Electrochemical device and electric device

Abstract

The invention provides an electrochemical device and a power utilization device, and belongs to the technical field of secondary batteries, the electrochemical device comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive active material layer arranged on the positive current collector, and the positive active material layer comprises a positive material; a positive electrode material comprises lithium manganese iron phosphate and nickel cobalt lithium manganate, and the positive electrode material meets the relation of a formula I: # imgabs0 #. According to the electrochemical device, the lithium manganese iron phosphate and the nickel cobalt lithium manganate are introduced into the positive electrode material at the same time, and by adjusting the particle size, the mixing proportion and the discharge capacity under high potential of the lithium manganese iron phosphate and the nickel cobalt lithium manganate, the electrochemical performance of the device is improved; therefore, the nickel cobalt lithium manganate material can share the charge and discharge current in the electric quantity interval corresponding to the Mn charge and discharge voltage platform in the lithium manganese iron phosphate, and the cycle performance of the electrochemical device is effectively optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to an electrochemical device and an electrical device. Background Art

[0002] With the widespread application of electronic products and the popularity of electric vehicles, people have put forward higher requirements on batteries. Energy density is a key indicator to determine battery life.

[0003] In order to meet the increasing demand for energy density in the field of new energy vehicles, lithium manganese iron phosphate materials, which have the same advantages as lithium iron phosphate, such as safety and low cost, have attracted much attention. The voltage platform of lithium manganese iron phosphate materials is about 4.1V, the energy density is close to that of the five-series ternary materials, and the low-temperature performance is better than that of lithium iron phosphate materials. It can be used as an optional positive electrode material to further improve the energy density of lithium-ion batteries.

[0004] Lithium iron manganese phosphate material has a dual potential platform during the charge and discharge process. Lithium iron manganese phosphate material is affected by Mn doping, and its lithium ion diffusion rate in the high potential Mn platform is one order of magnitude lower than that in the low potential Fe platform. This makes the charge and discharge efficiency of lithium iron manganese phosphate material too low at the high potential platform, and it is easy to suffer structural damage at high rate current, thereby deteriorating the cycle performance of the electrochemical device.

[0005] Therefore, it is necessary to design an electrochemical device and an electrical device to improve the above problems. Summary of the invention

[0006] In view of the above shortcomings of the prior art, the present invention provides an electrochemical device and an electrical device to improve the technical problem that the introduction of lithium iron manganese phosphate material into the positive electrode material of the existing electrochemical device easily deteriorates the cycle performance of the electrochemical device.

[0007] To achieve the above-mentioned object and other related objects, the present invention provides an electrochemical device, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising a positive electrode material; the positive electrode material comprises lithium manganese iron phosphate and lithium nickel cobalt manganese oxide; the positive electrode material satisfies the relationship of formula I:

[0008]

[0009] Among them, A is the mass proportion of the lithium manganese iron phosphate in the lithium manganese iron phosphate and the nickel cobalt manganese oxide, and 0.6≤A≤0.8; D1 is the median particle size Dv50 of the lithium manganese iron phosphate, and D2 is the median particle size Dv50 of the nickel cobalt manganese oxide; Q1 is the gram capacity of the lithium manganese iron phosphate when the potential of the electrochemical device is higher than 3.95V, 80mAh / g≤Q1≤92mAh / g; Q2 is the gram capacity of the nickel cobalt manganese oxide when the potential of the electrochemical device is higher than 3.95V, Q2≥80mAh / g.

[0010] In an example of the present invention, D1 is greater than or equal to 0.59 μm, and D2 is less than or equal to 3.5 μm.

[0011] In one example of the present invention, the lithium manganese iron phosphate is a secondary particle, and the median particle size Dv50 of the primary particles contained in the secondary particles is 0.1-0.3 μm.

[0012] In one example of the present invention, the lithium manganese iron phosphate is LiMn x Fe (1-x) PO4, where 0.6≤x≤0.8.

[0013] In an example of the present invention, the lithium manganese iron phosphate is doped with a first doping element, and the first doping element includes at least one of K, Na, Cu, Zn and Ni.

[0014] In one example of the present invention, the lithium nickel cobalt manganese oxide is LiNi a Co b Mn c O2, where a+b+c=1, a≥0.6.

