Battery, energy storage device and energy storage system

Abstract

The invention provides a battery, an energy storage device and an energy storage system. The battery provided by the embodiment of the invention comprises a positive pole piece, a diaphragm, a negative pole piece and an electrolyte, the electrolyte comprises a non-free-state electrolyte and a free-state electrolyte, the free-state electrolyte and the non-free-state electrolyte both comprise vinylene carbonate, the mass fraction of the vinylene carbonate in the non-free-state electrolyte is b1, and the unit is%; the mass fraction of vinylene carbonate in the free electrolyte is b2, the battery is charged and discharged at 25 DEG C under 0.5 P, and when the cycle capacity retention ratio is greater than or equal to 99.5%, the electrolyte meets the condition that b1 / b2 is greater than or equal to 0.1 and less than or equal to 0.5; wherein the non-free electrolyte comprises an electrolyte adsorbed on the positive pole piece, an electrolyte adsorbed on the diaphragm and an electrolyte adsorbed on the negative pole piece. The battery provided by the embodiment of the invention has relatively high cycle performance.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to a battery, an energy storage device, and an energy storage system. Background Art

[0002] With the continuous development of lithium-ion battery technology, lithium-ion batteries have advantages over other types of batteries such as lead-acid and nickel-cadmium batteries, such as high specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, small size, and light weight. Currently, lithium-ion batteries are widely used in mobile phones, laptops, electric vehicles, energy storage cabinets and other fields, and their application range is becoming increasingly wider.

[0003] With the development of the energy storage industry, higher requirements are placed on the life attenuation and service life of lithium-ion batteries. However, the cycle performance of existing lithium-ion batteries is poor and needs to be improved. Summary of the Invention

[0004] The embodiments of the present application provide a battery having high cycle performance.

[0005] In a first aspect, an embodiment of the present application provides a battery, comprising a positive electrode plate, a separator, a negative electrode plate and an electrolyte; the electrolyte comprises a non-free electrolyte and a free electrolyte, both the free electrolyte and the non-free electrolyte comprise vinylene carbonate, the mass fraction of vinylene carbonate in the non-free electrolyte is b1, in units of %; the mass fraction of vinylene carbonate in the free electrolyte is b2, then when the battery is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the electrolyte satisfies 0.1≤b1 / b2≤0.5; wherein, the non-free electrolyte comprises an electrolyte adsorbed on the positive electrode plate, an electrolyte adsorbed on the separator and an electrolyte adsorbed on the negative electrode plate.

[0006] Furthermore, when the battery is charged and discharged at 25° C. and 0.5P, and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b1 of vinylene carbonate in the non-free electrolyte is in the range of: 0.5%≤b1%≤4%.

[0007] Furthermore, when the battery is charged and discharged at 25° C. and 0.5P, and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b2 of vinylene carbonate in the free electrolyte is in the range of: 3%≤b2%≤9%.

[0008] Furthermore, the electrolyte includes an organic solvent, the organic solvent includes a cyclic carbonate and a chain carbonate, and the organic solvent includes 50% to 80% of the chain carbonate and 20% to 50% of the cyclic carbonate by mass.

[0009] Furthermore, the negative electrode active material includes graphite particles, and the graphite particles satisfy the following relationship: 0.8≤La / Lc≤1.6, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

[0010] Furthermore, the average crystallite length La of the graphite particles is in the range of 35 nm ≤ La ≤ 55 nm.

[0011] Furthermore, the average crystallite height Lc of the graphite particles is in the range of 30 nm ≤ Lc ≤ 45 nm.

[0012] Furthermore, the battery satisfies the relationship: 4≤b2×(La / Lc)≤10.

[0013] In a second aspect, an embodiment of the present application further provides an energy storage device, comprising:

[0014] cabinet; and

[0015] The battery described in the embodiment of the first aspect of the present application is accommodated in the box.

[0016] In a third aspect, an embodiment of the present application further provides an energy storage system, comprising:

[0017] The energy storage device according to the second embodiment of the present application; and

[0018] An electric energy conversion device, the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

[0019] The embodiment of the present application designs the ratio of the mass fraction of vinylene carbonate in the non-free electrolyte and the mass fraction of vinylene carbonate in the free electrolyte in the electrolyte, so that the mass fraction of vinylene carbonate in the free electrolyte is always greater than the mass fraction of vinylene carbonate in the non-free electrolyte, thereby being able to well control the mass fraction of vinylene carbonate in the non-free electrolyte within a certain range, and being able to well meet the amount of vinylene carbonate required for the battery to construct the initial SEI film without causing the impedance of the initial SEI film to be too large, thereby making the SEI film of the battery have better stability, thereby being able to reduce the side reactions of the battery, and making the battery have a higher cycle capacity retention rate and a longer cycle life; in addition, the SEI film can also have a lower impedance, and lithium plating is not likely to occur during the lithium insertion process of the negative electrode sheet, thereby making the battery have a higher cycle capacity retention rate and a longer cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 Schematic diagram of the structure of a battery according to an embodiment of the present application.

[0022] Figure 2 The battery of one embodiment of the present application is Figure 1 Schematic diagram of the cross-sectional structure in the AA direction.

[0023] Figure 3 It is a schematic cross-sectional structural diagram of a positive electrode plate according to an embodiment of the present application.

[0024] Figure 4 Schematic diagram of the structure of the negative electrode sheet of one embodiment of the present application.

[0025] Figure 5 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0026] Figure 6 This is a structural block diagram of an energy storage system according to an embodiment of the present application.

[0027] Figure 7 This is an application scenario diagram of the energy storage system of one embodiment of the present application.

[0028] Description of reference numerals:

[0029] 100-battery, 110-positive electrode plate, 111-positive electrode current collector, 112-positive electrode active layer, 120-diaphragm, 130-negative electrode plate, 131-negative electrode current collector, 132-negative electrode active layer, 140-housing, 150-end cover assembly, 200-energy storage device, 210-case, 300-energy storage system, 310-electric energy conversion device. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0032] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0033] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0034] Currently, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower. However, wind and solar energy are generally intermittent and highly volatile, which can cause grid instability, insufficient electricity during peak hours, and excessive electricity during off-peak hours. Unstable voltage can also damage electricity. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar power curtailment". To solve these problems, we must rely on energy storage. This means converting electrical energy into other forms of energy through physical or chemical means and storing them. When needed, this energy is converted into electrical energy and released. Simply put, energy storage is like a large "power bank", storing electricity when photovoltaic and wind energy are sufficient and releasing the stored electricity when needed.

[0035] Batteries are the smallest energy storage unit in energy storage devices and systems. Their performance directly impacts the performance and applications of these devices and systems. Batteries include lithium batteries (such as lithium-ion batteries) and sodium batteries (such as sodium-ion batteries).

[0036] With the continuous development of lithium-ion battery technology, lithium-ion batteries have demonstrated advantages over other types of batteries, such as lead-acid and nickel-cadmium batteries, including high specific capacity, no memory effect, high operating voltage, fast charging speed, wide operating temperature range, long cycle life, compact size, and light weight. Currently, lithium-ion batteries are widely used in mobile phones, laptops, electric vehicles, energy storage cabinets, and other fields, and their application is becoming increasingly broad. The development of the energy storage industry has placed higher demands on the lifespan degradation and service life of lithium-ion batteries. However, the cycle performance of existing lithium-ion batteries is poor and needs to be improved.

[0037] See Figure 1 and Figure 2, an embodiment of the present application provides a battery 100, wherein the battery 100 includes a positive electrode plate 110, a separator 120, a negative electrode plate 130 and an electrolyte.

[0038] Optionally, the battery 100 may be, but is not limited to, at least one of a lithium-ion battery, a lithium-sodium hybrid battery, and the like.

