WO2022089509A1 - 锂离子电池 - Google Patents

锂离子电池 Download PDF

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WO2022089509A1
WO2022089509A1 PCT/CN2021/126905 CN2021126905W WO2022089509A1 WO 2022089509 A1 WO2022089509 A1 WO 2022089509A1 CN 2021126905 W CN2021126905 W CN 2021126905W WO 2022089509 A1 WO2022089509 A1 WO 2022089509A1
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lithium
ion battery
positive electrode
active material
electrode active
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French (fr)
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陈娜
郝嵘
潘仪
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BYD Co Ltd
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BYD Co Ltd
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Priority to KR1020237015865A priority Critical patent/KR102928860B1/ko
Priority to EP21885236.6A priority patent/EP4224574A4/en
Priority to CA3196755A priority patent/CA3196755A1/en
Priority to JP2023526182A priority patent/JP7522932B2/ja
Publication of WO2022089509A1 publication Critical patent/WO2022089509A1/zh
Priority to US18/309,235 priority patent/US20230268515A1/en
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M2010/4292—Aspects relating to capacity ratio of electrodes/electrolyte or anode/cathode
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of power equipment, and in particular, the present application relates to a lithium ion battery.
  • Lithium manganese iron phosphate (LMFP for short) cathode material has become the mainstream cathode material for lithium-ion batteries due to its high structural stability, good cycle performance and safety performance.
  • the embodiment of the present application provides a lithium ion battery to solve the problem that the capacity of lithium manganese iron phosphate is difficult to effectively exert in the specific capacity of the traditional lithium ion battery.
  • the embodiment of the present application provides a lithium-ion battery, including:
  • the actual specific capacity of lithium manganese iron phosphate in the positive electrode sheet of the lithium ion battery in the full battery is greater than 138 mAh/g.
  • the lithium ion battery further includes an electrolyte, and the lithium ion battery satisfies the following formula:
  • a is the residual alkali content of the ternary material
  • b is the liquid injection coefficient of the lithium ion battery
  • c is the residual H 2 O content in the electrolyte
  • the value range of a is 500ppm-1500ppm
  • the value range of the b is 2.9g/Ah-3.8g/Ah
  • the value range of the c is 200ppm-400ppm.
  • the Mn dissolution amount of the lithium ion battery at 45° C. and 2000 charge-discharge cycles is less than 700 ppm.
  • the lithium-ion battery satisfies the following formula:
  • the ratio of the y to the x ranges from 0.52 to 0.58.
  • the value of A 1 ranges from 75% to 95%.
  • the general formula of the ternary material is LiNi a1 Co b1 X c1 O 2 ;
  • the X is at least one metal element in the III subgroup to the V main group.
  • the mole ratio of Ni in the ternary material ranges from 80% to 95%.
  • the positive electrode active material on the positive electrode sheet in the lithium ion battery provided by the embodiment of the present application is a mixture of ternary material and lithium iron manganese phosphate material, and the lithium iron manganese phosphate and the ternary material and the negative electrode active material graphite satisfy the above formula (1) and The relationship in formula (2), so that the first efficiency of the mixed positive electrode active material and the first efficiency of the graphite material are balanced, ensuring that the capacity of lithium manganese iron phosphate can be effectively exerted, and thus ensuring the high safety of lithium ion batteries. On the basis of the properties, the energy density and cycle performance of lithium-ion batteries are improved.
  • Figure 1 shows the cyclic voltammetry (CV) curves of ternary material, LFMP and ternary material and LFMP mixed material;
  • Figure 2 shows the first charge-discharge cycle curves of ternary materials, LFMP, and ternary materials and LFMP mixed materials.
  • first, second and the like in the description and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances so that the embodiments of the present application can be practiced in sequences other than those illustrated or described herein, and distinguish between “first”, “second”, etc.
  • the objects are usually of one type, and the number of objects is not limited.
  • the first object may be one or more than one.
  • “and/or” in the description and claims indicates at least one of the connected objects, and the character “/" generally indicates that the associated objects are in an "or” relationship.
  • the positive electrode active material of the positive electrode sheet includes LMFP (lithium manganese iron phosphate) and a ternary material
  • the negative electrode active material of the negative electrode sheet is graphite
  • the lithium ion battery satisfies the following formula:
  • M 1 is the first charge specific capacity of the LMFP, in mAh/g, ⁇ 1 is the first efficiency of the LMFP, A 1 is the mass percentage of LMFP in the positive electrode active material, and M 2 is the ternary material
  • the first charge specific capacity, in mAh/g, ⁇ 2 is the first efficiency of the ternary material
  • a 2 is the mass percentage of the ternary material in the positive electrode active material
  • M 3 is the first discharge specific capacity of the graphite
  • the unit is mAh/g
  • n is the first efficiency of the graphite
  • x is the dressing amount of the positive electrode active material
  • y is the dressing amount of the negative electrode active material
  • the units of x and y are the same, and the ratio of y and x
  • the range is 0.52-0.58.
  • the first efficiency is the ratio of the first discharge capacity to the first charge capacity of the coin cell; for the negative electrode active material, the first efficiency is the ratio of the first charge capacity to the first discharge capacity of the coin cell .