[0015] In one example of the present invention, the lithium nickel cobalt manganese oxide LiNi a Co b Mn c In O2, 0.8≤a≤0.88.

[0016] In an example of the present invention, the lithium nickel cobalt manganese oxide is doped with a second doping element, and the second doping element includes at least one of Fe, Na, and Ca.

[0017] In an example of the present invention, the thickness of the positive electrode active material layer located on any one side of the positive electrode current collector is 40-100 μm.

[0018] In one example of the present invention, the compaction density of the positive electrode active material layer is 3 to 3.2 g / cm 3 .

[0019] In one example of the present invention, the electrochemical device further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode collector and a negative electrode active material layer disposed on the negative electrode collector, and the thickness of the negative electrode active material layer located on any one side of the negative electrode collector is 50 to 100 μm.

[0020] In one example of the present invention, the compaction density of the negative electrode active material layer is 1.45-1.8 g / cm 3 .

[0021] The present invention further provides an electrical device, comprising the secondary battery described in any one of the above examples.

[0022] The present invention provides an electrochemical device. The electrochemical device simultaneously introduces lithium manganese iron phosphate and lithium nickel cobalt manganese oxide into a positive electrode material, and by adjusting the particle size, mixing ratio and discharge capacity of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide at a high potential, the lithium nickel cobalt manganese oxide material can achieve the effect of sharing the charge and discharge current in the electric quantity interval corresponding to the Mn charge and discharge voltage platform in the lithium manganese iron phosphate, thereby improving the rate performance of the electrochemical device in the high potential platform stage and optimizing the cycle performance of the electrochemical device. DETAILED DESCRIPTION

[0023] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the features in the following embodiments and the embodiments can be combined with each other without conflict. It should also be understood that the terms used in the embodiments of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturers.

[0024] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" etc. used in this specification are only for the convenience of description and are not intended to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be regarded as the scope of implementation of the present invention.

[0025] In this specification, the average particle size (Dv50) may be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve of the particles. Dv50 may be measured, for example, by a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes ranging from the submicron range to several millimeters, thereby obtaining results with high reproducibility and high resolution.

[0026] The present invention provides an electrochemical device. By adjusting the particle sizes, mixing ratios and discharge capacities of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide at high potentials in positive electrode materials, the electrochemical device enables the charging and discharging processes of lithium nickel cobalt manganese oxide at high potentials above 3.95 V to highly overlap with the lithium deintercalation process of Mn ions in lithium iron manganese phosphate in terms of time, thereby ensuring that the lithium nickel cobalt manganese oxide material performs effective current shunting in the electric quantity interval corresponding to the Mn charging and discharging voltage platform in the lithium iron manganese phosphate, thereby improving the charging and discharging efficiency of the electrochemical device at high potentials, making full use of the capacity of lithium iron manganese phosphate at high potentials, and optimizing the rate and cycle performance of the electrochemical device.

[0027] The present invention provides an electrochemical device in one aspect, and a specific embodiment of the electrochemical device is a battery including one or more "battery cells". The "battery cell" refers to a battery cell that can be charged and discharged independently. The "battery cell" includes a positive electrode plate, a negative electrode plate, an electrolyte, a separator, and corresponding connecting accessories and circuits. The positive electrode plate includes a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector, and the positive electrode active material layer includes a positive electrode material, a positive electrode conductive agent, and a positive electrode binder; the negative electrode plate includes a negative electrode collector and a negative electrode active material layer disposed on the negative electrode collector, and the negative electrode active material layer includes a negative electrode material, a negative electrode conductive agent, a negative electrode binder, and a thickener. In the electrochemical device, the positive and negative electrode materials can deintercalate lithium ions to achieve energy storage and release, the electrolyte is a carrier for lithium ions to be transmitted between the positive electrode plate and the negative electrode plate, and the separator can pass lithium ions but is not conductive, thereby separating the positive electrode plate and the negative electrode plate to prevent short circuit. It should be noted that the type of negative electrode material used in the negative electrode plate can be any negative electrode active material known in the art. For example, the negative electrode material can be a carbon-based material (such as graphite, hard carbon or soft carbon), a silicon-based material (such as silicon oxide) or a carbon-silicon composite material.

[0028] In the electrochemical device, the positive electrode material includes lithium iron manganese phosphate and lithium nickel cobalt manganese oxide. The parameters of the positive electrode material satisfy the relationship shown in formula I:

[0029] S1≤S2(Formula I)

[0030]

[0031] S2=2.8344×(1-A)-1.188 (Formula III)

[0032] Wherein, A is the mass proportion of lithium iron manganese phosphate in lithium iron manganese phosphate and lithium nickel cobalt manganese oxide, and 0.6≤A≤0.8; D1 is the median particle size Dv50 of lithium iron manganese phosphate, and D2 is the median particle size Dv50 of lithium nickel cobalt manganese oxide; Q1 is the charge and discharge capacity in grams of lithium iron manganese phosphate when the potential of the electrochemical device is higher than 3.95V, 80mAh / g≤Q1≤92mAh / g; Q2 is the charge and discharge capacity in grams of lithium nickel cobalt manganese oxide when the potential of the electrochemical device is higher than 3.95V, Q2≥80mAh / g. It should be noted that the theoretical gram capacity of lithium iron manganese phosphate when the potential of the electrochemical device is higher than 3.95V is affected by its internal element composition, especially the Mn / Fe component ratio. For example, the higher the Mn element composition in lithium iron manganese phosphate, the higher the theoretical gram capacity above 3.95V. Similarly, the theoretical gram capacity of lithium nickel cobalt manganese oxide when the potential of the electrochemical device is higher than 3.95V is affected by its internal element composition, especially the Ni / Co / Mn component ratio. For example, the higher the Ni element composition in lithium nickel cobalt manganese oxide, the higher the theoretical gram capacity above 3.95V. The actual gram capacity Q1 of lithium iron manganese phosphate when the potential of the electrochemical device is higher than 3.95V and the actual gram capacity Q2 of lithium nickel cobalt manganese oxide when the potential of the electrochemical device is higher than 3.95V are affected by the material's own impedance on the basis of the theoretical gram capacity. If the material impedance is large, Q1 and Q2 will be greatly reduced on the basis of the theoretical gram capacity, and if the material impedance is small, Q1 and Q2 will be slightly reduced on the basis of the theoretical gram capacity. In addition, the Q1 capacity of lithium iron manganese phosphate and the Q2 capacity of lithium nickel cobalt manganese oxide may be affected by additional doping elements in addition to the above factors.

[0033] In the relationship shown in Formula I, the parameter S1 represents the ratio of the charge and discharge time of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide at a potential above 3.95V; wherein AQ1 represents the charge and discharge capacity of lithium manganese iron phosphate at a potential above 3.95V, (1-A)Q2 represents the charge and discharge capacity of lithium nickel cobalt manganese oxide at a potential above 3.95V, and since the particle size of the material is inversely proportional to the rate performance, It can represent the speed ratio of the capacity of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide being drained or filled above a potential of 3.95V. The S2 parameter represents the mean regression of the S1 parameter under different mass proportions of lithium iron manganese phosphate. Therefore, the relationship shown in Formula I indicates that the charge and discharge time of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide above a potential of 3.95V tends to be consistent. When the positive electrode material in the electrochemical device satisfies the relationship shown in Formula I, the charge and discharge process of lithium nickel cobalt manganese oxide above a potential of 3.95V can be accompanied by the charge and discharge process involving Mn ions in lithium iron manganese phosphate for a long time, so as to ensure that lithium nickel cobalt manganese oxide can effectively share the current in the charge interval corresponding to the Mn potential platform in lithium iron manganese phosphate, so that the capacity of the lithium iron manganese phosphate material under the Mn potential platform is stimulated by sufficient charge and discharge current and fully released.

[0034] In addition, in the relationship shown in Formula I, the test method for each physical parameter is as follows:

[0035] D1 parameter measurement method: disassemble the fully charged positive electrode plate in the electrochemical device, clean and dry it, cut a sample of about 5mm×5mm near the center area of ​​the plate, and enter the cross section polishing (CP). By screening out the characteristic element Fe, the lithium iron manganese phosphate particles are marked in the positive electrode material, and then the lithium iron manganese phosphate particles are statistically sampled for particle size statistics to obtain the median particle size of the lithium iron manganese phosphate particles.

[0036] D2 parameter measurement method: disassemble the fully charged positive electrode plate in the electrochemical device, clean and dry it, cut a sample of about 5mm×5mm near the center area of ​​the plate, and enter the cross section polishing (CP). By screening out the characteristic element Ni, the nickel cobalt manganese oxide particles are marked in the positive electrode material, and then the nickel cobalt manganese oxide particles are statistically sampled for particle size statistics to obtain the median particle size of the nickel cobalt manganese oxide particles.

[0037] The test method for the mass proportion A of lithium iron manganese phosphate and the manganese-iron ratio α is: disassemble the positive electrode plate in the electrochemical device, scrape a certain amount of positive electrode powder (>5g) from the positive electrode plate, perform ICP test on the positive electrode powder sample, and calculate the mass proportion A of lithium iron manganese phosphate in lithium iron manganese phosphate and lithium nickel cobalt manganese oxide, as well as the manganese-iron molar ratio α in lithium iron manganese phosphate.

[0038] Q1 and Q2 parameter measurement method: disassemble the fully charged positive electrode plate in the electrochemical device, cut off the plate sample, and assemble the plate sample into a button half-cell. By charging and discharging the button half-cell at a constant current rate of 0.1C / 0.1C in the test voltage range of 2 to 4.4V, the total reversible capacity Q of the positive electrode material can be tested. totalThen, through the dQ / dV and VQ curve tests, the charge and discharge capacity Q contributed by the Fe ion platform 3.4V in lithium manganese iron phosphate can be obtained. Fe , combined with the molar ratio of manganese to iron in lithium manganese iron phosphate, it is calculated that Q1 = Q Fe / α; and, through the dQ / dV and VQ curves, the charge and discharge capacity Q of the positive electrode material above 3.95V can be obtained. ≥3.95V , we can further calculate that Q2=Q ≥3.95V -Q1.

[0039] In some embodiments, lithium manganese iron phosphate is LiMn x Fe (1-x) PO4, wherein the Mn element component x satisfies 0.6≤x≤0.8, for example, the Mn element component x can be 0.6, 0.7 or 0.8, and correspondingly, the lithium manganese iron phosphate can be LiMn 0.6 Fe 0.4 PO4、LiMn 0.7 Fe 0.3 PO4 or LiMn 0.8 Fe 0.2 PO4.

[0040] In some embodiments, lithium nickel cobalt manganese oxide is LiNi a Co b Mn c O2, wherein 0.6≤a<1, 0.4<b<1, 0.4<c<1, a+b+c=1. For example, lithium nickel cobalt manganese oxide can be LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.7 Co 0.15 Mn 0.15 O2、LiNi 0.8 Co 0.1 Mn0.O2 or LiNi 0.9 Co 0.05 Mn 0.05 Optionally, in some embodiments, the Ni element component a in the nickel cobalt manganese oxide satisfies 0.8≤a≤0.88, and correspondingly, the nickel cobalt manganese oxide may be LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.82 Co 0.09 Mn 0.09 O2、LiNi 0.84 Co 0.08 Mn 0.08 O2、LiNi 0.86 Co 0.07 Mn 0.07O2 or LiNi 0.88 Co 0.06 Mn 0.06 O2.

[0041] In some embodiments, the median particle size D1 of lithium iron manganese phosphate is greater than or equal to 0.59 μm, for example, it can be 0.6 μm, 0.63 μm, 0.65 μm, 0.67 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm or 0.9 μm; the median particle size D2 of lithium nickel cobalt manganese oxide is less than or equal to 3.5 μm, for example, it can be 2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm or 3.5 μm. When the median particle size of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is within the above range, the particle size difference between lithium iron manganese phosphate and lithium nickel cobalt manganese oxide can be used to compensate for the rate performance difference between the two when charging and discharging at a potential above 3.95V, so that the charging and discharging speeds of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide at a potential above 3.95V are as close as possible, thereby ensuring the high-potential shunting effect of lithium cobalt manganese oxide, while providing space for increasing the content of lithium iron manganese phosphate in the positive electrode material and reducing the content of lithium nickel cobalt manganese oxide.

[0042] In some embodiments, lithium manganese iron phosphate is a secondary particle, and the median particle size Dv50 of the primary particles contained in the lithium manganese iron phosphate secondary particles is any value between 0.1 and 0.3 μm, for example, 0.1 μm, 0.12 μm, 0.15 μm, 0.17 μm, 0.2 μm, 0.22 μm, 0.25 μm, 0.27 μm or 0.3 μm. It should be noted that the particle size of the primary particles in the lithium manganese iron phosphate secondary particles can be obtained by laser particle size analyzer testing.

[0043] In some embodiments, the lithium manganese iron phosphate is doped with a first doping element, and the first doping element includes at least one of K, Na, Cu, Zn and Ni, that is, the first doping element can be any one of the element types listed above, such as K, Na, Cu, Zn or Ni, etc.; the first doping element can also be a combination of K or Ni, or a combination of K and Cu, or a combination of K and Zn, or a combination of Na and Cu, or a combination of Zn and Ni, or a combination of Na and Ni, or a combination of K, Cu and Ni, or a combination of K, Na, Zn and Ni, etc., which are not listed here one by one. In addition, when the first doping element is a combination of two or more, there is no restriction on the proportion of each element in the combination.

[0044] In some embodiments, the content of the first doping element in lithium manganese iron phosphate is any value between 1 and 200 ppm, for example, it can be 1 ppm, 2 ppm, 5 ppm, 6 ppm, 10 ppm, 15 ppm, 20 ppm, 30 ppm, 40 ppm, 45 ppm, 50 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 150 ppm, 170 ppm or 200 ppm.

[0045] In some embodiments, the lithium nickel cobalt manganese oxide is doped with a second doping element, and the second doping element includes at least one of Fe, Na, and Ca, that is, the second doping element can be any one of the element types listed above, such as Fe, Na, or Ca, etc. The second doping element can also be a combination of Fe and Na, or a combination of Fe and Ca, or a combination of Na and Ca, or a combination of Fe, Na, and Ca, etc., which are not listed here one by one. In addition, when the second doping element is a combination of two or more, there is no restriction on the proportion of each element in the combination.

[0046] In some embodiments, the content of the second doping element in the lithium nickel cobalt manganese oxide is any value between 20 and 200 ppm, for example, 20 ppm, 22 ppm, 25 ppm, 27 ppm, 30 ppm, 35 ppm, 40 ppm, 50 ppm, 70 ppm, 80 ppm, 100 ppm, 110 ppm, 120 ppm, 140 ppm, 150 ppm, 170 ppm or 200 ppm.

[0047] In some embodiments, the thickness of the positive electrode active material layer located on any side of the positive electrode current collector is any value between 40 and 100 μm, for example, it can be 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0048] In some embodiments, the compaction density of the positive electrode active material layer is 3 to 3.2 g / cm 3 Any value in, for example, 3g / cm 3 、3.05g / cm 3 、3.1g / cm 3 、3.15g / cm 3 or 3.2g / cm 3 .

[0049] In some embodiments, the thickness of the negative electrode active material layer on any side of the negative electrode current collector is any value between 50 and 100 μm, for example, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0050] In some embodiments, the compaction density of the negative electrode active material layer is 1.45 to 1.8 g / cm 3 Any value in, for example, 1.45 g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 or 1.8 g / cm 3 .

[0051] The composition and preparation method of the electrochemical device provided by the present invention can be carried out by conventional methods in the art. For example, the specific preparation process of the electrochemical device is as follows:

[0052] Preparation of positive electrode sheet: positive electrode material, positive electrode conductor, positive electrode binder, positive electrode dispersant are mixed according to the weight ratio of (87 to 96.5): (1 to 3): (1.5 to 4): (0.01 to 1), solvent N-methylpyrrolidone (NMP) is added, and the solid content of the slurry is adjusted to 40% to 70%, and then fully stirred and mixed under the action of a vacuum mixer to obtain positive electrode slurry; the positive electrode slurry is mixed according to 0.2g to 0.4g / 1540.25mm 2 The positive electrode current collector is uniformly coated with a surface density of 10000 square meters, and the positive electrode current collector is dried, and then cold pressed and cut to obtain a positive electrode sheet. Among them, the positive electrode material includes lithium iron manganese phosphate and lithium nickel cobalt manganese oxide, and the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is (0.6 to 0.8): (0.2 to 0.4); the positive electrode conductive agent can be selected from at least one of carbon black (SuperP), acetylene black, carbon nanotubes (CNT), graphene, nano carbon fiber (VGCF) and other conductive materials, for example, the positive electrode conductive agent is SP and CNT, and the mass ratio of SP and CNT is 2:1; the positive electrode binder can be selected from at least one of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), for example, the binder can be PVDF. The positive electrode dispersant can be selected from one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, polyacrylic acid, and polyacrylate.

[0053] Preparation of negative electrode sheet: negative electrode material, negative electrode conductive agent, negative electrode binder, negative electrode dispersant are mixed in a mass ratio of (93 to 98): (0.2 to 1.5): (1 to 3): (0.01 to 1.5), deionized water is added, and the solid content of the slurry is adjusted to 40% to 70%, and then the slurry is fully stirred and mixed under the action of a vacuum mixer to obtain a negative electrode slurry; the negative electrode slurry is mixed at 0.13g to 0.22g / 1540.25mm 2 The negative electrode current collector is uniformly coated with a surface density of 100%, the negative electrode current collector is dried, and then cold pressed and cut to obtain the negative electrode sheet. Among them, the negative electrode material can be selected from at least one of carbon-based materials (such as graphite, hard carbon or soft carbon) and silicon-based materials (such as silicon oxide or carbon-silicon composite materials). The negative electrode conductive agent can be selected from at least one of conductive materials such as carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, nano-carbon fibers (VGCF); the negative electrode binder is selected from at least one of binding materials such as polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR); the negative electrode dispersant can be selected from at least one of polyvinyl pyrrolidone (PVP), sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA).

[0054] Preparation of diaphragm: The diaphragm is made of PE or PP porous membrane, and PP / PE / PP porous membrane can be selected, with a thickness of 9μm to 18μm, such as 9μm, 12μm, 16μm or 18μm; the air permeability is 180s / 100mL to 380s / 100mL, such as 180s / 100mL, 280s / 100mL or 380s / 100mL; the porosity is 30% to 50%, such as 30%, 40% or 50%.

[0055] Electrolyte: The electrolyte in the present application can be selected from conventional types of electrolytes in the art. For example, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 20:20:60 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0056] Assemble the battery: stack or wind the positive electrode sheet, separator, and negative electrode sheet prepared above in sequence, so that the separator is placed between the positive and negative electrode sheets to play a role of isolation. Then package them (such as wrapping them with aluminum plastic film), transfer them to a vacuum oven for drying to make the water content below 450ppm, then inject electrolyte and seal them, and finally prepare a lithium-ion battery after standing, hot and cold pressing, formation, clamping, capacity division and other processes.

[0057] On the other hand, the present invention provides an electric device, which includes the electrochemical device described in any of the above embodiments, and the electrochemical device can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc. The vehicle can be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc.; the spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc.; the electric toy includes a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy and an electric airplane toy, etc.; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, for example, an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The embodiments of the present application do not impose any special restrictions on the above-mentioned electric devices.

[0058] The technical scheme of the present invention is described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available products or can be prepared by conventional methods in the art.

[0059] Example 1

[0060] This embodiment provides an electrochemical device, and the preparation process of the electrochemical device is as follows:

[0061] S1. Preparation of positive electrode sheet: positive electrode material, positive electrode conductive agent (SP and CNT, SP and CNT mass ratio is 8:5), positive electrode binder PVDF, positive electrode dispersant PVP are mixed in a mass ratio of 96.5:1.3:2.1:0.1, solvent N-methylpyrrolidone (NMP) is added, and the solid content of the slurry is adjusted to 55%, and then the positive electrode slurry is fully stirred and mixed under the action of a vacuum mixer; the positive electrode slurry is evenly coated on a 13μm thick positive electrode current collector aluminum foil, transferred to an oven for drying, and then cold pressed and cut to obtain positive electrode sheets. Among them, the positive electrode material includes lithium iron manganese phosphate LiMn 0.6 Fe 0.4 PO4 and LiNi 0.6 Co 0.2 Mn 0.2 The mass ratio of O2, lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is 7:3.