[0039] Optionally, the battery 100 may be, but is not limited to, at least one of a cylindrical battery, a square battery, a blade battery, etc. The drawings in this application illustrate only one or more possible forms of the battery 100 and should not be construed as limiting the battery 100 of the embodiments of this application.

[0040] It can be understood that the positive electrode sheet 110 and the negative electrode sheet 130 are respectively located on opposite sides of the separator 120 , that is, the separator 120 is located between the positive electrode sheet 110 and the negative electrode sheet 130 to separate the positive electrode sheet 110 from the negative electrode sheet 130 .

[0041] Optionally, the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly, which is then wound as a whole to form a bare cell. It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 can be collectively referred to as electrode sheets. In other words, the electrode sheet includes the positive electrode sheet 110 and the negative electrode sheet 130. Optionally, the electrode assembly can be, but is not limited to, a wound structure, a laminated structure, etc., which is not specifically limited in this application.

[0042] It should be noted that the positive electrode sheet 110 , the separator 120 and the negative electrode sheet 130 are at least partially immersed in the electrolyte.

[0043] See Figure 3 The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 . The positive electrode active layer 112 is disposed on the surface of the positive electrode current collector 111 .

[0044] It should be noted that the positive electrode active layer 112 can be provided on one surface of the positive electrode current collector 111, or on two opposite surfaces of the positive electrode current collector 111. In the following embodiments and accompanying drawings of the present application, the positive electrode sheet 110 is described and illustrated as including two layers of positive electrode active layers 112 (i.e., the positive electrode active layers 112 are provided on two opposite surfaces of the positive electrode current collector 111). This should not be construed as limiting the positive electrode sheet 110 of the embodiments of the present application.

[0045] Optionally, the material of the positive electrode current collector 111 may be, but is not limited to, aluminum foil, aluminum sheet, and the like.

[0046] Optionally, the positive electrode active layer 112 includes a positive electrode active material, a positive electrode conductor, a positive electrode binder, and a positive electrode thickener.

[0047] Optionally, the positive electrode active material may be, but is not limited to, at least one of a transition metal oxide, a Prussian blue analog, and a polyanionic compound. Optionally, the transition metal oxide may be, but is not limited to, at least one of NaCoO2, NaMnO2, and NaFeO2. Optionally, the Prussian blue analog may be, but is not limited to, at least one of Na2Mn(Fe(CN)6, NaFeFe(CN)6). The polyanionic compound may be, but is not limited to, sodium ferric phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP).

[0048] Optionally, the positive electrode active material may be, but is not limited to, lithium iron phosphate.

[0049] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0050] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0051] Optionally, the positive electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0052] Optionally, the diaphragm 120 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 120 , and the like.

[0053] See Figure 4 Optionally, the negative electrode sheet 130 includes a negative electrode current collector 131 and a negative electrode active layer 132, and the negative electrode active layer 132 is disposed on the surface of the negative electrode current collector 131. It can be understood that the negative electrode active layer 132 can cover one surface or two opposite surfaces of the negative electrode current collector 131.

[0054] Optionally, the negative electrode current collector 131 may be, but is not limited to, at least one of a copper sheet, a copper foil, and the like.

[0055] Optionally, the negative electrode active layer 132 includes a negative electrode active material, a negative electrode conductor, a negative electrode binder, and a negative electrode thickener.

[0056] Alternatively, the negative electrode active material may be, but is not limited to, a carbon material. Alternatively, the carbon material may be, but is not limited to, hard carbon.

[0057] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0058] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0059] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0060] In some embodiments, the electrolyte includes a non-free electrolyte and a free electrolyte, and both the free electrolyte and the non-free electrolyte include vinylene carbonate (abbreviated as VC), and the mass fraction of vinylene carbonate in the non-free electrolyte is b1, and the unit is %; the mass fraction of vinylene carbonate in the free electrolyte is b2, then the battery 100 is charged and discharged at 0.5P at 25°C, and when the cycle capacity retention rate is greater than or equal to 99.5%, the electrolyte satisfies 0.1≤b1 / b2≤0.5; wherein, the non-free electrolyte includes the electrolyte adsorbed on the positive electrode plate 110, the electrolyte adsorbed on the diaphragm 120, and the electrolyte adsorbed on the negative electrode plate 130.

[0061] It should be noted that the electrolyte adsorbed on the positive electrode sheet 110 includes the electrolyte adsorbed on the surface of the positive electrode sheet 110 and the electrolyte present in the pores of the positive electrode sheet 110; the electrolyte adsorbed on the separator 120 includes the electrolyte adsorbed on the surface of the separator 120 and the electrolyte present in the pores of the separator 120; and the electrolyte adsorbed on the negative electrode sheet 130 includes the electrolyte adsorbed on the surface of the negative electrode sheet 130 and the electrolyte present in the pores of the negative electrode sheet 130. Non-free electrolyte refers to the electrolyte remaining after the battery 100 is disassembled and the electrode assembly (positive electrode sheet 110, separator 120, and negative electrode sheet 130) is removed.

[0062] 0.5P refers to 0.5 times the rated power.

[0063] The battery 100 is charged and discharged at 25° C. and 0.5P, and the cycle capacity retention rate is greater than or equal to 99.5%, which means that when the battery 100 is charged and discharged at 25° C. and 0.5P, the ratio of the current test capacity to the rated capacity of the battery 100 is greater than or equal to 99.5%.

[0064] It should be noted that vinylene carbonate, as a film-forming additive of battery 100, participates in the formation and repair of the solid electrolyte interface film (SEI film for short) of battery 100 during the formation and circulation process of battery 100, so as to improve the stability of the SEI film of battery 100.

[0065] In this embodiment, the non-free electrolyte exists in the pores of the positive electrode sheet 110, the separator 120 and the negative electrode sheet 130. The non-free electrolyte is in direct contact with the positive electrode sheet 110, the negative electrode sheet 130 and the separator 120, and dominates the formation and repair process of the SEI film of the battery 100, participates in the desolvation effect of active metal ions (such as lithium ions), and directly determines the impedance R of the SEI film in the battery 100. SEI and charge transfer impedance Rct; the free electrolyte exists in the cavity of the battery 100 outside the pores of the positive electrode sheet 110, the diaphragm 120 and the negative electrode sheet 130, and there is no absolute physical barrier to the non-free electrolyte. When the non-free electrolyte is insufficiently consumed, the free electrolyte is automatically absorbed as a supplement through the capillary action of the electrode and the diaphragm 120. When the mass fraction of a component in the non-free electrolyte is higher than the mass fraction of the component in the free electrolyte, the non-free electrolyte can absorb the free electrolyte to reduce the mass fraction of the component in the non-free electrolyte; when the mass fraction of a component in the non-free electrolyte is lower than the mass fraction of the component in the free electrolyte, the non-free electrolyte absorbs the free electrolyte to increase the mass fraction of the component in the non-free electrolyte. There are dynamic differences in the electrolyte compositions of the two regions during the cycle consumption process, so the component contents of the battery 100 also change dynamically during use.

[0066] It is understood that during the first charge-discharge cycle of the battery 100, the ratio of the mass fraction b1 of vinylene carbonate in the non-free electrolyte to the mass fraction b2 of vinylene carbonate in the free electrolyte is any value between 0.1 and 0.5. Specifically, the value of b1 / b2 can be, but is not limited to, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, 0.33, 0.35, 0.38, 0.4, 0.43, 0.45, 0.48, 0.5, etc. If b1 / b2 is too small, it may be that b1 is too small or b2 is too large; if the mass fraction b1 of vinylene carbonate in the non-free electrolyte is too small, the initial SEI formed by the battery 100 is less stable, and the side reactions at the interface of the negative electrode plate 130 cannot be effectively suppressed in the initial stage of the cycle, which will consume active lithium, deteriorate the capacity, and thus deteriorate the cycle life; if the mass fraction b2 of vinylene carbonate in the free electrolyte is too large, the impedance after SEI repair during the cycle will be too large, it will be difficult for the negative electrode plate 130 to embed lithium, and lithium plating will easily occur, thereby deteriorating the cycle life of the battery 100. If b1 / b2 is too large, then b1 may be too large or b2 may be too small; if the mass fraction b1 of vinylene carbonate in the non-free electrolyte is too large, the battery 100 will form a film too thick during the formation stage, resulting in excessive initial SEI impedance, increasing the polarization of the negative electrode 130, affecting the capacity of the battery 100, and increasing the risk of lithium plating; if the mass fraction b2 of vinylene carbonate in the free electrolyte is too small, the vinylene carbonate in the non-free electrolyte cannot be replenished, the initial SEI stability is poor, and after the SEI film is ruptured, it cannot be repaired, and side reactions continue to occur to consume active lithium, thereby worsening the cycle life of the battery 100.

[0067] Optionally, within the first 200 charge and discharge cycles of the battery 100, a ratio b1 / b2 of the mass fraction b1 of vinylene carbonate in the non-free electrolyte to the mass fraction b2 of vinylene carbonate in the free electrolyte is in a range of 0.1 to 0.5.

[0068] Furthermore, when the battery 100 is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the ratio b1 / b2 of the mass fraction b1 of vinylene carbonate in the non-free electrolyte to the mass fraction b2 of vinylene carbonate in the free electrolyte is in the range of 0.15 to 0.3. This allows both the non-free electrolyte and the free electrolyte to have a more appropriate mass fraction of vinylene carbonate, which can improve the stability of the SEI film of the battery 100, thereby reducing the side reactions of the battery 100, resulting in a higher cycle capacity retention rate and a longer cycle life. In addition, the SEI film can also have lower impedance, making it less likely for lithium plating to occur during the lithium insertion process of the negative electrode 130, thereby achieving a higher cycle capacity retention rate and a longer cycle life.

[0069] The embodiment of the present application designs the ratio of the mass fraction of vinylene carbonate in the non-free electrolyte and the mass fraction of vinylene carbonate in the free electrolyte in the electrolyte, so that the mass fraction of vinylene carbonate in the free electrolyte is always greater than the mass fraction of vinylene carbonate in the non-free electrolyte, thereby being able to well control the mass fraction of vinylene carbonate in the non-free electrolyte within a certain range, and being able to well meet the amount of vinylene carbonate required for the battery 100 to construct the initial SEI film without causing the impedance of the initial SEI film to be too large, thereby making the SEI film of the battery 100 have better stability, thereby being able to reduce the side reactions of the battery 100, and making the battery 100 have a higher cycle capacity retention rate and a longer cycle life; in addition, the SEI film can also have a lower impedance, and lithium plating is not likely to occur during the lithium insertion process of the negative electrode plate 130, thereby making the battery 100 have a higher cycle capacity retention rate and a longer cycle life.

[0070] In some embodiments, when the battery 100 is charged and discharged at 25° C. and 0.5P, and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b1 of vinylene carbonate in the non-free electrolyte is in the range of: 0.5%≤b1%≤4%.

[0071] Specifically, when the battery 100 is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b1 of vinylene carbonate in the non-free electrolyte can be but is not limited to 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.8%, 3.0%, 3.3%, 3.5%, 3.8%, 4.0%, etc.

[0072] In this embodiment, if the mass fraction b1 of vinylene carbonate in the non-free electrolyte is too low, the initial SEI formed by the battery 100 will have poor stability, and the side reactions at the interface of the negative electrode plate 130 cannot be effectively suppressed in the initial stage of the cycle, which will consume active lithium, deteriorate the capacity, and thus deteriorate the cycle life; if the mass fraction b1 of vinylene carbonate in the non-free electrolyte is too high, the battery 100 will form a too thick film during the formation stage, resulting in excessive initial SEI impedance, increased polarization of the negative electrode plate 130, affecting the capacity of the battery 100, and increasing the risk of lithium plating.

[0073] In some embodiments, when the battery 100 is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b2 of vinylene carbonate in the free electrolyte is in the range of: 3%≤b2%≤9%.

[0074] Specifically, when the battery 100 is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b2 of vinylene carbonate in the free electrolyte can be but is not limited to 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, etc.

[0075] In this embodiment, if the mass fraction b2 of vinylene carbonate in the free electrolyte is too low, the vinylene carbonate in the non-free electrolyte cannot be replenished, the initial SEI stability is poor, and after the SEI film is broken, it cannot be repaired, and side reactions continue to occur to consume active lithium, thereby worsening the cycle life of the battery 100; if the mass fraction b2 of vinylene carbonate in the free electrolyte is too high, the impedance after the SEI is repaired during the cycle will be too large, it will be difficult for the negative electrode plate 130 to embed lithium, and lithium plating will easily occur, thereby worsening the cycle life of the battery 100.

[0076] In some embodiments, the electrolyte includes an organic solvent, the organic solvent includes a cyclic carbonate and a chain carbonate, and the organic solvent includes 50% to 80% of the chain carbonate and 20% to 50% of the cyclic carbonate by mass.

[0077] It should be noted that both the free-state electrolyte and the non-free-state electrolyte contain an organic solvent.

[0078] Specifically, the mass fraction of the chain carbonate in the organic solvent may be, but is not limited to, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc. The chain carbonate participates in the solvation of metal ions (e.g., lithium ions), thereby being brought to the surface of the negative electrode sheet 130 to react. Therefore, if the mass fraction of the chain carbonate in the organic solvent is too high, side reactions of the negative electrode sheet 130 during film formation will increase, thereby reducing the cycle capacity retention rate of the battery 100. If the mass fraction of the chain carbonate in the organic solvent is too low, the viscosity of the electrolyte increases, and the wettability of the electrolyte to the positive electrode sheet 110 and the negative electrode sheet 130 is reduced. The electrolyte cannot fully penetrate the pores of the positive electrode sheet 110 and the negative electrode sheet 130, resulting in a reduction in the contact area between the positive electrode active material and the negative electrode active material and the electrolyte, and a significant increase in the charge transfer impedance (Rct) and the ohmic impedance (Rs), thereby increasing the impedance of the battery 100. In addition, the positive electrode sheet 110 and the negative electrode sheet 130 are The areas on the electrode 130 that are not wetted by the electrolyte cannot participate in the electrochemical reaction, causing some positive electrode active materials and some negative electrode active materials to "fail", affecting the capacity of the battery 100; furthermore, the poor wettability of the electrolyte will lead to uneven surface current distribution of the positive electrode plate 110 and the negative electrode plate 130, local overcharge / over-discharge, and accelerated structural degradation of the positive electrode active materials and the negative electrode active materials (such as cracking of the positive electrode active material and lithium dendrite growth of the negative electrode plate 130).

