifically the percentage of the mass of LiOH and Li2CO3 measured before assembling the battery in the total mass of the ternary system material. In some embodiments of the present disclosure, the above a is a value in the range of 500 ppm to 1500 ppm.

[0037] In some embodiments of the present disclosure, in the above lithium manganese iron phosphate material, the molar amount of manganese accounts for 0.75 to 0.9 of the sum of the molar amounts of manganese and iron. That is, the general formula of lithium manganese iron phosphate is LiMn k Fe 1-kIt can be written as PO4, where 0.75 ≤ k ≤ 0.9. In this case, since the molar ratio of the manganese element is large, the charging voltage plateau of the lithium iron manganese phosphate material at 4.05 - 4.1 V becomes longer, contributing to reducing the risk of lithium precipitation when the battery is charged at a high rate with a high SOC.

[0038] In some embodiments of the present disclosure, the particle size D50 of the ternary material is 4 μm - 6 μm, for example, 4 μm - 5 μm. In some other embodiments of the present disclosure, the ternary material is a quasi-single crystal material, and its structural stability is higher than that of the ternary material in an aggregated state.

[0039] In some embodiments of the present disclosure, the particle size D50 of the lithium iron phosphate material is 0.8 μm - 1.3 μm, for example, 0.8 μm - 1.2 μm.

[0040] In some embodiments of the present disclosure, the particle size D50 of the lithium iron manganese phosphate material is 10 μm - 15 μm.

[0041] Furthermore, in order to improve the conductivity of the lithium iron phosphate or lithium iron phosphate material, it further has a carbon coating layer on its surface. Furthermore, the carbon content in the lithium iron phosphate or lithium iron phosphate material is 0.8 wt% - 1.2 wt%.

[0042] The positive electrode material layer and the negative electrode material layer further include a conductive agent and a binder. For example, the positive electrode material layer may be formed by applying and drying a positive electrode slurry containing the positive electrode active material, a conductive agent, a binder, and a solvent. When preparing the positive electrode slurry, first mix the binder and the solvent, stir well, then add the conductive agent, stir, and then add the positive electrode active material, stir, and then pass through a sieve. The added positive electrode active material may be a direct mixture of the above LMFP, LFP, and ternary material, or a batch addition of these three materials.

[0043] In some embodiments of the present disclosure, the mass ratio of the above positive electrode active material in the positive electrode material layer is 95% to 97%. In some other embodiments of the present disclosure, the mass ratio of the above graphite in the negative electrode material layer is 95% to 98%.

[0044] In some embodiments of the present disclosure, due to the above positive electrode active material, the maximum consolidation density of the above positive electrode plate may be 2.7 g / cm 3 ~2.8 g / cm 3 .

[0045] The conductive agent and the binder are both common selections in the field of batteries. For example, the conductive agent may be at least one of carbon nanotubes, carbon fibers, carbon black (e.g., acetylene black, ketjen black), furnace black, and graphene, but is not limited thereto. In some embodiments of the present disclosure, the above conductive agent includes three types of carbon nanotubes, carbon black, and graphene, and the three types of conductive agents can provide good conductivity to the positive electrode material layer. Furthermore, the mass ratio of carbon nanotubes, carbon black, and graphene may be 6:5:2.

[0046] The binder may be one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), poly(acrylic acid) (PAA), polyacrylate, polyolefin (e.g., polyethylene, polypropylene, polystyrene), sodium carboxymethyl cellulose (CMC), and sodium alginate. PVDF may be a copolymer obtained by copolymerizing vinylidene fluoride and an olefin-based compound containing a polar group, and the polar group includes at least one of a carboxyl group, an epoxy group, a hydroxy group, and a sulfonic acid group. Due to the presence of the polar group, the peel strength between the positive electrode material layer or the negative electrode material layer and the current collector can be improved.

[0047] The above-mentioned positive current collector and negative current collector may each independently be selected from a metal foil material or an alloy foil material. The metal foil material includes a copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, or silver foil material, and the alloy foil material includes stainless steel or an alloy containing at least one element of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold, and silver.

