Lithium ion battery, battery pack, and electric device

Abstract

A lithium ion battery, a battery pack, and an electric device. The lithium ion battery comprises: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer comprises a first active material and a second active material of different types, and the second active material is a lithium-rich material; the electrolyte comprises a lithium salt, a solvent and an additive, and the additive comprises a cyclic organic sulfide containing a sulfur-oxygen double bond; and the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprises a third active material, and the lithium ion battery satisfies: 0<10×n×w×(6×a-n)≤2. The lithium ion battery can solve the impact of the lithium-rich material on safety performance, prolong the cycle service life of the battery, and improve the cycle performance effect of the battery.

Description

Lithium-ion battery, battery pack, and power-consuming device

[0001] Related cross-references

[0002] This disclosure claims priority to Chinese patent application number 2023111523505, filed with the Patent Office of China on September 7, 2023, entitled “A lithium-ion battery, battery pack and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a lithium-ion battery, a battery pack, and an electrical device. Background Art

[0004] For lithium-ion batteries, in order to reduce capacity decay in the initial stage of use and extend the cycle life of the battery, the use of lithium-rich active materials in the positive electrode of the lithium-ion battery to supplement the consumption of lithium ions has become a popular research measure.

[0005] However, lithium-rich materials currently produce highly reactive high-valent transition metals during the use of lithium-ion batteries, which may also lead to transition metal dissolution, increasing the risk of battery safety testing and causing the battery to experience a sharp decline in life in the later stages of the cycle. At the same time, under high-rate charging conditions, the addition of lithium-rich materials will also increase the risk of lithium plating at the battery's negative electrode.

[0006] Summary of the Invention

[0007] The embodiments of the present application disclose a lithium-ion battery, a battery pack, and an electrical device to address the impact of lithium-rich materials on safety performance in the prior art, increase the cycle life of the battery, and improve the cycle performance of the battery.

[0008] In a first aspect, an embodiment of the present application provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet to form an electrode assembly, and the electrolyte at least partially infiltrates the electrode assembly;

[0009] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a first active material and a second active material of different types, wherein the second active material is a lithium-rich material; the electrolyte includes a lithium salt, a solvent and an additive, and the additive includes a cyclic organic sulfide containing a sulfur-oxygen double bond; the negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a third active material;

[0010] The lithium-ion battery satisfies the following relationship: 0<10×n×w×(6×an)≤2;

[0011] Wherein, n is the mass percentage of the second active material in the positive electrode active material layer;

[0012] The w is the ratio of the positive electrode active material layer density to the negative electrode active material layer density;

[0013] The a is the mass percentage of the cyclic organic sulfide containing sulfur-oxygen double bonds in the electrolyte.

[0014] In a second aspect, an embodiment of the present application provides a battery pack, comprising a box and a lithium-ion battery as described in the first aspect placed in the box.

[0015] In a third aspect, an embodiment of the present application provides an electrical device, which includes an electrical device body and a lithium-ion battery as described in the first aspect disposed in the electrical device body.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The embodiment of the present application provides a lithium-ion battery. By arranging a second active material having a first active material and a lithium-rich material type in the positive electrode sheet, the first active material can be used as the main active material to participate in the electrochemical reaction while the high lithium content in the lithium-rich material can be used to supplement the active lithium source, thereby reducing the active lithium source that is irreversibly consumed due to the formation and continuous growth of the interfacial passivation film of the negative electrode sheet during the battery formation and cycle stages, thereby reducing the battery life attenuation amplitude and improving the battery life from the perspective of providing more active lithium sources. As for the risk of negative electrode lithium plating caused by the use of lithium-rich materials with highly reactive transition metal elements as the second active material, and a series of problems such as the dissolution of high-valent metals or deposition at the interface of the negative electrode sheet, amplification of electrolyte side reactions, and the resulting impact on battery safety performance and cycle life, the present application has found that by using a cyclic organic sulfide containing a sulfur-oxygen double bond as an additive in the electrolyte, and exploring the amount of the above additives, positive and negative active materials, and lithium-rich materials to satisfy a specific relationship, the above problems can be well solved.

[0018] First, for hybrid positive electrode active materials using lithium-rich materials, when the interfacial passivation film of the positive electrode plate is unstable during use, there is a risk of transition metal dissolution or deposition at the interface of the negative electrode plate, and increased side reactions in the electrolyte. A cyclic organic sulfide containing a sulfur-oxygen double bond is provided in the electrolyte as an additive. Such compounds can react at the positive and negative electrode plates earlier than the solvent in the electrolyte to form a stable interfacial passivation film, thereby reducing the contact between the positive and negative electrode plates and the electrolyte, thereby inhibiting the dissolution of transition metals or precipitation at the interface of the negative electrode plate, reducing the impact of the addition of a second active material such as a lithium-rich material on the battery safety performance, and improving the battery cycle life.

[0019] Secondly, in order to solve the problem of lithium plating in the negative electrode sheet caused by insufficient lithium storage space in the negative electrode active material layer during the use of lithium-rich materials, the surface density of the negative electrode active material layer is increased, thereby increasing the lithium storage space of the negative electrode third active material, thereby improving the battery cycle effect.

[0020] Finally, when the mass percentage n of the second active material in the positive electrode active material layer, the ratio w of the positive electrode active material surface density to the negative electrode active material surface density, and the mass percentage a of the cyclic organic sulfide containing a sulfur-oxygen double bond in the electrolyte satisfy the relationship 0 < 10 × n × w × (6 × an) ≤ 2, the second active material can play the role of reducing the battery life attenuation and improving the battery life, while controlling the impact of lithium-rich materials on the negative electrode sheet lithium plating, metal dissolution caused by the instability of the positive electrode sheet interface passivation film, or deposition on the negative electrode interface, etc. on the battery safety and cycle performance, thereby reducing the adverse effects of the use of the second active material on battery performance. Among them, when n is too high, the relationship can be controlled to meet the above range by reducing w and increasing a, and vice versa. In this way, when n is too high and negative electrode lithium plating may occur, by reducing w, that is, increasing the surface density of the negative electrode active material layer, more lithium storage space is reserved, reducing negative electrode sheet lithium plating. In addition, when n is too high and may cause safety risks to the battery, the safety issues of lithium-rich materials can be improved by increasing a, that is, adjusting the amount of cyclic organic sulfide additives containing sulfur-oxygen double bonds in the electrolyte to oxidize and decompose at the interface of the positive and negative electrodes to form a stable interface passivation film.

[0021] That is to say, when the relationship 0<10×n×w×(6×an)≤2 is satisfied, on the one hand, by adjusting n and a, the phenomenon of metal dissolution or deposition on the surface of the negative electrode sheet caused by the instability of the interfacial passivation film of the positive electrode during the use of lithium-rich materials can be reduced, which is beneficial to reducing the safety risk of the battery and improving the cycle life of the battery; on the other hand, by adjusting n and w, the problem of lithium plating on the negative electrode sheet caused by the limited lithium storage space of the third active material of the negative electrode can be alleviated, which helps to increase the recycling effect of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, a brief introduction will be given below to 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 any creative work.

[0023] FIG1 is a voltage change curve of the lithium-ion batteries of Example 4, