Hybrid energy storage device with high energy density and long cycle life

Abstract

The invention discloses a hybrid energy storage device with high energy density and long cycle life, and relates to the technical field of electrochemistry. Comprising a positive electrode, a negative electrode, a diaphragm and an electrolyte, the positive electrode material is powder formed by connecting layered lithium-containing metal oxide and activated carbon in parallel, lithium cobalt oxide LCO or a lithium-rich manganese base with a set proportion is added into the layered lithium-containing metal oxide, and the negative electrode material is formed by mixing hard carbon and mesocarbon microbeads. According to the lithium ion hybrid capacitor provided by the invention, the energy density can be close to 100Wh / Kg, the power pulse is 10s, the Imax is close to 140C, the cycle life is longer than 100000 times, the current mainstream lithium ion capacitor and high-power battery application scenarios can be fully covered, and the blank of products with high energy density and high power performance is filled.

Description

Technical Field

[0001] The invention relates to the field of electrochemical technology, and in particular to a hybrid energy storage device with high energy density and long cycle life. Background Art

[0002] Hybrid energy storage devices are a new type of energy storage system, including hybrid supercapacitors, hybrid battery capacitors and / or other hybrid battery components. They combine the material intercalation chemical energy storage mechanism of ion batteries and the physical energy storage idea of ​​adsorption and desorption of porous large specific surface area activated carbon of supercapacitors. In terms of performance, their energy density and power are between ion batteries and supercapacitors, and they have deep research significance and broad application prospects.

[0003] At present, the mainstream hybrid lithium-ion capacitors have low energy density (<80Wh / Kg), insufficient power density (pulse 10s Imax <100C), and a cycle life of basically 100,000 cycles. On the positive and negative electrode material side, the current mainstream hybrid capacitors are divided into two categories, one is the internal battery capacitance mechanism parallel system, and the other is the battery capacitance mechanism series system. In the parallel system, the positive electrode is mostly layered lithium-containing metal oxide to provide a lithium source for lithium ion intercalation and deintercalation, and is mixed with a certain proportion of porous activated carbon to provide a high-power response for physical adsorption and desorption. At the same time, the negative electrode is pre-embedded lithium or a conventional high-power small-particle carbon negative electrode. The battery and capacitor energy storage mechanism participate in the reaction in parallel. The hybrid capacitor of this structure has insufficient power density and a lifespan of only less than 50,000 cycles. In the internal series system, the positive electrode is mainly porous activated carbon to ensure the capacitance characteristics, and the negative electrode is mainly lithium-deintercalation carbon material with pre-lithium intercalation treatment. The lithium source is provided by electrolyte lithium salt. This structure has excellent power density and cycle life, but there is a shortcoming in energy density (<50Wh / Kg), and the usage scenarios are limited. Summary of the invention

[0004] The purpose of the present invention is to provide a hybrid energy storage device with high energy density and long cycle life to solve the problems existing in the above-mentioned prior art.

[0005] In order to solve the above problems, according to one aspect of the present invention, a hybrid energy storage device with high energy density and long cycle life is provided, including a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode material is a powder formed by layered lithium-containing metal oxide and activated carbon in parallel, and a set proportion of lithium cobalt oxide LCO or lithium-rich manganese base is added to the layered lithium-containing metal oxide, and the negative electrode material is composed of a mixture of hard carbon and mesophase carbon microspheres.

[0006] In a preferred embodiment of the present invention, the layered lithium-containing metal oxide is a nickel cobalt manganese oxide NCM system compound, the nickel cobalt manganese oxide NCM system compound has a D50 particle size of ≤5um, a high-voltage range capacity of greater than 165mAh / g, and the activated carbon is AC activated carbon.

[0007] In a preferred embodiment of the present invention, in the positive electrode material, the weight ratio of the layered lithium-containing metal oxide to the activated carbon is 8:2.

[0008] Furthermore, the addition ratio of the lithium cobalt oxide LCO or the lithium-rich manganese-based is 10-20% of the weight of the layered lithium-containing metal oxide.

[0009] In a preferred embodiment of the present invention, in the negative electrode material, the addition ratio of the mesocarbon microbeads is 20-30% of the weight of the hard carbon.

[0010] In a preferred embodiment of the present invention, the electrolyte includes a lithium salt, a solvent and a functional additive, wherein the lithium salt is a mixture of LiBF4 and LiPF6; the solvent is selected from one or more of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, vinyl methyl carbonate EMC, ethylene carbonate DEC, ethyl propionate EP, propyl propionate PP, ethyl acetate EA or propyl acetate PA; and the functional additive includes a stabilizer or a film-forming agent.