[0062] S2. Preparation of negative electrode sheets: Mix the negative electrode material artificial graphite, the negative electrode conductive agent SP, the negative electrode binder styrene-butadiene rubber (SBR), and the negative electrode dispersant PVP in a mass ratio of 97.5:0.9:1.5:0.1, add deionized water, adjust the solid content of the slurry to 55%, and then stir and mix thoroughly under the action of a vacuum mixer to obtain a negative electrode slurry; evenly coat the negative electrode slurry on both sides of a 6 μm thick copper foil of a negative electrode current collector, transfer to an oven for drying, and then obtain a negative electrode sheet by cold pressing and slitting.

[0063] S4. Diaphragm preparation: A 10 μm thick polyethylene (PE) diaphragm was selected.

[0064] S5. Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 20:20:60 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0065] S6, assembling the battery: stack the above-prepared negative electrode sheet, separator, and positive electrode sheet in order, and put them into aluminum plastic film to obtain a dry battery cell, and bake the dry battery cell to remove water. Inject the prepared electrolyte into the dry battery cell and encapsulate it to obtain a finished soft-pack lithium-ion battery with a capacity of 1.2Ah.

[0066] Example 2

[0067] This embodiment provides an electrochemical device with the same system as that of embodiment 1. The difference between this embodiment and embodiment 1 is that the lithium manganese iron phosphate material in the positive electrode material is LiMn 0.65 Fe 0.35 PO4.

[0068] Example 3

[0069] This embodiment provides an electrochemical device of the same system as that of Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode material is adjusted to 8:2.

[0070] Example 4

[0071] This embodiment provides an electrochemical device of the same system as that of Embodiment 1. The difference between this embodiment and Embodiment 1 is that the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode material is adjusted to 6:4.

[0072] Example 5

[0073] This embodiment provides an electrochemical device with the same system as that of embodiment 1. The difference between this embodiment and embodiment 1 is that in the positive electrode material, the lithium nickel cobalt manganese oxide material is LiNi 0.86 Co0.06 Mn 0.08 O2, the median particle size D2 of nickel cobalt manganese oxide material is 3.3μm.

[0074] Comparative Example 1

[0075] This comparative example provides an electrochemical device of the same system as that of Example 1. The difference between this comparative example and Example 1 is that in the positive electrode material, lithium manganese iron phosphate is LiMn 0.55 Fe 0.45 PO4, the median particle size D1 of lithium manganese iron phosphate particles is 0.65μm; lithium nickel cobalt manganese oxide is LiNi 0.6 Co 0.2 Mn 0.2 O2, the median particle size D2 of lithium nickel cobalt manganese oxide particles is 3.6 μm; the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is adjusted to 7:3.

[0076] Comparative Example 2

[0077] This comparative example provides an electrochemical device of the same system as that of comparative example 1. The difference between this comparative example and comparative example 1 is that in the positive electrode material, the median particle size D1 of the lithium manganese iron phosphate particles is 0.6 μm; the lithium nickel cobalt manganese oxide is LiNi 0.6 Co 0.2 Mn 0.2 O2, the median particle size D2 of lithium nickel cobalt manganese oxide particles is 3.4 μm; the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is adjusted to 8:2.

[0078] Comparative Example 3

[0079] This comparative example provides an electrochemical device of the same system as that of comparative example 2. The difference between this comparative example and comparative example 2 is that the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is adjusted to 7.5:2.5.

[0080] Comparative Example 4

[0081] This comparative example provides an electrochemical device of the same system as that of comparative example 2. The difference between this comparative example and comparative example 2 is that the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is adjusted to 6:4.

[0082] Comparative Example 5

[0083] This comparative example provides an electrochemical device of the same system as comparative example 2. The difference between this comparative example and comparative example 1 is that in the positive electrode material, the median particle size D1 of the lithium iron manganese phosphate particles is 0.5 μm, and the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is adjusted to 7:3.

[0084] Comparative Example 6

[0085] This comparative example provides an electrochemical device of the same system as comparative example 1. The difference between this comparative example and comparative example 1 is that in the positive electrode material, the median particle size D1 of the lithium iron manganese phosphate particles is 0.6 μm; the median particle size D2 of the lithium nickel cobalt manganese oxide particles is 4 μm, and the mass ratio of lithium iron manganese phosphate and lithium nickel cobalt manganese oxide is adjusted to 7:3.