[0079] Specifically, the mass fraction of the cyclic carbonate in the organic solvent may be, but is not limited to, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc. Cyclic carbonate is the main film-forming component of the SEI film. When its content is insufficient, the SEI film becomes loose and porous. Therefore, if the mass fraction of cyclic carbonate in the organic solvent is too low, the SEI film of the battery 100 will be incomplete, reducing the cycle life of the battery 100. Chain carbonates have weaker antioxidant capacity than cyclic carbonates. If the content of cyclic carbonate is too low, the antioxidant capacity of the electrolyte will be reduced, resulting in a narrower electrochemical window of the electrolyte and prone to oxidative decomposition and gas expansion of the electrolyte. Furthermore, if the mass fraction of cyclic carbonate in the organic solvent is too low, the ionic conductivity of the electrolyte will be reduced, the internal resistance of the battery 100 will be increased, and the rate performance and kinetic performance of the battery 100 will be reduced. If the mass fraction of the cyclic carbonate in the organic solvent is too high, the SEI film will be too thick, the interfacial impedance of the SEI film will increase, and the rate performance of the battery 100 will be reduced; if the mass fraction of the cyclic carbonate in the organic solvent is too high, the viscosity of the electrolyte will be too high, which will reduce the migration rate of the metal ions and reduce the low-temperature cycle performance of the battery 100.

[0080] Optionally, the cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), etc. The dielectric constant of ethylene carbonate is much greater than that of propylene carbonate, and ethylene carbonate can better promote the formation of SEI film.

[0081] Optionally, the chain carbonate may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like.

[0082] Optionally, the electrolyte solution further includes an electrolyte salt.

[0083] Alternatively, the electrolyte salt may be, but is not limited to, a lithium salt.

[0084] Optionally, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorodioxalatophosphate (LiODFP), lithium difluorooxalatoborate (LiODFB), lithium difluorophosphate (LiPO2F2), lithium trifluoromethanesulfonate (CF3SO3Li), etc.

[0085] Optionally, the molar concentration M of the electrolyte salt in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L. In the electrolyte, the molar concentration M of the electrolyte salt in the electrolyte may be, but is not limited to, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, etc. If the molar concentration M of the electrolyte salt in the electrolyte is too small, the concentration of free ions in the electrolyte is too small, which reduces the conductivity of the electrolyte and thus reduces the kinetic performance of the battery 100; if the molar concentration M of the electrolyte salt in the electrolyte is too large, a portion of the electrolyte salt is likely to remain undissociated, and the viscosity of the electrolyte will increase, which in turn reduces the conductivity of the electrolyte and also reduces the kinetic performance of the battery 100. When the molar concentration M of the electrolyte salt in the electrolyte is in the range of 0.7 mol / L≤M≤1.4 mol / L, the electrolyte can have a higher electrical conductivity, thereby enabling the battery 100 to have better kinetic performance.

[0086] Optionally, the electrolyte further comprises a film-forming additive other than vinylene carbonate. Optionally, the film-forming additive comprises at least one of fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl carbonate (VEC), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, adiponitrile, succinonitrile, and 1,3,6-hexanetrinitrile.

[0087] Optionally, the filling coefficient of the battery 100 ranges from 2.5 g / Ah to 5 g / Ah.

[0088] The "filling coefficient of the battery 100" refers to the mass of electrolyte required to be injected per unit rated capacity of the battery 100. For example, if the rated capacity of the battery 100 is 1000 Ah, the mass of electrolyte required to be injected into the battery 100 is 2500 g to 5000 g.

[0089] Specifically, the filling coefficient of the battery 100 can be, but is not limited to, 2.5g / Ah, 2.8g / Ah, 3.0g / Ah, 3.3g / Ah, 3.5g / Ah, 3.8g / Ah, 4.0g / Ah, 4.3g / Ah, 4.5g / Ah, 4.8g / Ah, 5g / Ah, etc. If the filling coefficient of the battery 100 is too low, the amount of electrolyte added to the battery 100 is too small, which may lead to insufficient wetting of the positive electrode sheet 110 and the negative electrode sheet 130, affecting the capacity of the battery 100. In addition, as the cycle proceeds, the electrolyte is continuously consumed, and dry areas are likely to appear on the positive electrode sheet 110 and the negative electrode sheet 130, causing the capacity retention rate of the battery 100 to drop too quickly. If the filling coefficient of the battery 100 is too high, the electrolyte exceeds the internal space of the battery 100 and cannot be injected.

[0090] Furthermore, the filling coefficient of the battery 100 ranges from 3 g / Ah to 4 g / Ah.

[0091] When injecting electrolyte into the battery 100, a portion of the electrolyte is injected first (i.e., the first injection), and then the battery is packaged, left to stand, and formed. Then, the remaining electrolyte is injected (the second injection, referred to as the second injection), and high-temperature standing and capacity testing are performed.

[0092] Optionally, the mass ratio of the electrolyte in the first injection of the battery 100 to the electrolyte in the second injection ranges from 65:35 to 90:10. Specifically, the mass ratio of the electrolyte in the first injection of the battery 100 to the electrolyte in the second injection can be, but is not limited to, 65:35, 70:30, 75:25, 80:00, 85:15, 90:10, etc. If the mass ratio of the electrolyte in the first injection of the battery 100 to the electrolyte in the second injection is too low, the content of vinylene carbonate in the electrolyte is too low, and the SEI film cannot be repaired in time during the cycle of the battery 100, which will deteriorate the later cycle of the battery 100. If the mass ratio of the electrolyte of the first injection of battery 100 to the electrolyte of the second injection is too high, the content of vinylene carbonate in the electrolyte will be too high. During the early cycle, the film formed on battery 100 will be too thick (i.e., the SEI film will be too thick), which will increase the resistance of the SEI film, reduce the dynamic performance of battery 100, and make lithium plating more likely to occur.

[0093] Furthermore, the mass ratio of the electrolyte of the first injection to the electrolyte of the second injection of the battery 100 ranges from 75:55 to 85:15.

[0094] In some embodiments, the negative electrode active material includes graphite particles, and the graphite particles satisfy the following relationship: 0.8≤La / Lc≤1.6, where La is an average crystallite length of the graphite particles, and Lc is an average crystallite height of the graphite particles.

[0095] It should be noted that the average crystallite length La of the graphite particles and the average crystallite height Lc of the graphite particles can be calculated from the X-ray diffraction pattern (XRD pattern) of the graphite particles.

[0096] The calculation formula for the average crystallite length La of graphite particles is: La = k1λ / β1cosθ1, where k1 = 1.84, λ = 0.154nm, β1 is the diffraction peak of the 110 crystal plane stacking of the graphite particles, θ1 is the half diffraction angle of the diffraction peak of the 110 crystal plane stacking in the XRD pattern of the graphite particles, k1 is a constant, and λ is the wavelength of the X-ray.

[0097] The calculation formula for the average crystallite height Lc of graphite particles is: Lc=k2λ / β2cosθ1, where k2=0.94, λ=0.154nm, β2 is the diffraction peak of the 002 crystal plane stacking of the graphite particles, θ2 is the half diffraction angle of the diffraction peak of the 002 crystal plane stacking in the XRD pattern of the graphite particles, k2 is a constant, and λ is the wavelength of the X-ray.

[0098] It is understood that the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles ranges from 0.8 to 1.6. In other words, the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles can be any value between 0.8 and 1.6.

[0099] Specifically, the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles can be, but is not limited to, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, etc.