  • set [M 1 *(1-n 1 )*A 1 +M 2 *(1-n 2 )*A 2 ]*x/[M 3 *(1-n 3 )*y in Formula 2 ] is ⁇ , and according to an embodiment of the present application, the range of ⁇ may be 0.64-1.05.
  • the voltage plateau of Mn in LMFP is around 4.15V (vs. Li)
  • the voltage plateau of ternary material H2-H3 phase transition is around 4.25V (vs. Li)
  • LMFP and three The voltage platform of the element material has a voltage synergistic effect, which can reduce the instability of the surface structure caused by the H2-H3 phase transition of the ternary material itself. Therefore, the ternary material in the positive electrode active material is not prone to H2
  • the -H3 phase transition is beneficial to the structural stability of the ternary material and improves the safety performance and cycle performance of the ternary material.
  • the cathode active material obtained by mixing the LMFP and the ternary material avoids the double voltage platform of the cathode active material, which is beneficial to the full utilization of the capacity of each material in the cathode active material.
  • LMFP has higher safety performance than ternary materials, which can improve the safety of lithium-ion batteries.
  • the active lithium originating from the positive electrode active material needs to be consumed when the SEI film is formed on the surface of the negative electrode sheet.
  • the negative electrode is graphite
  • the initial efficiency of graphite is lower than that of LMFP material
  • the amount of irreversible lithium caused by the first effect problem of LMFP material is less, which is not enough for graphite to form SEI film, so that the graphite will additionally consume the active lithium in the LMFP, which reduces the actual specific capacity of the LMFP, resulting in low energy density of the lithium-ion battery
  • the first efficiency of the ternary material is smaller than that of the graphite, and the ternary material remains More irreversible lithium in the negative electrode is enough for graphite to form SEI film.
  • the ternary material is equivalent to supplementing lithium to LMFP in disguised form, which improves the actual specific
  • the ratio of the capacity provided by the negative electrode sheet to the capacity provided by the positive electrode sheet in the battery is called N/P (negative electrode active material gram capacity ⁇ negative electrode surface density ⁇ negative electrode active material content ratio) /(gram capacity of positive active material ⁇ positive surface density ⁇ positive active material content ratio) ratio
  • the range of this ratio is generally 1.08-1.12, that is, to reach the ratio range shown in formula 1.
  • the first efficiency of ternary materials is lower than that of graphite
  • the first efficiency of graphite is lower than that of LMFP
  • the mixing ratio of the two needs to be within a certain range.
  • the first efficiency of the mixed positive electrode active material and the first efficiency of the graphite material can be balanced, that is, to reach the ratio range shown in formula 2, satisfying the formula 2, which is conducive to improving the LMFP in the positive electrode active material.
  • the actual specific capacity of the material is exerted, and the energy density of the lithium-ion battery is improved on the basis of ensuring the safety of the lithium-ion battery.
  • the specific capacity of the LMFP in the positive electrode sheet of the lithium ion battery in the full battery is greater than 138mAh/g, and the specific capacity is the actual capacity of the LMFP material during the charging and discharging process of the lithium ion battery, Generally less than the theoretical specific capacity of the LMFP material.
  • the mass fraction of LMFP in the positive electrode active material ranges from 75% to 95%.
  • the ratio range shown in Formula 2 is satisfied, and the specific capacity of the LMFP in the positive electrode sheet of the lithium ion battery plays an important role in the whole battery. It can reach a level of 138mAh/g or even higher, which ensures the specific capacity of the LMFP material in the positive electrode active material.
  • the lithium ion battery further includes an electrolyte, and the lithium ion battery satisfies the following formula:
  • the Mn dissolution amount of the lithium ion battery at 45° C. and 2000 charge-discharge cycles is less than 700 ppm.
  • the residual alkali content on the surface of the ternary material is in the range of 500ppm-1500ppm
  • the liquid injection coefficient of the electrolyte is in the range of 2.9g/Ah-3.8g/Ah
  • the residual H 2 O content in the electrolyte is in the range of 200ppm-400ppm
  • the HF generated by the reaction of H 2 O with lithium hexafluorophosphate in the electrolyte can react with the residual alkali on the surface of the ternary material to achieve the consumption of HF and ensure the cycle performance of the positive active material and the life of the lithium ion battery.
  • the general formula of the ternary material is LiNi a1 Co b1 X c1 O 2 ;
  • the X is at least one metal element in the III subgroup to the V main group.
  • the mole fraction of Ni in the ternary material ranges from 80% to 95%.
  • the ternary material when the mole fraction of Ni in the ternary material ranges from 80% to 95%, the ternary material is called a high-nickel ternary material, and the high-nickel ternary material has the advantages of low cost, high energy density The advantages of high reversible capacity, high reversible capacity, and environmental friendliness can greatly improve the specific capacity of lithium-ion batteries.
  • the safety performance of high-nickel ternary materials is poor, when LMFP is mixed with high-nickel ternary materials, when the mixing ratio is within a certain range, the original safety performance of the LMFP material system can be guaranteed and the battery can be used safely.
  • Graphite was chosen with a first discharge capacity of 355 mAh/g and a first efficiency of 95%.
  • the injection coefficient of the electrolyte in the lithium ion battery is 3.1 g/Ah, and the residual H 2 O content in the electrolyte after the lithium ion battery is assembled is 200 ppm.