[0048] In some embodiments of the present disclosure, the alloy foil material has the above elements as main components. The metal foil material may further contain doping elements, and the doping elements include, but are not limited to, one or more of platinum, ruthenium, iron, cobalt, gold, copper, zinc, aluminum, magnesium, palladium, rhodium, silver, and tungsten. The positive current collector and the negative current collector can be subjected to an etching treatment or a roughening treatment to form a secondary structure in order to effectively contact the electrode material layer. Generally, an aluminum foil is usually used as the positive current collector, and a copper foil is usually used as the negative current collector.

[0049] The power vehicle according to an embodiment of the present disclosure includes the above lithium-ion battery. Due to the use of the lithium-ion battery, the power vehicle can quickly reach full charge when charging at a charging post, can quickly reach a high starting speed when starting, the battery has high endurance and high safety.

[0050] Hereinafter, embodiments of the present disclosure will be further described with reference to a plurality of specific examples.

[0051] The LMFP material used in the embodiments of the present disclosure is LiMn 0.8 Fe 0.2 PO4, the particle size D50 is 10 - 15 μm, the initial charge specific capacity M1 is 160 mAh / g, the initial efficiency η1 is 96%, the LFP material used has a particle size D50 of 0.8 - 1.2 μm, the initial charge specific capacity M2 is 162 mAh / g, and the initial efficiency η2 is 99%. The ternary material is a high-nickel ternary single-crystal-like material, and the general formula is LiNi 0.83Co 0.12 Mn 0.05 wherein the particle size D50 is 4 - 5 μm, the initial charge specific capacity M3 is 238 mAh / g, the initial efficiency η3 is 86%, and the residual alkali content a is 700 ppm. The specific capacity of the first discharge of the graphite is M4 = 355 mAh / g, and the initial efficiency η4 is 95%. The injection coefficient b of the battery to be assembled is 3.1 g / Ah, and the theoretical value of the residual water content c in the electrolyte after the battery is assembled is designed to be 200 ppm.

[0052] Preparation of the positive electrode active material: The LMFP material, the LFP material, and the ternary material are mixed at the mixing ratios A1, A2, and A3 shown in Table 1 respectively to obtain the positive electrode active materials of each example. As shown in Table 1, the ratio of the coating amount X of the positive electrode active material on the positive electrode plate to the coating amount Y of the graphite on the negative electrode plate is controlled. Based on the above formula, the parameters γ, α, and β are determined, and the related experimental parameters are summarized in Table 1.

[0053] In addition, in order to highlight the beneficial effects of the technical means of the present disclosure, Comparative Examples 1 - 4 shown in Table 1 below are further provided. (Table 1) Some parameters of each example and comparative example

Table 1

[0054] Manufacture of the positive electrode plate: The organic solvent NMP and the binder PVDF are added to a stirrer and stirred for 1 h. Then, a conductive agent (specifically, a mixture of carbon nanotubes, carbon black, and graphene with a mass ratio of 6:5:2) is added and stirred for 30 min. Then, the positive electrode active materials of each example or comparative example are added respectively and stirred for 3 h, and then sieved to obtain the positive electrode slurries of each example and comparative example. In each positive electrode slurry, the mixing mass ratio of the positive electrode active material, the conductive agent, the binder PVDF, and the organic solvent NMP is 100:2:2:30.

[0055] The positive electrode slurries of each example and comparative example were respectively coated on the surfaces on both sides of the aluminum foil. After removing NMP by high-temperature baking, a positive electrode material layer was formed on the aluminum foil, and then roll-pressed and slit to obtain a double-sided positive electrode plate with a surface density of 4.0 g / dm 2 on both sides. Based on the surface density and thickness of the double-sided Positive positive electrode plate, the consolidation density of the positive electrode plate was calculated, and the results are summarized in Table 2.

[0056] In a similar manner, the positive electrode slurries of each example and comparative example were respectively coated on the surface on one side of the aluminum foil. After removing NMP by high-temperature baking, a positive electrode material layer was formed on the aluminum foil, and then roll-pressed and slit to obtain a single-sided positive electrode plate with a surface density of 2.0 g / dm 2 .

[0057] Manufacture of the negative electrode plate: Graphite, conductive carbon black Supper P, binder SBR, binder CMC and water were mixed at a mass ratio of 100:1.0:2.5:1.1:105 to obtain a negative electrode slurry. The negative electrode slurry was coated on the surfaces on both sides of the copper foil. After removing water by high-temperature baking, a negative electrode material layer was formed on the copper foil, and then roll-pressed and slit to obtain a double-sided negative electrode plate with a surface density of 2.1 g / dm 2 and a consolidation density of 1.60 g / cm 3 .

[0058] Assembly of the battery: The double-sided positive electrode plates of each example and comparative example and the double-sided 2 negative electrode plate with the above surface density of 2.1 g / dm were prepared and assembled using a PP film as the separator to obtain a 053450 full cell.

[0059] The single-sided positive electrode plates of each example and comparative example were prepared. Using a metallic lithium plate as the negative electrode, a Celgard 2300 microporous membrane as the separator, and a solution of 1.0 mol / L LiPF6 in ethylene carbonate (EC):dimethyl carbonate (DMC)=1:1~5 (volume ratio) as the electrolyte, a CR2025 button-type battery was assembled in a glove box.

[0060] To strongly support the beneficial effects of the present disclosure, the trigger temperatures of thermal runaway of the cathode materials of the button-type batteries in each example and comparative example were measured, and the capacity retention rates of the full cells in each example and comparative example after 2000 cycles at 45 °C and the contents of Fe and Mn eluted into the anode were measured, and the results are summarized in Table 2.

[0061] The method for measuring the trigger temperature of thermal runaway of the cathode material is as follows. Prepare the button-type batteries in each example and comparative example. First, fully charge each button-type battery (specifically, first charge at a constant current of 0.1C until the cut-off voltage reaches 4.2V, then charge at a constant voltage of 4.2V, and the cut-off current is 0.05C), make the cathode plate in a state of complete lithium desorption. Then, disassemble the button-type battery, take out the cathode plate, mix the cathode material of the cathode plate and the electrolyte at a certain mass ratio, put it into a high-temperature crucible, heat it at a heating rate of 5 °C / min, measure its thermogram with a differential scanning calorimeter (DSC), and observe the trigger temperature of thermal runaway of the cathode material.

[0062] The method for measuring the capacity retention rate after 2000 cycles at 45 °C is as follows. At 45 °C, charge the full cells in each example and comparative example at a constant current of 1C until the voltage reaches 4.1V, then charge at a constant voltage of 4.1V, and the cut-off current is 0.05C. Then, discharge at a constant current of 1C until the voltage reaches 2.5V. In this way, after performing charge and discharge 2000 cycles, calculate the ratio of the 2000th discharge capacity of the battery to the first discharge capacity, and this ratio is taken as the capacity retention rate of the battery after 2000 cycles.

[0063] The method for measuring the charge and discharge power characteristics at different SOCs is as follows.

[0064] 1. Charge the full cells in each example and comparative example at a constant current of 0.2C until 4.2V, leave it for 5 minutes, discharge at a constant current of 0.2C until 2.5V, leave it for 5 minutes, cycle 2 times, record the second discharge capacity as C0, and adjust the SOC with this capacity.

[0065] 2. Charge each full cell at a constant current of 0.2C until 4.2V, leave it for 30 min, discharge it at a constant current of 0.2C until the specified SOC (specifically, 20% of the SOC when charging the full cell at a constant current of 0.2C until 4.2V), and then discharge it at different discharge currents. 1. Discharge at a constant current of 0.5C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 75 s, leave it for 5 min, and adjust the SOC to 20%. 2. Discharge at a constant current of 1C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 150 s, leave it for 5 min, and adjust the SOC to 20%. 3. Discharge at a constant current of 2C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 300 s, leave it for 5 min, and adjust the SOC to 20%. 4. Discharge at a constant current of 3C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 450 s, leave it for 5 min, and adjust the SOC to 20%. 5. Discharge at a constant current of 5C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 750 s, leave it for 5 min, and adjust the SOC to 20%. 6. Discharge at a constant current of 7C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 1050 s, leave it for 5 min, and adjust the SOC to 20%. 7. Discharge at a constant current of 10C for 30 s, leave it for 5 min, record the discharge cut-off voltage, then charge at a constant current of 0.2C for 1500 s, leave it for 5 min, and adjust the SOC to 20%. Based on the above 7 sets of measured data, fit the relational expression between the discharge cut-off voltage and the discharge current. Furthermore, based on the discharge cut-off voltage V0 (specifically, 2.5V) of the battery designed by the inventors, calculate the current I0 required to discharge to the set cut-off voltage V0 over a certain discharge time, and obtain the discharge peak power P0 = V0 * I0.

[0066] 3. At room temperature, discharge each full cell at a constant current of 0.2C until 2.5V, leave it for 30 min, charge it at a constant current of 0.2C until the specified SOC (specifically, 80% of the SOC when the full cell is discharged at a constant current of 0.2C until 2.5V), and then charge it with different charging currents. 1. Charge it at a constant current of 0.5C for 30 s, leave it for 5 min, record the charge cut-off voltage, then discharge it at a constant current of 0.2C for 75 s, leave it for 5 min, and adjust the SOC to 80%. 2. Charge it at a constant current of 1C for 30 s, leave it for 5 min, record the charge cut-off voltage, then discharge it at a constant current of 0.2C for 150 s, leave it for 5 min, and adjust the SOC to 80%. 3. Charge it at a constant current of 2C for 30 s, leave it for 5 min, record the charge cut-off voltage, then discharge it at a constant current of 0.2C for 300 s, leave it for 5 min, and adjust the SOC to 80%. 4. Charge it at a constant current of 3C for 30 s, leave it for 5 min, record the charge cut-off voltage, then discharge it at a constant current of 0.2C for 450 s, leave it for 5 min, and adjust the SOC to 80%. 5. Charge it at a constant current of 5C for 30 s, leave it for 5 min, record the charge cut-off voltage, then discharge it at a constant current of 0.2C for 750 s, leave it for 5 min, and adjust the SOC to 80%. Based on the above five sets of measured data, fit the relational expression between the charge cut-off voltage and the charging current. Further, based on the charge cut-off voltage V0’ (specifically, 4.2V) of the battery designed by the inventors, calculate the current I0’ required to charge to the set cut-off voltage V0’ over a certain charging time, and obtain the charging peak power P0’ = V0’ * I0’.

[0067] In addition, the measurement methods of M1 and η1 of the LMFP material mentioned above are as follows. The LMFP positive electrode plate with a single-sided surface density of 2.0 g / dm 2 is manufactured in the above manner (the positive electrode active material contains only LMFP), and the tap density of the positive electrode plate is 2.5 g / cm 3To this extent. An LMFP positive electrode plate, a metallic lithium plate, a separator, and a certain mass of electrolyte are assembled in a glove box to obtain a CR2025 button-type battery. The button-type battery is left standing for about 4 h to sufficiently soak the electrode plate in the electrolyte. The button-type battery is charged at a constant current of 0.1 C until the voltage reaches 4.3 V, then charged at a constant voltage of 4.3 V until the cut-off current reaches 0.01 C, and then discharged at a constant current of 0.1 C until the voltage reaches 2.0 V. The ratio of the discharge capacity to the charge capacity in the first cycle is defined as the first-cycle efficiency η1, and the ratio of the charge capacity in the first cycle to the mass of the LMFP active material in the electrode plate is defined as the first-cycle charge specific capacity M1 of the LMFP material.

[0068] The measuring methods for M2 and η2 of the above LFP material are as follows. An LFP positive electrode plate (the positive electrode active material contains only LFP) with a single-sided surface density of 2.0 g / dm 2 is manufactured, and the tap density of the positive electrode plate is about 2.6 g / cm 3 To this extent. An LFP positive electrode plate, a metallic lithium plate, a separator, and a certain mass of electrolyte are assembled in a glove box to obtain a CR2025 button-type battery. The button-type battery is left standing for about 4 h to sufficiently soak the electrode plate in the electrolyte. The button-type battery is charged at a constant current of 0.1 C until the voltage reaches 3.8 V, then charged at a constant voltage of 3.8 V until the cut-off current reaches 0.01 C, and then discharged at a constant current of 0.1 C until the voltage reaches 2.0 V. The ratio of the discharge capacity to the charge capacity in the first cycle is defined as the first-cycle efficiency η2, and the ratio of the charge capacity in the first cycle to the mass of the LFP active material in the electrode plate is defined as the first-cycle charge specific capacity M2 of the LFP material.