[0100] In this embodiment, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is small, the expansion of the graphite particles in the z-axis (i.e., between graphite layers) direction when inserting lithium can be reduced, the damage to the SEI film on the surface of the graphite particles is reduced, the SEI rupture and recombination phenomenon caused by the expansion of the graphite particles is alleviated, and the VC required to repair the SEI is less. Therefore, the mass fraction of vinylene carbonate in the non-free electrolyte can be appropriately reduced to avoid increasing the lithium insertion resistance of the graphite particles due to the excessive mass fraction of vinylene carbonate in the non-free electrolyte, thereby affecting the cycle life; however, if the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is too small, the difficulty of preparing the graphite particles will increase, and the preparation cost of the graphite particles will increase. As the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles increases, the orientation degree of the graphite particles gradually increases (that is, the OI value gradually increases), the first efficiency (referred to as first efficiency) of the battery 100 using the graphite particles gradually decreases, and the cycle capacity retention rate of the battery 100 using the graphite particles also gradually decreases; therefore, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is too large, the orientation degree OI value of the graphite particles is high, which will increase the expansion of the graphite particles during the lithium insertion process, and reduce the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles. In this embodiment, the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, which results in a smaller orientation index OI value for the graphite particles and a greater degree of orientation (i.e., a greater number of orientation directions) within the graphite particles. During the lithium insertion process of the negative electrode plate 130, the lithium insertion stress can be better released, and the expansion of the negative electrode plate 130 in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery 100 during the charge and discharge cycle and improving the initial efficiency and cycle capacity retention rate of the battery 100. Furthermore, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, the battery 100 using the graphite particles can consume less during the initial film formation stage, reducing the rupture and recombination of the solid electrolyte interface film and the consumption of active lithium during the cycle, and improving the cycle capacity retention rate of the battery 100, thereby enabling the battery 100 to have a higher number of cycles and a longer cycle life.

[0101] In some embodiments, the average crystallite length La of the graphite particles is in the range of 35 nm ≤ La ≤ 55 nm.

[0102] Specifically, the average crystallite length La of the graphite particles can be, but is not limited to, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47nm, 48nm, 49nm, 50nm, 51nm, 52nm, 53nm, 54nm, 55nm, etc.

[0103] In this embodiment, as the average crystallite length La of the graphite particles increases, the first efficiency, room temperature (25°C) cycle capacity retention rate, and high temperature (45°C) cycle capacity retention rate of the battery 100 using the graphite particles show a downward trend. When the average crystallite length La of the graphite particles is too large, the orientation degree OI value of the graphite particles is high, which increases the expansion of the graphite particles during the lithium insertion process. The first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles are both low. When the average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm, the orientation degree OI value of the graphite particles can be made smaller, and the interior of the graphite particles has more orientation. When the graphite particles are applied to the battery 100, during the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate 130 in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery 100 during the charge and discharge cycle and improving the cycle capacity retention rate of the battery 100. In addition, when the average crystallite length La of the graphite particles is in the range of 35nm≤La≤55nm, the battery 100 using the graphite particles can consume less during the initial film formation in the formation stage, reducing the rupture and recombination of the solid electrolyte interface film (SEI film for short) and the consumption of active lithium during the cycle, thereby improving the cycle capacity retention rate of the battery 100.

[0104] In some embodiments, the average crystallite height Lc of the graphite particles is in the range of 30 nm ≤ Lc ≤ 45 nm.

[0105] Specifically, the average crystallite height Lc of the graphite particles can be, but is not limited to, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm, 45 nm, etc.

[0106] In this embodiment, when the average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm, the orientation degree OI value of the graphite particles can be made smaller, and the interior of the graphite particles has more orientation. The graphite particles are applied to the battery 100. During the lithium insertion process, the lithium insertion stress can be better released, and the expansion of the negative electrode plate 130 in the z-axis direction can be reduced, thereby reducing the expansion rate of the battery 100 during the charge and discharge cycle, and improving the initial efficiency and cycle capacity retention rate of the battery 100. In addition, when the average crystallite height Lc of the graphite particles is in the range of 30nm≤Lc≤45nm, the battery 100 using the graphite particles can consume less during the initial film formation in the formation stage, reducing the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, and improving the cycle capacity retention rate of the battery 100.

[0107] In some embodiments, the battery 100 satisfies the relationship: 6≤b2×(La / Lc)≤20.

[0108] Specifically, the value of b2×(La / Lc) can be but is not limited to 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc.

[0109] In this embodiment, if the value of b2×(La / Lc) is too small, then b2 is too small or (La / Lc) is too small; if b2 is too small, the vinylene carbonate in the non-free electrolyte cannot be replenished, the initial SEI stability is poor, and after the SEI film is broken, it cannot be repaired, and side reactions continue to occur to consume active lithium, thereby deteriorating the cycle life of the battery 100. When the value of b2×(La / Lc) is too large, then b2 is too large or (La / Lc) is too large; if b2 is too large, the impedance after SEI repair during the cycle will be too large, making it difficult for the negative electrode plate 130 to insert lithium, and lithium plating will easily occur, thereby worsening the cycle life of the battery 100; if (La / Lc) is too large, the orientation degree OI value of the graphite particles is high, which will increase the expansion of the graphite particles during the lithium insertion process, and reduce the initial efficiency and cycle capacity retention rate of the battery 100 using the graphite particles; in addition, since the graphite particles expand severely during the lithium insertion process, the vinylene carbonate in the non-free electrolyte can hardly ensure that the SEI film is repaired in time, and side reactions will continue to occur to consume active lithium, thereby reducing the cycle life of the battery 100. Therefore, when 6≤b2×(La / Lc)≤20, the graphite particles can have a lower orientation degree, the expansion rate can be lower during the lithium insertion process, and the non-free electrolyte can have a more suitable content of vinylene carbonate, which can repair the SEI film in time and make the SEI film have a lower impedance, thereby making the battery 100 have a longer cycle life.

[0110] In some embodiments, the graphite particles have an orientation index OI in the range of 2.1≤OI≤4.0.

[0111] It should be noted that the orientation degree OI of the graphite particles can be measured by X-ray diffractometer XRD pattern, and the OI of the graphite particles can be calculated according to the formula OI = I(004) / I(110), wherein I(004) is the intensity of the 004 diffraction peak on XRD, and I(110) is the intensity of the 110 diffraction peak on XRD.

[0112] Specifically, the orientation degree OI of the graphite particles may be, but is not limited to, 2.1, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, etc.

[0113] In this embodiment, the smaller the orientation index (OI) of the graphite particles, the smaller the expansion rate of the negative electrode plate 130 in the Z-axis direction during the lithium insertion process of the battery 100. This also helps improve the initial efficiency and cycle capacity retention of the battery 100. However, if the orientation index (OI) of the graphite particles is too small, the difficulty of preparing the graphite particles increases. As the orientation index (OI) of the graphite particles increases, the initial efficiency and cycle capacity retention of the battery 100 using the graphite particles gradually decrease. Therefore, when the orientation index (OI) of the graphite particles is within the range of 2.1 ≤ OI ≤ 4.0, the battery 100 using the graphite particles can achieve higher initial efficiency and cycle capacity retention.

[0114] In some embodiments, the graphite particles are obtained by pre-carbonizing and graphitizing a carbon source, and the carbon source includes at least one of petroleum coke and pitch coke.

[0115] Optionally, the graphite particles are prepared by the following steps: (1) crushing a carbon source to obtain precursor particles; (2) pre-treating the precursor particles at a temperature of 900°C to 1300°C to obtain intermediate particles; (3) graphitizing the intermediate particles at a temperature of 2800°C to 3100°C to obtain graphite particles.

[0116] In this embodiment, petroleum coke and pitch coke are used to prepare graphite particles. This allows the ratio La / Lc of the average crystallite length La of the prepared graphite particles to the average crystallite height Lc of the graphite particles to fall within a range of 0.8 to 1.6, thereby reducing the orientation index OI value of the graphite particles and increasing the internal orientation of the graphite particles. When used in the battery 100, the graphite particles can better release lithium insertion stress during the lithium insertion process, reduce the expansion of the negative electrode plate 130 in the z-axis direction, thereby reducing the expansion rate of the battery 100 during the charge and discharge cycle, and improving the initial efficiency and cycle capacity retention rate of the battery 100. In addition, when the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles is 0.8 to 1.6, the battery 100 using the graphite particles can also consume less during the initial film formation stage, reducing the rupture and recombination of the solid electrolyte interface film (SEI film) and the consumption of active lithium during the cycle, and improving the cycle capacity retention rate of the battery 100.