[0011] Furthermore, in the lithium salt, the weight of LiBF4 is 5% of the weight of LiPF6.

[0012] Furthermore, the solvent is a mixed solvent composed of ethylene carbonate EC and vinyl methyl carbonate EMC, and in the mixed solvent, the volume of the vinyl methyl carbonate EMC is 30% of the volume of the ethylene carbonate EC.

[0013] In a preferred embodiment of the present invention, the separator is high molecular weight polyethylene and polypropylene.

[0014] In a preferred embodiment of the present invention, the hybrid energy storage device has an energy density of 100Wh / Kg, a pulse of 10s, an Imax of 140C, and a cycle life of >100,000 times.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention re-matches the positive and negative electrode materials, re-regulates and designs the conductive agent binder in the positive and negative electrodes, performs multi-dimensional analysis and optimization on the electrolyte system, matches a new multifunctional insulating polymer diaphragm, and creatively designs a hybrid capacitor system with excellent lifespan, energy density, and power density;

[0017] 2. In the present invention, the positive electrode material is set to a layered lithium-containing metal oxide (mainly a high-pressure NCM ternary lithium-rich oxide, including a certain high-pressure LCO lithium cobalt oxide or a high-pressure lithium-rich manganese base) to further improve the voltage and energy density, and a certain proportion of activated carbon is connected in parallel to provide physical energy storage, because the capacity of the lithium-containing high-pressure metal oxide is high, and the activated carbon component of the positive electrode can be further expanded without sacrificing high energy density; the negative electrode is mainly hard carbon, assisted by a certain proportion of high-power graphite mesophase carbon microspheres, to ensure high rate response while improving energy density;

[0018] 3. The electrolyte obtained by screening from the perspective of hybrid energy storage devices in the present invention can ensure the stability of positive electrode high-voltage film formation, extend the positive electrode failure cycle, ensure efficient and stable ion transmission, and ensure the adaptability of the electrolyte in a wide temperature range;

[0019] 4. The diaphragm provided by the present invention has high rate, high porosity and low internal resistance to ensure the design of fast ion channels and low internal resistance devices, and has excellent performance in safety. After long-term life testing under multiple working conditions, the diaphragm still maintains excellent stability and safety.

[0020] 5. The hybrid energy storage device provided by the present invention has an energy density close to 100Wh / Kg, a power pulse of 10s, an Imax close to 140C, and a cycle life of >100,000 times. It can fully cover the current mainstream lithium-ion capacitor and high-power battery application scenarios, filling the gap in products with both high energy density and high power performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the structure of a hybrid energy storage device with high energy density and long cycle life provided by the present invention;

[0022] Figure 2 The SEM images of the hard carbon and mesophase carbon microspheres in the present invention. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings so that the purpose, features and advantages of the present invention can be more clearly understood. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.

[0024] In the following description, certain specific details are set forth for the purpose of illustrating the various disclosed embodiments to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments may be practiced without one or more of these specific details. In other cases, well-known devices, structures, and techniques associated with the present application may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0025] References throughout the specification to "one embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of "in one embodiment" or "in an embodiment" in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.

[0026] In the following description, in order to clearly show the structure and working mode of the present invention, many directional words will be used for description, but the words "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", "down", etc. should be understood as convenient terms and should not be understood as restrictive terms.

[0027] It should be noted that the features shown in the drawings of the present application may belong to one embodiment or to different embodiments, as long as there is no conflict between these features. In order to save space, the present application may use the same drawing to illustrate different embodiments, that is, the same drawing of the present application may be used to reflect the features in different embodiments.

[0028] like Figure 1 A hybrid energy storage device with high energy density and long cycle life is shown, including a positive electrode, a negative electrode, a separator and an electrolyte.

[0029] The positive electrode material is a powder formed by connecting high-pressure layered lithium-containing metal oxide and activated carbon in parallel, and the high-pressure layered lithium-containing metal oxide LiX m Y n Z 1-m-n O2 is a nickel cobalt manganese oxide NCM system compound, and the NCM system compound is mainly high-pressure NCM ternary lithium-rich oxide, containing a certain amount of high-pressure lithium cobalt oxide LCO or high-pressure lithium-rich manganese base, which can further improve the voltage and energy density, and at the same time, a certain proportion of activated carbon is connected in parallel to provide physical energy storage, because the capacity of lithium-containing high-pressure metal oxides is high. In the present invention, the activated carbon component of the positive electrode can be further expanded without sacrificing high energy density; among them, AC activated carbon is an activated carbon material with developed pores and large specific surface area, which can ensure the storage response capability of physical adsorption and desorption to anions and cations.