[0086] The batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were subjected to cycle performance tests to verify the improvement effect of the embodiments of the present invention on the cycle performance of electrochemical devices. The test results are shown in Table 1, and the test method is as follows:

[0087] Battery cycle performance test: At 45°C, the battery was subjected to 500 charge and discharge cycle tests at a current rate of 1C / 1C, the 1st cycle discharge capacity and the 500th cycle discharge capacity of the battery were recorded, and the capacity retention rate of the battery after 500cls of cycling was calculated (500cls capacity retention rate = 500cls discharge capacity / 1cls discharge capacity).

[0088] Table 1: Performance test results of batteries prepared in Examples 1 to 5 and Comparative Examples 1 to 6

[0089]

[0090] By comparing the test results of Examples 1 to 5 and Comparative Examples 1 to 6, it can be seen that when the positive electrode material in the electrochemical device satisfies the relationship shown in Formula I, the lithium nickel cobalt manganese oxide material in the positive electrode material can effectively share the current in the charge range corresponding to the Mn potential platform in the lithium manganese iron phosphate, so as to improve the charge and discharge efficiency of the electrochemical device at high potential, make full use of the capacity of the lithium manganese iron phosphate at high potential, maintain the electrochemical stability of the lithium manganese iron phosphate at high potential, and thus optimize the cycle performance of the electrochemical device.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An electrochemical device, characterized in that: The electrochemical device comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprises a positive electrode material; the positive electrode material comprises lithium manganese iron phosphate and lithium nickel cobalt manganese oxide; The positive electrode material satisfies the relationship of formula I: Among them, A is the mass proportion of the lithium manganese iron phosphate in the lithium manganese iron phosphate and the nickel cobalt manganese oxide, and 0.6≤A≤0.8; D1 is the median particle size Dv50 of the lithium manganese iron phosphate, and D2 is the median particle size Dv50 of the nickel cobalt manganese oxide; Q1 is the gram capacity of the lithium manganese iron phosphate when the potential of the electrochemical device is higher than 3.95V, 80mAh / g≤Q1≤92mAh / g; Q2 is the gram capacity of the nickel cobalt manganese oxide when the potential of the electrochemical device is higher than 3.95V, Q2≥80mAh / g.

2. The electrochemical device according to claim 1, characterized in that D1 is greater than or equal to 0.59 μm, and D2 is less than or equal to 3.5 μm.

3. The electrochemical device according to claim 2, characterized in that The lithium manganese iron phosphate is a secondary particle, and the median particle size Dv50 of the primary particles contained in the secondary particles is 0.1 to 0.3 μm.

4. The electrochemical device according to claim 1, characterized in that The lithium iron manganese phosphate is LiMn x Fe (1-x) PO4, where 0.6≤x≤0.

8.

5. The electrochemical device according to claim 1 or 4, characterized in that: The lithium manganese iron phosphate is doped with a first doping element, and the first doping element includes at least one of K, Na, Cu, Zn and Ni.

6. The electrochemical device according to claim 1, characterized in that The lithium nickel cobalt manganese oxide is LiNi a Co b Mn c O2, where a+b+c=1, a≥0.

6.

7. The electrochemical device according to claim 6, characterized in that In the lithium nickel cobalt manganese oxide LiNi a Co b Mn c In O2, 0.8≤a≤0.

88.

8. The electrochemical device according to claim 1 or 6, characterized in that: The lithium nickel cobalt manganese oxide is doped with a second doping element, and the second doping element includes at least one of Fe, Na, and Ca.

9. The electrochemical device according to claim 1, characterized in that The thickness of the positive electrode active material layer located on at least one side of the positive electrode current collector is 40 to 100 μm; the compaction density of the positive electrode active material layer is 3 to 3.2 g / cm 3 ; And / or, the electrochemical device further comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the thickness of the negative electrode active material layer located on at least one side of the negative electrode current collector is 50 to 100 μm; the compaction density of the negative electrode active material layer is 1.45 to 1.8 g / cm 3 .

10. An electrical device, characterized in that: The electrical device comprises the electrochemical device according to any one of claims 1 to 9.

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