[0117] In some embodiments, the polarized structure of the carbon source includes a mosaic structure (also known as a mosaic-type structure), a block structure (also known as a block domain structure or a regional structure) and a linear structure (also known as a linear domain structure or a fiber-type structure), and the volume fraction (i.e., volume proportion) x of the mosaic structure in the polarized structure of the carbon source is in the range of: 40%≤x≤80%.

[0118] It should be noted that the polarized structure of the carbon source can be obtained by taking a polarized photograph using a polarizer with a magnification of 100 times, and the volume fractions of the mosaic structure, block structure and linear structure in the carbon source can be calculated respectively according to the area proportions of the mosaic structure, block structure and linear structure in the polarized photograph.

[0119] It can be understood that x=100%×volume of mosaic structure / (volume of mosaic structure+volume of block structure+volume of linear structure).

[0120] Specifically, the volume fraction x of the mosaic structure in the polarized structure of the carbon source can be but is not limited to 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.

[0121] In this embodiment, if the volume fraction of the mosaic structure in the polarized structure of the carbon source is too small, the orientation of the prepared graphite particles will be too large, and the expansion rate of the battery 100 using the graphite particles during the lithium insertion process will be too large, thereby reducing the first efficiency and cycle capacity retention rate of the battery 100; as the volume fraction of the mosaic structure in the polarized structure of the carbon source increases, the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles gradually increase. When the volume fraction of the mosaic structure in the polarized structure of the carbon source is too large, the requirements for the carbon source are increased, and the preparation cost of the graphite particles is increased. When the volume fraction x of the mosaic structure in the polarized structure of the carbon source is in the range of 40% ≤ x ≤ 80%, the battery 100 using the graphite particles can have a higher first efficiency and cycle capacity retention rate, and a lower preparation cost.

[0122] In some embodiments, the polarized structure of the carbon source satisfies the relationship: 1≤(x+y) / z≤4, wherein x+y+z=1, x is the volume fraction of the mosaic structure in the polarized structure of the carbon source, y is the volume fraction of the block structure in the polarized structure of the carbon source, and z is the volume fraction of the linear structure in the polarized structure of the carbon source.

[0123] Specifically, the value of (x+y) / z can be, but is not limited to, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0124] In this embodiment, if (x+y) / z is too small, the graphite particles will be too oriented, resulting in excessive expansion of the battery 100 during lithium insertion, thereby reducing the initial efficiency and cycle capacity retention of the battery 100. If (x+y) / z is too large, the carbon source requirements will increase, increasing the production cost of the graphite particles. When the polarization structure of the carbon source satisfies the relationship 1≤(x+y) / z≤4, the battery 100 using the graphite particles can achieve higher initial efficiency and cycle capacity retention, while also having lower production costs.

[0125] In some embodiments, the volume fraction y of the block structure in the polarization structure of the carbon source is in the range of 4%≤y≤16%.

[0126] Specifically, the volume fraction y of the block structure in the polarized structure of the carbon source can be, but is not limited to, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, etc.

[0127] In this embodiment, when the volume fraction y of the block structure in the polarized structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery 100 using the graphite particles during the lithium insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles. If the volume fraction y of the block structure in the polarized structure of the carbon source is too high, it will reduce the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles.

[0128] In some embodiments, the volume fraction z of the linear structure in the polarized structure of the carbon source is in the range of 15%≤z≤50%.

[0129] Specifically, the linear volume fraction z in the polarized structure of the carbon source can be but is not limited to 15%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, etc.

[0130] In this embodiment, when the volume fraction z of the linear structure in the polarized structure of the carbon source is small, it is beneficial to reduce the orientation degree of the graphite particles, reduce the expansion rate of the battery 100 using the graphite particles during the lithium insertion process, and is beneficial to improve the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles. If the volume fraction z of the linear structure in the polarized structure of the carbon source is too high, it will reduce the first efficiency and cycle capacity retention rate of the battery 100 using the graphite particles.

[0131] In some embodiments, the carbon source satisfies at least one of the following conditions:

[0132] The mass fraction of sulfur in the carbon source ranges from 0.2% to 2%;

[0133] The mass fraction of volatile matter in the carbon source ranges from 5% to 15%;

[0134] The mass fraction of ash in the carbon source is in the range of 0.1% to 1%; and

[0135] The mass fraction of water in the carbon source ranges from 3% to 9%.

[0136] Specifically, the mass fraction of sulfur in the carbon source may be, but is not limited to, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc. If the mass fraction of sulfur in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, thereby reducing the cycle performance of the battery 100 using the graphite particles.

[0137] Specifically, the mass fraction of volatile matter in the carbon source can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. If the mass fraction of volatile matter in the carbon source is too low, the porosity of the graphite particles produced will be too low, which will increase the impedance of the graphite particles, reduce the dynamic performance of the graphite particles, increase the expansion force of the graphite particles during the lithium insertion process, and reduce the cycling performance of the graphite particles. If the mass fraction of volatile matter in the carbon source is too high, the compacted density of the graphite particles produced will be reduced, and the specific capacity and energy density of the graphite particles will be reduced.

[0138] Specifically, the mass fraction of ash in the carbon source may be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. If the mass fraction of ash in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, thereby reducing the cycle performance of the battery 100 using the graphite particles.

[0139] Specifically, the mass fraction of water in the carbon source may be, but is not limited to, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc. If the mass fraction of water in the carbon source is too low or too high, the quality of the produced graphite particles will be reduced, and the cycle performance of the battery 100 using the graphite particles will be reduced.

[0140] Please see again Figure 1 and Figure 2 Optionally, the battery 100 further includes a housing 140 and an end cap assembly 150. The housing 140 and the end cap assembly 150 form a closed receiving chamber for accommodating the electrolyte, the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130. It is understood that the end cap assembly 150 electrically connects the positive electrode sheet 110 and the negative electrode sheet 130, respectively, and leads the positive electrode sheet 110 and the negative electrode sheet 130 out for electrical connection to external devices or other batteries 100.

[0141] The battery 100 of the present application is further described below through specific embodiments.

[0142] Examples 1 to 13, Comparative Examples 1 to 6

[0143] The preparation method of the battery 100 of each embodiment and comparative example includes:

[0144] (1) Preparation of the positive electrode sheet 110: The positive electrode active material sodium lithium iron phosphate, conductive carbon black (positive electrode conductive agent), and polyvinylidene fluoride (positive electrode binder) are dispersed in N-methylpyrrolidone (NMP) solvent according to a preset ratio and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector 111 aluminum foil, and the coating weight of the positive electrode slurry is 300 mg / 1540.25 mm2 After drying, cold pressing, slitting and cutting, the positive electrode sheet 110 is obtained.

[0145] (2) Preparation of negative electrode sheet 130: Graphite particles (negative electrode active material), conductive carbon black (negative electrode conductive agent), styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are dispersed in deionized water according to a preset ratio and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on the copper foil of the negative electrode current collector 131. The coating weight of the negative electrode slurry is 144 mg / 1540.25 mm 2 After drying, cold pressing, slitting and cutting, the negative electrode sheet 130 is obtained. The surface and mesopore percentages of the hard carbon of each embodiment and comparative example are shown in Table 1 below.