  • the separator PE double-sided coated ceramic separator
  • the electrolyte includes a solvent and LiPF 6
  • the solvent includes Ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC), and ethylene carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC)
  • EC Ethylene carbonate
  • DMC dimethyl carbonate
  • EMC methyl ethyl carbonate
  • EMC ethylene carbonate
  • EMC dimethyl carbonate
  • EMC ethylene carbonate
  • the lithium ion batteries of the following Examples 1 to 5 and Comparative Example 1 and Comparative Example 2 were obtained.
  • the mass fraction A 1 of LMFP in the positive electrode active material is 95%, and the mass fraction A 2 of the high nickel ternary material in the positive electrode active material is 5%.
  • the mass fraction A 1 of LMFP in the positive electrode active material is 88%, and the mass fraction A 2 of the high-nickel ternary material in the positive electrode active material is 12%.
  • the mass fraction A 1 of LMFP in the positive electrode active material was 85.5%, and the mass fraction A 2 of the high-nickel ternary material in the positive electrode active material was 14.5%.
  • the mass fraction A 1 of LMFP in the positive electrode active material is 75%, and the mass fraction A 2 of the high nickel ternary material in the positive electrode active material is 25%.
  • the mass fraction A 1 of LMFP in the positive electrode active material is 98%, and the mass fraction A 2 of the high nickel ternary material in the positive electrode active material is 2%.
  • the mass fraction A 1 of LMFP in the positive electrode active material is 70%, and the mass fraction A 2 of the high nickel ternary material in the positive electrode active material is 30%.
  • the above examples 1 to 5 and The lithium ion batteries of Comparative Example 1 and Comparative Example 2 were checked by formula 2 and formula 3 to obtain the values of ⁇ and ⁇ ; and the lithium ion batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were positive Specific capacity test of medium LMFP, capacity retention test after 2000 cycles at 45°C, Mn dissolution test after 2000 cycles at 45°C, and DSC (differential scanning calorimeter) thermal runaway trigger temperature of positive active material Test, the test process is as follows:
  • the above lithium-ion battery was charged at a rate of 0.1C and discharged at a rate of 0.1C.
  • the charge-discharge voltage range was 2.5V-4.2V, and the charge-discharge cycle was three times.
  • the above lithium-ion battery was charged at a rate of 1C, discharged at a rate of 1C, and the charge-discharge voltage range was 2.5V-4.2V. After 2000 cycles of charge and discharge at 45°C, according to the battery discharge capacity of the first cycle and the 2000th cycle The ratio of , to obtain the capacity retention rate of the battery after 2000 cycles;
  • the lithium-ion battery after 2000 cycles of charge and discharge at 45°C was disassembled, the negative active material of the negative electrode sheet was taken out, and the amount of Mn dissolved in the negative electrode active material was tested by ICP.
  • the positive electrode active material of the above-mentioned lithium ion battery Charge the positive electrode active material of the above-mentioned lithium ion battery to a fully charged state (specifically: first charge with a 0.1C constant current to a cut-off voltage of 4.2V, and then charge with a 4.2V constant voltage, and the cut-off current is 0.05C), the full charge
  • the electrical positive electrode sheet and electrolyte were placed in a high-temperature dry pot, heated at a heating rate of 5 °C/min, and their thermograms were tested by differential scanning calorimeter (DSC) to observe the trigger temperature of thermal runaway of the positive electrode material. .
  • Table 1 shows the verification data and test data of Formula 2 and Formula 3 for the lithium-ion batteries of Examples 1 to 5 and Comparative Example 1 and Comparative Example 2.
  • ⁇ and ⁇ are both within the range defined by Formula 2 and Formula 3 of the present application, that is, 0.49 ⁇ ⁇ 1.15, 0.6 ⁇ 2.91.
  • the full specific capacity of LMFP in the positive electrode sheet of the lithium-ion battery is greater than 138mAh/g, and the lithium-ion battery of Example 5 can reach 141mAh/g; the capacity retention rate of the lithium-ion battery after 2000 charge-discharge cycles is greater than 70%, Example 2
  • the lithium ion battery of Example 3 can reach 80%; the Mn dissolution amount of the lithium ion battery after 2000 charge-discharge cycle tests is less than 700ppm, and the Mn dissolution amount of the lithium ion battery of Example 3 is only 600ppm after 2000 charge-discharge cycle tests.
  • the DSC trigger temperature of the positive electrode active materials for lithium-ion batteries in Examples 1 to 5 is higher than 243 °C, that is, within the range below 243 °C Safe operation, improving the safety of lithium-ion batteries.
  • both ⁇ and ⁇ are not within the range defined by Formula 2 and Formula 3 of the present application, that is, ⁇ is not within the range of 0.49 to 1.15. ⁇ is not in the range of 0.6 to 2.91.
  • the full electric specific capacity of LMFP in the positive electrode sheet of lithium-ion battery is less than 135mAh/g
  • the capacity retention rate of lithium-ion battery after 2000 charge-discharge cycles is less than 60%
  • the amount of Mn dissolved in lithium-ion battery after 2000 times of charge-discharge cycle test is greater than 1000ppm
  • the Mn dissolution amount of the lithium-ion battery of Comparative Example 1 even reached 1350ppm after 2000 charge-discharge cycle tests.
  • the positive electrode active material of the lithium-ion battery in Comparative Example 2 contains more high-nickel ternary materials, and the DSC trigger temperature of the positive electrode active material is only 235 °C, which limits the use of lithium-ion batteries at high temperatures.