[0030] In the present invention, the selected NCM system compounds are described by taking NCM5 series, NCM6 series and NCM8 series as examples. The parameters of the NCM5 series, NCM6 series and NCM8 series compounds are shown in Table 1 below.

[0031] Table 1 Physical and chemical indicators of high pressure NCM

[0032]

[0033] From Table 1 above, it can be seen that the D50 particle size of NCM system compounds is ≤5μm, which meets the high current effect of high rate, and the capacity in the high voltage range is greater than 165mAh / g (conventional ternary gram capacity). Therefore, NCM system compounds are selected as positive electrode materials.

[0034] In addition, the NCM system compound of the positive electrode material of the present invention can also be mixed with a high-voltage lithium cobalt oxide LCO positive electrode material with a weight fraction of 10-20% of the NCM system compound, which has high compaction, can ensure energy density while further reducing thickness, and make a thinner positive electrode, which is beneficial to the response, deintercalation and diffusion of ions on the electrode surface. Among them, the physical and chemical indicators of the proportioned high-voltage lithium cobalt oxide LCO are shown in Table 2 below, with high potential and high compaction.

[0035] Table 2 Physical and chemical indicators of high-voltage lithium cobalt oxide LCO

[0036]

[0037] In addition, the NCM system compound of the positive electrode material of the present invention can also be mixed with a high-voltage lithium-rich manganese-based positive electrode material with a weight fraction of 10-20% of the NCM system compound, and its rate contribution accounts for a small proportion, mainly to ensure energy density. Among them, the physical and chemical indicators of the proportioned high-voltage lithium-rich manganese-based are shown in Table 3 below, which has the characteristics of high capacity, linear voltage curve, high voltage, and obvious prospect advantages.

[0038] Table 3 Physical and chemical indicators of high-voltage lithium-rich manganese-based

[0039]

[0040] In addition, at the negative electrode, Figure 1 As shown in FIG. 1 , the present invention adopts an amorphous small-particle carbonaceous negative electrode (hard carbon as the main body, assisted by a certain proportion of high-power graphite mesophase carbon microspheres) to ensure high-rate response while improving energy density. Among them, the SEM images of hard carbon and mesophase carbon microspheres are shown in FIG. Figure 2 shown.

[0041] Among them, hard carbon materials refer to amorphous carbon that is difficult to form a graphitized structure even at a high temperature of 2500°C; it can generally be obtained by thermal decomposition of high molecular polymers, and hard carbon can be obtained by thermal decomposition of resins with cross-linked structures at 1000°C; hard carbon has an amorphous structure, and the carbon atomic layers are arranged in disordered layers, and are anisotropically arranged on a macroscopic scale; the spacing between carbon atomic layers is greater than 0.38nm, which means that Li + When embedded in hard carbon, there is almost no volume expansion, and it has ideal cycle stability; and the large interlayer spacing also makes Li + It is easier to embed in it, so it has excellent high current discharge performance.

[0042] As a high-rate graphite negative electrode, mesophase carbon microspheres are the products obtained by high-temperature graphitization of easily graphitized carbon (asphalt coke type). The spherical structure is conducive to close stacking. Compared with natural graphite, MCMB has a large specific surface area, and the edge positions of the carbon layer and irregular defect positions can provide lithium storage space, with a relatively high specific capacity. MCMB has excellent conductivity, high cycle stability, and good rate performance.

[0043] In the present invention, the negative electrode is mainly composed of hard carbon, and the mesophase carbon microbeads account for 20-30%.

[0044] After the screening of positive and negative electrode materials is completed, in order to comply with the above positive and negative electrode material matching logic, the present invention designs and optimizes the electrolyte formula for the system, and analyzes the functional electrolyte in multiple dimensions, mainly including ① designing multifunctional additives suitable for high-voltage positive electrodes to ensure the stability of positive electrode high-voltage film formation and extend the positive electrode failure cycle; ② studying fast ion migration systems, and multipolar solvents to ensure efficient and stable ion transmission; ③ studying functional additives suitable for small-particle-size, wide-interlayer, high-rate negative electrodes, focusing on the negative electrode film formation characteristics; ④ conducting solvent regulation for a wide temperature range and multiple working conditions to ensure the adaptability of wide temperature range electrolytes,

[0045] Preferably, the electrolyte system of the present invention includes lithium salt, solvent and functional additive. Among the lithium salts of the present invention, LiPF6 is the main component, which has a decomposition temperature of 80-130°C, high conductivity, low internal resistance, and is easy to decompose when in contact with water. A certain amount (5%) of LiBF4 is compounded, and its low temperature performance and rate performance are good, but a stable SEI film cannot be formed.

[0046] As for the solvent, the solvents shown in Table 4 can be selected. In the present invention, EC-based solvents are preferably selected and mixed with a certain amount of EMC (30%) to ensure high rate and low internal resistance while having good cycle stability.

[0047] Among the functional additives, high-voltage stabilizers are added to high-voltage positive electrodes to ensure that the positive electrode film is dense and prolongs the positive electrode aging cycle. VC negative electrode film-forming agents are added to assist the negative electrode film formation and prolong the cycle period. DOD is added to ensure that the fast ion transmission rate meets the high-frequency response of hybrid energy storage devices.

[0048] Table 4 Electrolyte solvent system

[0049]

[0050] In addition, in response to the above-mentioned system requirements, the present invention also selects a high-rate, high-porosity, low-internal-resistance polymer membrane, preferably high-molecular-weight polyethylene and polypropylene, to ensure the design of fast ion channels and low-internal-resistance devices, and has excellent performance in safety. After long-term life testing under multiple working conditions, the diaphragm still maintains excellent stability and safety.

[0051] The lithium ion hybrid capacitor designed by the present invention has an energy density of nearly 100Wh / Kg and a power pulse of 10s. max Close to 140C, with a cycle life of >100,000 times, it can fully cover the current mainstream lithium-ion capacitor and high-power battery application scenarios, filling the gap in products with both high energy density and high power performance.

[0052] The preferred embodiments of the present invention have been described in detail above, but it should be understood that after reading the above teachings of the present invention, those skilled in the art may make various changes or modifications to the present invention. These equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A hybrid energy storage device with high energy density and long cycle life, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode material is a powder formed by connecting layered lithium-containing metal oxide and activated carbon in parallel, and the layered lithium-containing metal oxide LiX m Y n Z 1-m-n O2 is a nickel cobalt manganese oxide NCM system compound, and lithium cobalt oxide LCO or lithium-rich manganese base is added to the nickel cobalt manganese oxide NCM system compound, and the negative electrode material is composed of a mixture of hard carbon and intermediate phase carbon microspheres; the electrolyte includes lithium salt, solvent and functional additives, and the lithium salt is a mixture of LiBF4 and LiPF6; the solvent is selected from one or more of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, vinyl methyl carbonate EMC, ethylene carbonate DEC, ethyl propionate EP, propyl propionate PP, ethyl acetate EA or propyl acetate PA; the functional additive includes a stabilizer or a film-forming agent.

2. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: The D50 particle size of the nickel cobalt manganese oxide NCM system compound is ≤5 μm, and the capacity in the high-voltage range is greater than 165 mAh / g; the activated carbon is AC activated carbon.

3. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: In the positive electrode material, the weight ratio of the layered lithium-containing metal oxide to the activated carbon is 8:

2.

4. The hybrid energy storage device with high energy density and long cycle life according to any one of claims 1 to 3, characterized in that: The addition ratio of the lithium cobalt oxide LCO or the lithium-rich manganese base is 10-20% of the weight of the layered lithium-containing metal oxide.

5. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: In the negative electrode material, the addition ratio of the mesophase carbon microbeads is 20-30% of the weight of the hard carbon.

6. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: The lithium nickel cobalt manganese oxide NCM system compounds are NCM5 system, NCM6 system and NCM8 system compounds.

7. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: In the lithium salt, the weight of LiBF4 is 5% of the weight of LiPF6.

8. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: The solvent is a mixed solvent consisting of ethylene carbonate (EC) and vinyl methyl carbonate (EMC), and in the mixed solvent, the volume of the vinyl methyl carbonate (EMC) is 30% of the volume of the ethylene carbonate (EC).

9. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: The separator is high molecular weight polyethylene and polypropylene.

10. The hybrid energy storage device with high energy density and long cycle life according to claim 1, characterized in that: The hybrid energy storage device has an energy density of 100 Wh / Kg, a pulse of 10s, an Imax of 140C, and a cycle life of >100,000 times.

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