[0146] (3) Electrolyte preparation process: In an argon atmosphere glove box with a moisture content of less than or equal to 10 ppm, ethylene carbonate (abbreviated as EC, cyclic carbonate), ethyl methyl carbonate (EMC, chain carbonate) and diethyl carbonate (DEC, chain carbonate) are mixed in a mass ratio of 1:1:1 to form an organic solvent, dried lithium hexafluorophosphate is dissolved in the organic solvent, and different amounts of vinylene carbonate are added to obtain an electrolyte, wherein the molar concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L. The mass fractions of vinylene carbonate in the free-state electrolyte and the non-free-state electrolyte of each embodiment and comparative example are shown in Table 1 below.

[0147] (4) Preparation of the separator 120 : A 16 μm polyethylene porous film was used as the separator 120 .

[0148] (5) Assembly of battery 100: The positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly, and the electrode assembly is wound to obtain a bare cell. After welding the tabs, the bare cell is assembled into an outer package, and vacuum dried after hot pressing. Then, the liquid injection process is carried out: (1) After the first liquid injection (referred to as the first injection), packaging, standing, and formation are carried out; (2) After the second liquid injection (referred to as the second injection), high-temperature standing and capacity testing are carried out, and finally a soft-pack battery 100 with a capacity of 3.2Ah is obtained.

[0149] The following performance tests were performed on the soft pack batteries 100 prepared in each embodiment and comparative example:

[0150] (1) Average crystallite length La and average crystallite height Lc of graphite particles: X-ray diffractometer was used to measure the XRD pattern, in which a wide-angle test mode was used for phase analysis, the test range was 5° to 85°, and the rate was 10° / min. The calculation formula for the average crystallite length La of graphite particles is: La = k1λ / β1cosθ1, where k1 = 1.84, λ = 0.154nm, β1 is the diffraction peak of the 110 crystal plane stacking of graphite particles, and θ1 is the half-diffraction angle of the diffraction peak of the 110 crystal plane stacking in the XRD pattern of graphite particles. The calculation formula for the average crystallite height Lc of graphite particles is: Lc = k2λ / β2cosθ1, where k2 = 0.94, λ = 0.154nm, β2 is the diffraction peak of the 002 crystal plane stacking of graphite particles, and θ2 is the half-diffraction angle of the diffraction peak of the 002 crystal plane stacking in the XRD pattern of graphite particles.

[0151] (2) 45°C cycle capacity retention rate: The battery 100 was subjected to a charge and discharge cycle test on a charge and discharge instrument (Nebula Charge and Discharge Test System - BAT-NEEFLCT-05-V010), the test temperature was 45°C, the battery 100 was charged at a constant power of 0.5P to a charge cut-off voltage of 3.65V, the initial charge capacity was recorded, and the battery 100 was left to stand for 10 minutes, the battery 100 was discharged at a constant power of 0.5P to a discharge cut-off voltage of 2V, and the discharge capacity of the battery 100 was recorded. Wherein, P refers to the rated charge or discharge power of the battery 100, and its value is the nominal voltage U of the battery 100 multiplied by the current density of 1C, wherein the nominal voltage of the lithium iron phosphate battery 100 is 3.2V, and 0.5P refers to 0.5 times the rated power.

[0152] The capacity retention rate after the n-th cycle is calculated as follows: capacity retention rate after the n-th cycle = (discharge capacity after the n-th cycle / discharge capacity after the first cycle) × 100%.

[0153] (3) Test for the mass fraction of ethylene carbonate in the non-free electrolyte (b1): Remove the outer packaging of the battery 100, take out the electrode assembly (i.e., the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 stacked in sequence), quickly peel off the electrode assembly, place it in an aluminum-plastic bag, add a sufficient amount of acetonitrile solvent to completely immerse the electrode assembly, seal the aluminum-plastic bag containing the acetonitrile solvent and the electrode assembly, and let it stand at 35±10°C for 3 days. GC-MS is used to analyze the types and relative mass contents of ethylene carbonate and other organic components in the collected electrolyte.

[0154] (4) Test for the mass fraction of ethylene carbonate in the free electrolyte (b2): Discharge the packaged battery 100 at 0.05C to 0% SOC (2.5V). Cut a notch of approximately 0.5cm on the right side of the battery 100 facing the positive electrode column, and cut a similar notch on the right side facing the negative electrode column, ensuring that the two notches are on the diagonal line. Pour the free electrolyte into the fluoride bottle through the small opening on the positive electrode column until intermittent dripping occurs. Count for 30 seconds. Use gas chromatography-mass spectrometry (GC-MS) to test the types and relative mass contents of ethylene carbonate and other organic components in the collected electrolyte.

[0155] It should be noted that in Table 1, the mass fraction a1 of ethylene carbonate in the first injection of electrolyte refers to the mass fraction of ethylene carbonate in the electrolyte of the first injection; the mass fraction a2 of ethylene carbonate in the second injection of electrolyte refers to the mass fraction of ethylene carbonate in the electrolyte of the second injection.

[0156] The non-free electrolyte is the electrolyte adsorbed on the positive electrode sheet 110, the electrolyte adsorbed on the diaphragm 120, and the electrolyte adsorbed on the negative electrode sheet 130. After the first injection and packaging, standing, and formation, the electrolyte will be consumed after formation. Therefore, the mass fraction b1 of ethylene carbonate in the non-free electrolyte after formation will change; similarly, after the second injection, high-temperature standing, and capacity test, due to the difference in electrolyte concentration between the two injections, the components in the non-free electrolyte and the free electrolyte will diffuse, and the electrolyte will also be consumed during high-temperature standing and capacity testing. Therefore, the mass fraction b2 of ethylene carbonate in the free electrolyte will also be different from the mass fraction a2 of ethylene carbonate in the second injection of electrolyte.

[0157] The performance parameters of the battery 100 of each embodiment and comparative example are shown in Table 1 and Table 2 below.

[0158] Table 1 Performance parameters of the battery 100 of the embodiment and the comparative example

[0159]

[0160] Table 2 Performance parameters of the battery 100 of the embodiment and the comparative example

[0161]

[0162]

[0163] The test results of Examples 1 to 8, Comparative Examples 1, 2, and 3 show that when b1 / b2 is between 0.1 and 0.5, the battery 100 has a higher high-temperature (45°C) cycle capacity retention rate, and the high-temperature cycle capacity retention rate is greater than or equal to 74%. A b1 / b2 that is too small (as in Comparative Example 1) or too large (as in Comparative Example 2) will reduce the high-temperature cycle capacity retention rate of the battery 100.

[0164] It can be seen from the test results of Examples 1 to 4, Comparative Examples 1 and 2 that if the mass fraction b2 of ethylene carbonate in the free electrolyte is too high or too low, the high-temperature cycle capacity retention rate of the battery 100 will be reduced; if the mass fraction b2 of ethylene carbonate in the free electrolyte is too low, the ethylene carbonate in the non-free electrolyte cannot be replenished, the initial SEI stability is poor, and after the SEI film is broken, it cannot be repaired, and side reactions continue to occur to consume active lithium, thereby worsening the cycle life of the battery 100; if the mass fraction b2 of ethylene carbonate in the free electrolyte is too high, the impedance after SEI repair during the cycle will be too large, the negative electrode plate 130 will have difficulty in lithium insertion, and lithium plating will easily occur, thereby worsening the cycle life of the battery 100.

[0165] It can be seen from the test results of Example 2, Example 5, Example 8, Example 10, Comparative Example 4 and Comparative Example 5 that if the mass fraction b1 of ethylene carbonate in the non-free electrolyte is too high or too low, the high-temperature cycle capacity retention rate of the battery 100 will be reduced; this is because if the mass fraction b1 of ethylene carbonate in the non-free electrolyte is too low, the initial SEI formed by the battery 100 will have poor stability, and the side reactions at the interface of the negative electrode plate 130 cannot be effectively suppressed in the early stage of the cycle, which will consume active lithium, deteriorate the capacity, and thus deteriorate the cycle life; if the mass fraction b1 of ethylene carbonate in the non-free electrolyte is too high, the battery 100 will form a too thick film during the formation stage, resulting in excessive initial SEI impedance, increased polarization of the negative electrode plate 130, affecting the capacity of the battery 100, and increasing the risk of lithium plating.