[0069] The measuring methods for M3 and η3 of the above ternary system material are as follows. A ternary system positive electrode plate with a single-sided surface density of 2.0 g / dm 2 is manufactured, and the tap density of the positive electrode plate is about 3.5 g / cm 3 To this extent, and the positive electrode active material of the positive electrode plate is a ternary system material LiNi 0.83 Co 0.12 Mn 0.05It only contains. Assemble a CR2025 button-type battery with the ternary cathode plate, lithium plate, separator and a certain mass of electrolyte in a glove box. Leave the button-type battery standing for about 4 h to fully immerse the electrode plate in the electrolyte. Charge the button-type battery at a constant current of 0.1 C until 4.3 V, and then charge it at a constant voltage of 4.3 V until the cut-off current reaches 0.01 C, and discharge it at a constant current of 0.1 C until 3.0 V. Let the ratio of the discharge capacity to the charge capacity in the first cycle be the first-cycle efficiency η3, and let the ratio of the charge capacity in the first cycle to the mass of the active material of the electrode plate be the first-cycle charge capacity M3 of the high-nickel ternary material.

[0070] The measurement methods of M4 and η4 of the above graphite are as follows. The graphite electrode plate with a single-sided surface density of 1.05 g / dm 2 is manufactured in the above manner, and the consolidation density of the graphite electrode plate is about 1.60 g / cm 3 Assemble a CR2025 button-type battery with the graphite electrode plate, lithium plate, separator and a certain mass of electrolyte in a glove box. Leave the button-type battery standing for about 4 h to fully immerse the electrode plate in the electrolyte. For the button-type battery, (1) discharge it at a constant current of 0.1 C until 0.005 V, (2) discharge it at constant currents of 0.09 C, 0.08 C... 0.02 C until 0.001 V, (3) leave it standing for 15 min, (4) charge it at a constant current of 0.1 C until 1.5 V, and (5) leave it standing for 15 min. Let the ratio of the charge capacity to the discharge capacity in the first cycle be the first-cycle efficiency η4, and let the ratio of the discharge capacity in the first cycle to the mass of the active material of the electrode plate be the first-discharge capacity M4 of the graphite material. (Table 2) Measurement results of the cathode plates and battery performance of each example and comparative example

Table 2

[0071] As can be seen from Table 1 and Table 2, in Comparative Example 1, both LFP and the ternary material are mixed, LMFP is not involved, the charging power at a high SOC state is low, only 300 W / g, and the addition ratio of the ternary material is too high, reaching 65%, resulting in a significant decline in the safety performance of the battery, the start temperature of its thermal runaway drops to 250 °C, and the cycle performance of the whole battery also deteriorates.

[0072] In Comparative Example 2, both LMFP and the ternary material are mixed, the LFP material is not involved, the discharge power in the low SOC state is low, only 300 W / g, and the addition ratio of the ternary material is too high, so there are the same problems as in Comparative Example 1. LMFP has worse cycle performance than the LFP material. The capacity retention rate of the full cell in Comparative Example 2 after 2000 cycles at 45°C is lower than that of Comparative Example 1, only 70%.

[0073] In Comparative Example 3, two materials, LMFP and LFP, are mixed and the ternary material is not involved. Since the battery in Comparative Example 3 has no ternary material to suppress the presence of HF in the electrolyte and further suppress the elution of Mn and Fe, its cycle performance is the worst, and the capacity retention rate drops to 60% after 2000 cycles at 45°C.

[0074] In Comparative Example 4, three kinds of cathode active materials are mixed, but their mixing ratios do not satisfy 1.03 ≦ α ≦ 1.15 and 0.55 ≦ β ≦ 1.5 of the requirements of the present disclosure. The battery in Comparative Example 4 has low charging power in the high SOC state and low discharge power in the low SOC state. Also, the addition ratio of the ternary material is too high, and the safety performance and cycle performance are reduced to different degrees.

[0075] As can be seen from Table 2, in the cathode active material formed by mixing the LMFP material, the LFP material and the ternary material, when the above α is 1.03 - 1.15 and β is 0.55 - 1.5 according to the mixing ratio of the three, both the discharge power at low SOC and the charging power at high SOC of the battery are large. The discharge power at low SOC is 1400 W / g or more, the charging power at high SOC is 600 W / g or more, the compaction density of the cathode plate is high, the structural stability of the cathode material is high, the cycle performance of the battery is high, and the safety is high. Also, when γ is in the range of 0.45 - 1.55, the battery has better comprehensive performance.