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Abstract

提供了一种锂离子电池，包括正极片和负极片，所述正极片的正极活性材料包括磷酸锰铁锂和三元材料，所述负极片的负极活性材料为石墨，所述锂离子电池满足如下公式： 1.08≤(M 3*η 3*y)/[(M 1*η 1*A 1+M 2*η 2*A 2)*x]≤1.12 (1) 0.49≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.15 (2) 其中，M 1为所述磷酸锰铁锂的首次充电比容量，单位为mAh/g，η 1为所述磷酸锰铁锂的首次效率，A 1为正极活性材料中磷酸锰铁锂的质量百分比，M 2为所述三元材料的首次充电比容量，单位为mAh/g，η 2为所述三元材料的首次效率，A 2为正极活性材料中三元材料的质量百分比，M 3为所述石墨的首次放电比容量，单位为mAh/g，η 3为所述石墨的首次效率，x为所述正极活性材料的敷料量，y为所述负极活性材料的敷料量，x与y的单位相同。

Description

锂离子电池
优先权信息
本申请请求于2020年10月28日向中国国家知识产权局提交的、专利申请号为202011175816.X、申请名称为“锂离子电池”的中国专利申请的优先权，并且其全部内容通过引用结合在本公开中。
技术领域
本申请涉及动力设备技术领域，具体地，本申请涉及一种锂离子电池。
背景技术
随着能源环保意识的逐渐加强，近年来新能源汽车得到了长足的发展。其中，电动汽车是主要方向之一。而在电动汽车的动力电池中，锂离子电池占据了非常重要的地位，作为锂离子电池重要的组成部分，正极材料的选择直接影响锂离子电池的性能。磷酸锰铁锂(简称LMFP)正极材料因结构稳定性高、循环性能及安全性能好而成为锂离子电池的主流正极材料。
磷酸锰铁锂具有较高的理论比容量和首次效率，可以给锂离子电池提供较高的容量。但锂离子电池负极石墨活性物质在充放电过程中会形成SEI膜，SEI膜形成的过程中会消耗磷酸锰铁锂的活性锂，降低了磷酸锰铁锂的实际比容量，限制了锂离子电池中磷酸锰铁锂容量的发挥。
公开内容
本申请实施例提供一种锂离子电池，以解决传统锂离子电池比容量中磷酸锰铁锂容量难以有效发挥的问题。
为了解决上述问题，本申请实施例采用下述技术方案：
本申请实施例提供了一种锂离子电池，包括：
正极片和负极片，所述正极片的正极活性材料包括磷酸锰铁锂和三元材料，所述负极片的负极活性材料为石墨，所述锂离子电池满足如下公式：
1.08≤(M 3*η 3*y)/[(M 1*η 1*A 1+M 2*η 2*A 2)*x]≤1.12  (1)
0.49≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.15  (2)
其中，M 1为所述磷酸锰铁锂的首次充电比容量，单位为mAh/g，η 1为所述磷酸锰铁锂的首次效率，A 1为正极活性材料中磷酸锰铁锂的质量百分比，M 2为所述三元材料 的首次充电比容量，单位为mAh/g，η 2为所述三元材料的首次效率，A 2为正极活性材料中三元材料的质量百分比，M 3为所述石墨的首次放电比容量，单位为mAh/g，η 3为所述石墨的首次效率，x为所述正极活性材料的敷料量，y为所述负极活性材料的敷料量，x与y的单位相同。
根据本申请的一些实施例，所述锂离子电池的正极片中磷酸锰铁锂在全电池中的实际比容量大于138mAh/g。
根据本申请的一些实施例，所述锂离子电池满足如下公式：
0.64≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.05。
根据本申请的一些实施例，所述锂离子电池还包括电解液，所述锂离子电池满足如下公式：
0.6≤(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)≤2.91  (3)
其中，a为所述三元材料的残碱含量，b为所述锂离子电池的注液系数，c为所述电解液中残留H 2O含量，所述a的取值范围为500ppm-1500ppm，所述b的取值范围为2.9g/Ah-3.8g/Ah，所述c的取值范围为200ppm-400ppm。
根据本申请的一些实施例，所述锂离子电池在45℃、2000次充放电循环后的Mn溶出量小于700ppm。
根据本申请的一些实施例，所述锂离子电池满足如下公式：
0.75≤(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)≤1.48。
根据本申请的一些实施例，所述y与所述x的比值范围为0.52-0.58。
根据本申请的一些实施例，以所述正极活性材料的总质量为基准，所述A 1的取值范围为75％-95％。
根据本申请的一些实施例，所述三元材料的通式为LiNi a1Co b1X c1O 2；
其中，0≤a1≤1，0≤b1≤1，0≤c1≤1，且a1+b1+c1＝1，所述X为第III副族至第V主族中的至少一种金属元素。
根据本申请的一些实施例，以所述三元材料中Ni、Co和X的摩尔数之和为基准，所述三元材料中Ni的摩尔数占比范围为80％-95％。
本申请实施例采用的技术方案能够达到以下有益效果：