[0166] From the test results of Example 5, Example 11 to Example 13 and Comparative Example 6, it can be seen that when the La / Lc of the graphite particles is small, the high-temperature cycle capacity retention rate of the battery 100 after 1000 cycles is maintained at a high level. As the La / Lc of the graphite particles increases, the high-temperature cycle capacity retention rate of the battery 100 after 1000 cycles gradually decreases. This is because when the La / Lc of the graphite particles is small, the expansion of the graphite particles in the z-axis direction can be reduced, the impact on SEI rupture is reduced, the active lithium consumption is reduced, and the cycle life is improved; as the ratio La / Lc of the average crystallite length La of the graphite particles to the average crystallite height Lc of the graphite particles increases, the orientation degree of the graphite particles gradually increases (that is, the OI value gradually increases), the first efficiency (referred to as the first effect) of the battery 100 using the graphite particles gradually decreases, and the cycle capacity retention rate of the battery 100 using the graphite particles also gradually decreases.

[0167] From the test results of Examples 1 to 13 and Comparative Examples 1 to 6, it can be seen that when b1 / b2, La / Lc, and b2×(La / Lc) are all controlled within a reasonable range, the battery 100 can have a higher cycle capacity retention rate.

[0168] See Figure 5 The embodiment of the present application further provides an energy storage device 200 , which includes a box 210 and the battery 100 described in the embodiment of the present application, and the battery 100 is accommodated in the box 210 .

[0169] The energy storage device 200 of the present application can be applied to, but is not limited to, energy storage on the power generation side, energy storage on the grid side, and energy storage on the power consumption side.

[0170] Optionally, the energy storage device 200 may include, but is not limited to, a battery module, a battery pack, a battery system, an energy storage box, an energy storage cabinet, an energy storage container, and the like. The actual application form of the energy storage device 200 provided in the embodiments of the present application may be, but is not limited to, the products listed above, and may also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 200. The drawings of the embodiments of the present application only illustrate an energy storage device 200 including multiple batteries 100, and should not be construed as limiting the energy storage device 200 of the embodiments of the present application.

[0171] Optionally, the number of batteries 100 can be but is not limited to one or more. When there are multiple batteries 100, the multiple batteries 100 are stacked in the box body 210. It can be understood that the stacking arrangement of the multiple batteries 100 can be that the multiple batteries 100 are arranged in sequence against each other, or the multiple batteries 100 can be arranged in sequence and spaced apart. In addition, the multiple batteries 100 can be stacked in the transverse direction (such as the horizontal direction) or the longitudinal direction (such as the direction of gravity). The stacking method and stacking direction of the multiple batteries 100 can be designed according to actual conditions, and this application does not impose specific restrictions.

[0172] The term "plurality" means greater than or equal to two.

[0173] It can be understood that the multiple batteries 100 of the energy storage device 200 can be connected in parallel with each other; or in series with each other; or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple batteries 100 of the same energy storage device 200.

[0174] It is understood that the housing 210 has a receiving cavity, and one or more batteries 100 are received in the receiving cavity. In some embodiments, each receiving cavity receives one battery 100. In other embodiments, each receiving cavity receives multiple batteries 100.

[0175] See Figure 6 and Figure 7 , an embodiment of the present application also provides an energy storage system 300, which includes the energy storage device 200 described in the embodiment of the present application; and an electric energy conversion device 310, the electric energy conversion device 310 is electrically connected to the energy storage device 200, the electric energy conversion device 310 is used to convert other forms of energy into electric energy, and the energy storage device 200 is used to store the electric energy.

[0176] It should be noted that energy storage (i.e., energy storage) has a wide range of application scenarios, including power generation-side energy storage, grid-side energy storage, and power consumption-side energy storage. The energy storage system 300 of the embodiment of the present application is described in detail using power generation-side energy storage as an example. This description should not be construed as limiting the energy storage system 300 of the embodiment of the present application, nor should it be construed as limiting the energy storage device 200 and battery 100 of the embodiment of the present application.

[0177] During operation, the power conversion device 310 converts other forms of energy into electrical energy and stores it in the energy storage device 200. This stored energy can be used to supply loads such as streetlights and household appliances during peak electricity prices, or to provide power during power outages. The electricity generated by the power conversion device 310 can also be supplied to the grid via high-voltage cables to alleviate pressure on the grid during peak hours.

[0178] Optionally, the electric energy conversion device 310 can convert at least one other form of energy such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0179] Optionally, the number of the electric energy conversion devices 310 may be one or more. When there are multiple electric energy conversion devices 310, the multiple electric energy conversion devices 310 may be connected in series, in parallel, or in mixed connection, which is not specifically limited in this application.

[0180] Optionally, the electric energy conversion device 310 may be, but is not limited to, at least one of a photovoltaic panel, a wind power generation device, a hydropower generation device, and the like.

[0181] Optionally, the number of the energy storage devices 200 may be one or more. When the number of the energy storage devices 200 is multiple, the multiple energy storage devices 200 are connected in series or in parallel, which is not specifically limited in this application.

[0182] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of this application, unless there is a contradiction between them.

[0183] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A battery, characterized in that: The battery includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte; the electrolyte includes a non-free electrolyte and a free electrolyte, the free electrolyte and the non-free electrolyte both include vinylene carbonate, the mass fraction of vinylene carbonate in the non-free electrolyte is b1, and the unit is %; the mass fraction of vinylene carbonate in the free electrolyte is b2, then the battery is charged and discharged at 25°C and 0.5P, when the cycle capacity retention rate is greater than or equal to 99.5%, the electrolyte satisfies 0.1≤b1 / b2≤0.5; wherein, the non-free electrolyte includes the electrolyte adsorbed on the positive electrode sheet, the electrolyte adsorbed on the separator and the electrolyte adsorbed on the negative electrode sheet.

2. The battery according to claim 1, characterized in that When the battery is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b1 of vinylene carbonate in the non-free electrolyte is in the range of 0.5%≤b1%≤4%.

3. The battery according to claim 1, characterized in that When the battery is charged and discharged at 0.5P at 25°C and the cycle capacity retention rate is greater than or equal to 99.5%, the mass fraction b2 of vinylene carbonate in the free electrolyte is in the range of 3%≤b2%≤9%.

4. The battery according to claim 1, characterized in that The electrolyte includes an organic solvent, which includes a cyclic carbonate and a chain carbonate. The organic solvent includes 50% to 80% of the chain carbonate and 20% to 50% of the cyclic carbonate by mass.

5. The battery according to claim 1, characterized in that The negative electrode active material includes graphite particles, and the graphite particles satisfy the following relationship: 0.8≤La / Lc≤1.6, wherein La is the average crystallite length of the graphite particles, and Lc is the average crystallite height of the graphite particles.

6. The battery according to claim 5, characterized in that The range of the average crystallite length La of the graphite particles is: 35nm≤La≤55nm.

7. The battery according to claim 5, characterized in that The range of the average crystallite height Lc of the graphite particles is: 30nm≤Lc≤45nm.

8. The battery according to claim 5, characterized in that The battery satisfies the relationship: 4≤b2×(La / Lc)≤10.

9. An energy storage device, characterized in that: include: Box; as well as The battery according to any one of claims 1 to 8, wherein the battery is housed in the box.

10. An energy storage system, characterized in that: include: The energy storage device according to claim 9; as well as An electric energy conversion device, the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

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