[0076] The above embodiments merely illustrate some embodiments of the present disclosure, and although the description is specific and detailed, it should not be understood as limiting the patent scope of the present disclosure. For those skilled in the art, several further modifications and improvements can be made on the premise of not departing from the concept of the present disclosure, and all of these belong to the protection scope of the present disclosure. Therefore, the patent protection scope of the present disclosure should be based on the appended claims.

Claims

1. A lithium-ion battery including a positive electrode plate, a negative electrode plate, an electrolytic solution, and a separator disposed between the positive electrode plate and the negative electrode plate, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, the negative electrode active material of the negative electrode material layer is graphite, the positive electrode material layer includes a positive electrode active material composed of a lithium manganese iron phosphate material, a lithium iron phosphate material, and a ternary material, and the mass ratios of the positive electrode active materials of the lithium manganese iron phosphate material, the lithium iron phosphate material, and the ternary material are A １ , A ２ and A ３ respectively, and A １ +A ２ +A ３ = 1 α = (M ４ × η ４ × Y) / [(M １ × η １ × A １ + M ２ × η ２ × A ２ + M ３ × η ３ × A ３ ) × X], β = [M １ × (1 - η １ ) × A １ + M ２ × (1 - η ２ ) × A ２ + M ３ × (1 - η ３ ) × A ３ × X / [M ４ × (1 - η ４ ) × Y] is defined as, 1.03 ≤ α ≤ 1.15 and 0.55 ≤ β ≤ 1.5, and wherein, M １ , η １ are the initial charge specific capacity and the initial efficiency of the lithium iron manganese phosphate material, respectively, M ２ , η ２ are the initial charge specific capacity and the initial efficiency of the lithium iron phosphate material, respectively, M ３ , η ３ are the initial charge specific capacity and the initial efficiency of the ternary material, respectively, M ４ , η ４ are the initial discharge specific capacity and the initial efficiency of the graphite, respectively, X is the coating amount of the positive electrode active material on the positive electrode plate, Y is the coating amount of the graphite on the negative electrode plate, and the M １ , M ２ , M ３ , M ４ all have the unit of mAh / g, and the X and Y have the unit of g further, γ is defined as γ = (M1 × η1 × A1 + M2 × η2 × A2 + M3 × η3 × A3) × b × c / (a × A3 × 1000), and 0.45 ≤ γ ≤ 1.55, where a is the residual alkali content of the ternary material, b is the liquid injection coefficient of the lithium-ion battery, with the unit g / Ah, c is the theoretical value of the residual water content in the electrolyte of the lithium-ion battery after assembly, and a and c are calculated in ppm, lithium-ion battery.

2. The aforesaid A ２ is １ 2 to 5 times that of A. The lithium ion battery according to claim 1.

3. Said A １ is a value in the range of 10% to 25%, the lithium ion battery according to claim 1 or 2.

4. The ratio of X to Y is a value in the range of 1.71 to 1.89, the lithium-ion battery according to any one of Claims 1 to 3.

5. b is a constant between 2.9 and 3.8, c is a value in the range of 200 ppm to 400 ppm, and a is a value in the range of 500 ppm to 1500 ppm, the lithium-ion battery according to Claim 1.

6. The general formula of the ternary system material is LiNi ｘ Co ｙ M ｚ O₂, wherein M is at least one metal element of Group IIIB to Group VA, 0.33 ≤ x ≤ 0.98, 0 < y < 1, 0 < z < 1, and x + y + z = 1. The lithium-ion battery according to any one of claims 1 to 5.

7. In the lithium iron manganese phosphate material, the molar amount of manganese accounts for 0.75 to 0.9 of the sum of the molar amounts of manganese and iron, the lithium-ion battery according to any one of Claims 1 to 6.

8. The D50 particle size of the lithium iron phosphate material is 0.8 μm to 1.3 μm, the D50 particle size of the lithium iron manganese phosphate material is 10 μm to 15 μm, and the D50 particle size of the ternary material is 4 μm to 6 μm, the lithium-ion battery according to any one of Claims 1 to 7.

9. A power vehicle including the lithium-ion battery according to any one of Claims 1 to 8.

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