本申请实施例提供的锂离子电池中正极片上的正极活性材料将三元材料和磷酸锰铁锂材料混用，并且使得磷酸锰铁锂和三元材料以及负极活性材料石墨满足上述式(1)和式(2)中的关系式，从而使得混用后的正极活性材料的首次效率和石墨材料的首次效率达到平衡，保证了磷酸锰铁锂的容量可以得到有效发挥，进而在保证锂离子电池高安全性的基础上，提升了锂离子电池的能量密度和循环性能。
本公开的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本公开的实践了解到。
附图说明
此处所说明的附图用来提供对本申请的进一步理解，构成本申请的一部分，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。在附图中：
图1为三元材料、LFMP和三元材料与LFMP混合材料的循环伏安(CV)曲线；
图2为三元材料、LFMP和三元材料与LFMP混合材料的首次充放电循环曲线。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合本申请具体实施例及相应的附图对本申请技术方案进行清楚、完整地描述。显然，所描述的实施例仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请的说明书和权利要求书中的术语“第一”、“第二”等是用于区别类似的对象，而不用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便本申请的实施例能够以除了在这里图示或描述的那些以外的顺序实施，且“第一”、“第二”等所区分的对象通常为一类，并不限定对象的个数，例如第一对象可以是一个，也可以是多个。此外，说明书以及权利要求中“和/或”表示所连接对象的至少其中之一，字符“/”，一般表示前后关联对象是一种“或”的关系。
以下结合附图，详细说明本申请各个实施例公开的技术方案。
本申请实施例提供了一种锂离子电池，包括：
正极片和负极片，所述正极片的正极活性材料包括LMFP(磷酸锰铁锂)和三元材料，所述负极片的负极活性材料为石墨，所述锂离子电池满足如下公式：
1.08≤(M 3*η 3*y)/[(M 1*η 1*A 1+M 2*η 2*A 2)*x]≤1.12  (1)
0.49≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.15  (2)
其中，M 1为所述LMFP的首次充电比容量，单位为mAh/g，η 1为所述LMFP的首次效率，A 1为正极活性材料中LMFP的质量百分比，M 2为所述三元材料的首次充电比容量，单位为mAh/g，η 2为所述三元材料的首次效率，A 2为正极活性材料中三元材料的质量百分比，M 3为所述石墨的首次放电比容量，单位为mAh/g，η 3为所述石墨的首次效率，x为所述正极活性材料的敷料量，y为所述负极活性材料的敷料量，x与y的单位相同，y与x的比值范围为0.52-0.58。
具体地，对于正极活性材料来讲，首次效率为扣式电池的首次放电容量和首次充电容量的比值；对于负极活性材料来讲，首次效率为扣式电池的首次充电容量和首次放电容量的比值。
进一步地，设定公式2中[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]为α，根据本申请的一个实施例，α的范围可以为0.64-1.05。
具体地，参见图1和图2，LMFP中Mn的电压平台在4.15V(vs.Li)左右，三元材料H2-H3相变的电压平台在4.25V(vs.Li)左右，LMFP和三元材料的电压平台存在电压协同效应，这种协同效应可以降低由于三元材料自身H2-H3相变所带来的表面结构不稳定性，因此，所述正极活性材料中三元材料不易发生H2-H3相变，有利于三元材料的结构稳定，提高三元材料的安全性能和循环性能。所以，LMFP和三元材料混合得到的正极活性材料避免了正极活性材料出现双电压平台，从而有利于正极活性材料中各材料的容量充分发挥。而且LMFP相对于三元材料具有较高的安全性能，可以提高锂离子电池的安全性。
锂离子电池在首次充放电过程中，负极片表面形成SEI膜时需要消耗来源于正极活性材料中的活性锂。当负极为石墨，由于石墨的首次效率小于LMFP材料的首次效率，在只采用LMFP材料作为正极活性材料时，LMFP材料因首效问题造成的不可逆锂量较少，不足以给石墨用来形成SEI膜，使得石墨会额外消耗LMFP中的活性锂，这就降低了LMFP的实际比容量发挥，进而造成锂离子电池能量密度低；而三元材料的首次效率小于石墨的首次效率，三元材料留在负极中的较多不可逆锂足够石墨形成SEI膜，当LMFP和三元材料混用时，三元材料相当于变相给LMFP补锂，提高了LMFP在全电池中的实际比容量，提高了锂离子电池的能量密度。
而在锂离子电池设计时，电池中由负极片所提供的容量与由正极片所提供的容量的比值称之为N/P(负极活性物质克容量×负极面密度×负极活性物含量比)/(正极活性物质克容量×正极面密度×正极活性物含量比)比，该比值的范围一般在1.08-1.12，也就是要达到公式1所示的比例范围。更重要的是，因为三元材料的首次效率低于石墨的首次效率，而石墨的首次效率又低于LMFP的首次效率，当三元材料和LMFP材料混用时，二者的混用比例需要在一定范围内，才可以使混用后的正极活性材料的首次效率和石墨材料的首次效率达到平衡，也就是要达到公式2所示的比例范围，满足所述公式2，有利于提升正极活性材料中LMFP材料的实际比容量发挥，在保证了锂离子电池的安全性的基础上，提高了锂离子电池的能量密度。
根据本申请的再一个实施例，所述锂离子电池正极片中LMFP在全电池中的比容量大于138mAh/g，该比容量是LMFP材料在锂离子电池充放电过程中实际发挥出的容 量，一般小于LMFP材料的理论比容量。以所述正极活性材料的总质量为基准，所述正极活性材料中LMFP的质量分数范围为75％-95％。
具体地，在三元材料和LMFP材料混用的情况下，当三元材料的比例过低时，三元材料由于首次效率低造成损失的锂离子也就过低，这些锂离子不足以给石墨用来消耗并形成SEI膜，也就需要额外消耗LMFP中的锂离子来用于负极片中石墨的SEI膜的形成，这便会导致正极片中LMFP的实际比容量偏低；当正极活性材料中三元材料的比例过高时，一方面由于三元材料结构稳定性相对于LMFP较差，会导致正极活性材料混合体系的循环容量保持率偏低，另一方面三元材料在充放电过程中安全性能较低，不利于锂离子电池的安全使用。所以锂离子电池在混用正极活性材料的首次效率和石墨材料的首次效率达到平衡时，也就是满足公式2所示的比例范围，所述锂离子电池正极片中LMFP在全电池中的比容量发挥可以达到138mAh/g，甚至更高的水平，保证了正极活性材料中LMFP材料的比容量发挥。
根据本申请的又一个实施例，所述锂离子电池还包括电解液，所述锂离子电池满足如下公式：
0.6≤(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)≤2.91  (3)
其中，a为所述三元材料的残碱含量，单位为ppm，b为所述锂离子电池的注液系数，单位为g/Ah，c为所述电解液中残留H 2O含量，单位为ppm。
进一步地，设定公式3中(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)的值为β，根据本申请的一个实施例，β的取值范围可以为0.75-1.48。
具体地，在电池的实际配制过程中，电解液中会不可避免地存在一定量的痕量水，由于H 2O与电解液中的六氟磷酸锂等锂盐反应易生成HF(氢氟酸)，HF会导致LMFP中的Fe和Mn溶出，降低了LMFP材料的结构稳定性和锂离子电池的循环寿命。而三元材料表面的残碱会和电解液中产生的HF反应，即HF会被消耗，从而有助于抑制LMFP材料中Fe和Mn的溶出，而且对Mn溶出的抑制更加明显，进而有利于提高正极活性材料的循环性能，有助于提升锂离子电池的寿命。所以三元材料的残碱含量、锂离子电池中电解液的注液系数以及电解液中残留H 2O含量需要满足公式3所示的比例范围，以达到充分利用三元材料表面的残碱对电解液中HF的有效消耗，提升锂离子电池的寿命。
根据本申请的又一个实施例，所述锂离子电池在45℃、2000次充放电循环后的Mn溶出量小于700ppm。
具体地，在锂离子电池充放电过程中，当电解液中存在较多的HF时，LMFP材料中Fe和Mn的溶出量较高，破坏了LMFP材料的结构完整性，降低了LMFP材料的 循环、倍率等电性能。而利用三元材料表面的残碱对电解液中HF进行有效消耗后，可以大大降低LMFP材料中Fe和Mn的溶出，特别是降低对Mn的溶出，使得锂离子电池在45℃、2000次充放电循环后的Mn溶出量仍然可以小于700ppm，提升了电池的循环性能。
根据本申请的又一个实施例，所述a的取值范围为500ppm-1500ppm，所述b的取值范围为2.9g/Ah-3.8g/Ah，所述c的取值范围为200ppm-400ppm。
具体地，也就是三元材料表面的残碱含量范围在500ppm-1500ppm，电解液的注液系数范围为2.9g/Ah-3.8g/Ah，电解液中残留H 2O含量范围为200ppm-400ppm，H 2O与电解液中的六氟磷酸锂反应生成的HF可以与三元材料表面的残碱反应，达到对HF的消耗，保证了正极活性材料的循环性能和锂离子电池的寿命。
根据本申请的又一个实施例，所述三元材料的通式为LiNi a1Co b1X c1O 2；
其中，0≤a1≤1，0≤b1≤1，0≤c1≤1，且a1+b1+c1＝1，所述X为第III副族至第V主族中的至少一种金属元素。
具体地，三元材料中的Mn元素可以部分或者全部被Al、Zr、Ti、Y、Sr和W等元素替代，以提高所述三元材料的安全稳定性和晶体结构的完整性。
根据本申请的一个具体实施例，以所述三元材料中Ni、Co和X的摩尔数之和为基准，所述三元材料中Ni的摩尔数分数范围为80％-95％。
具体地，所述三元材料中Ni的摩尔数分数范围为80％-95％的情况下，所述三元材料被称为高镍三元材料，高镍三元材料具有成本低、能量密度高、可逆容量高和环境友好等优点，可以大大提高锂离子电池的比容量。虽然高镍三元材料的安全性能较差，但LMFP与高镍三元材料混合使用时，当混合比例在一定范围时，可以保证LMFP材料体系的原有安全性能，保证电池的使用安全。
下面以具体实施例的形式对本申请的技术方案进行详细说明：
正极活性材料的选取：
选取首次充电比容量为165mAh/g和首次效率为98％的LMFP，选取首次充电比容量为238mAh/g和首次效率为86％的高镍三元材料(Ni、Co和Mn的摩尔比为0.83:0.12:0.05)，将LMFP和高镍三元材料混合形成正极活性材料，正极活性材料中LMFP的质量分数为A 1，正极活性材料中高镍三元材料的质量分数为A 2，其中，A 1+A 2＝1。其中，高镍三元材料的残碱含量为700ppm。
负极活性材料的选取：
选择首次放电容量为355mAh/g和首次效率为95％的石墨。
电解液的选取：
锂离子电池中电解液的注液系数为3.1g/Ah，锂离子电池装配后电解液中残留H 2O含量为200ppm。
按照上述选取的正极活性材料、负极活性材料和电解液制备锂离子电池，制备流程包括：
S101，将NMP(N-甲基吡咯烷酮)和PVDF(聚偏氟乙烯)加入到搅拌机中搅拌1h，然后加入导电石墨作为导电剂搅拌0.5h，再加入正极活性材料(磷酸锰铁锂和三元材料)搅拌1.5h形成正极浆料，将正极浆料过筛后涂布在铝箔集流体上，将涂布有正极浆料的铝箔在80℃下真空干燥12h，最后辊压和分切干燥后涂布有正极浆料的铝箔得到正极片。正极片的单面面密度为2.0g/dm 2，正极片的压实密度为2.6g/cm 3；
S102，将水、SBR与CMC混合(SBR为丁苯橡胶，CMC为羧甲基纤维素钠)后加入到搅拌机中搅拌1h，然后加入导电石墨作为导电剂搅拌0.5h，再加入负极活性材料石墨搅拌1.5h形成负极浆料，将负极浆料过筛后涂布在铜箔集流体上，将涂布有负极浆料的铜箔在100℃下真空干燥12h，最后辊压和分切干燥后涂布有负极浆料的铜箔得到负极片；
S103，将正极片、隔膜和负极片放入电池壳体内，隔膜(PE双面涂陶瓷隔膜)位于正极片和负极片之间，然后注入电解液(电解液包括溶剂和LiPF 6，其中溶剂包括碳酸乙烯酯(EC)、碳酸二甲酯(DMC)和碳酸甲基乙基酯(EMC)，并且碳酸乙烯酯(EC)、碳酸二甲酯(DMC)和碳酸甲基乙基酯(EMC)体积比为1:1:1，电解液中LiPF 6的浓度为1mol/L)后密封电池壳体，得到锂离子电池。
具体得到如下实施例1至实施例5和对比例1以及对比例2的锂离子电池。
实施例1
正极活性材料中LMFP的质量分数A 1为95％，正极活性材料中高镍三元材料的质量分数A 2为5％。
实施例2
正极活性材料中LMFP的质量分数A 1为91.1％，正极活性材料中高镍三元材料的质量分数A 2为8.9％。
实施例3
正极活性材料中LMFP的质量分数A 1为88％，正极活性材料中高镍三元材料的质量分数A 2为12％。
实施例4
正极活性材料中LMFP的质量分数A 1为85.5％，正极活性材料中高镍三元材料的质量分数A 2为14.5％。
实施例5
正极活性材料中LMFP的质量分数A 1为75％，正极活性材料中高镍三元材料的质量分数A 2为25％。
对比例1
正极活性材料中LMFP的质量分数A 1为98％，正极活性材料中高镍三元材料的质量分数A 2为2％。
对比例2
正极活性材料中LMFP的质量分数A 1为70％，正极活性材料中高镍三元材料的质量分数A 2为30％。
在控制石墨在负极片上的敷料量y，与正极活性材料在正极片上的敷料量x(x与y单位相同)的比值y/x＝0.55的基础上，对上述实施例1至实施例5和对比例1以及对比例2的锂离子电池进行公式2和公式3的验算，获得α和β的数值；并对实施例1至实施例5和对比例1以及对比例2的锂离子电池进行正极中LMFP的比容量测试、在45℃下循环2000次后容量保持率测试、在45℃下循环2000次后Mn溶出量的测试以及正极活性材料DSC(差示扫描量热仪)热失控触发温度测试，测试过程具体为：
正极中LMFP的全电比容量测试：
在常温(25℃)下，将上述锂离子电池以0.1C倍率充电，0.1C倍率放电，充放电电压范围为2.5V-4.2V，充放电循环三次，根据极片的敷料量和锂离子电池的第三次放电容量来计算正极中LMFP的全电比容量；
2000次充放电循环后容量保持率测试：
将上述锂离子电池以1C倍率充电，1C倍率放电，充放电电压范围为2.5V-4.2V，在45℃充放电2000个循环后，根据电池第一个循环和第2000个循环的电池放电容量的比值，得出电池2000个循环后的容量保持率；
2000次充放电循环后Mn溶出量测试：
将45℃充放电2000个循环后的锂离子电池拆解，取出负极片的负极活性材料，利用ICP测试负极活性材料中Mn的溶出量。
正极活性材料DSC热失控触发温度测试：
将上述锂离子电池的正极活性材料充电至满电态(具体方式为：先以0.1C恒流充电至截止电压为4.2V，再以4.2V恒压充电，截止电流是0.05C)，将满电态的正极片和电解液置于高温干锅中，以5℃/min的升温速率升温，通过差示扫描量热仪(DSC)测试其热谱图，以观察正极材料热失控的触发温度。
表1给出了实施例1至实施例5和对比例1以及对比例2的锂离子电池进行公式2 和公式3的验算数据及测试数据。
表1各例证中锂离子电池验算和测试数据
Figure PCTCN2021126905-appb-000001
备注：表1中2000次充放电循环测试后Mn溶出量为折算成纯LMFP对应的Mn溶出量。
从表1中可以看出，实施例1至实施例5的锂离子电池在进行公式2和公式3验算后，α和β均在本申请公式2和公式3限定的范围内，也就是0.49≤α≤1.15，0.6≤β≤2.91。而且锂离子电池正极片中LMFP的全电比容量大于138mAh/g，实施例5的锂离子电池可以达到141mAh/g；锂离子电池2000次充放电循环后容量保持率大于70％，实施例2的锂离子电池可以达到80％；锂离子电池2000次充放电循环测试后Mn溶出量小于700ppm，实施例3的锂离子电池2000次充放电循环测试后Mn溶出量仅有600ppm。在安全性方面，由于LMFP和高镍三元材料的有效配合，使得实施例1至实施例5的锂离子电池正极活性材料DSC触发温度高于243℃，也就是可以在243℃以下的范围内安全运行，提高了锂离子电池的安全性。
而对比例1和对比例2的锂离子电池在进行公式2和公式3验算后，α和β均不在本申请公式2和公式3限定的范围内，也就是α不在0.49至1.15的范围内，β不在0.6至2.91的范围内。而且锂离子电池正极片中LMFP的全电比容量均小于135mAh/g，锂离子电池2000次充放电循环后容量保持率小于60％，锂离子电池2000次充放电循环测试后Mn溶出量大于1000ppm，对比例1的锂离子电池2000次充放电循环测试后Mn溶出量甚至达到了1350ppm。在安全性方面，对比例2的锂离子电池正极活性材料中 由于含有较多的高镍三元材料，正极活性材料DSC触发温度仅为235℃，限制了锂离子电池在高温下的使用。
上面结合附图对本申请的实施例进行了描述，但是本申请并不局限于上述的具体实施方式，上述的具体实施方式仅仅是示意性的，而不是限制性的，本领域的普通技术人员在本申请的启示下，在不脱离本申请宗旨和权利要求所保护的范围情况下，还可做出很多形式，均属于本申请的保护之内。

Claims (10)

  1. 一种锂离子电池，其中，包括：
    正极片和负极片，所述正极片包括正极活性材料，所述正极活性材料包括磷酸锰铁锂和三元材料，所述负极片包括负极活性材料，所述负极活性材料为石墨，所述锂离子电池满足如下公式：
    1.08≤(M 3*η 3*y)/[(M 1*η 1*A 1+M 2*η 2*A 2)*x]≤1.12  (1)
    0.49≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.15  (2)
    其中，M 1为所述磷酸锰铁锂的首次充电比容量，单位为mAh/g，η 1为所述磷酸锰铁锂的首次效率，A 1为所述磷酸锰铁锂在所述正极活性材料中的质量百分比，M 2为所述三元材料的首次充电比容量，单位为mAh/g，η 2为所述三元材料的首次效率，A 2为所述三元材料在所述正极活性材料中的质量百分比，M 3为所述石墨的首次放电比容量，单位为mAh/g，η 3为所述石墨的首次效率，x为所述正极活性材料的敷料量，y为所述负极活性材料的敷料量，x与y的单位相同。
  2. 根据权利要求1所述的锂离子电池，其中，所述锂离子电池的正极片中所述磷酸锰铁锂在全电池中的实际比容量大于138mAh/g。
  3. 根据权利要求1或2所述的锂离子电池，其中，所述锂离子电池满足如下公式：
    0.64≤[M 1*(1-η 1)*A 1+M 2*(1-η 2)*A 2]*x/[M 3*(1-η 3)*y]≤1.05。
  4. 根据权利要求1-3中任一项所述的锂离子电池，其中，还包括电解液，所述锂离子电池满足如下公式：
    0.6≤(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)≤2.91  (3)
    其中，a为所述三元材料的残碱含量，b为所述锂离子电池的注液系数，c为所述电解液中残留H 2O含量，所述a的取值范围为500ppm-1500ppm，所述b的取值范围为2.9g/Ah-3.8g/Ah，所述c的取值范围为200ppm-400ppm。
  5. 根据权利要求1-4中任一项所述的锂离子电池，其中，所述锂离子电池在45℃、2000次充放电循环后的Mn溶出量小于700ppm。
  6. 根据权利要求1-5中任一项所述的锂离子电池，其中，所述锂离子电池满足如下公式：
    0.75≤(M 1*η 1*A 1+M 2*η 2*A 2)*b*c/(a*A 2*1000)≤1.48。
  7. 根据权利要求1-6中任一项所述的锂离子电池，其中，所述y与所述x的比值范围为0.52-0.58。
  8. 根据权利要求1-7中任一项所述的锂离子电池，其中，以所述正极活性材料的 总质量为基准，所述A 1的取值范围为75％-95％。
  9. 根据权利要求1-8中任一项所述的锂离子电池，其中，所述三元材料的通式为LiNi a1Co b1X c1O 2；
    其中，0≤a1≤1，0≤b1≤1，0≤c1≤1，且a1+b1+c1＝1，所述X为第III副族至第V主族中的至少一种金属元素。
  10. 根据权利要求1-9中任一项所述的锂离子电池，其中，以所述三元材料中Ni、Co和X的摩尔数之和为基准，所述三元材料中Ni的摩尔数占比范围为80％-95％。
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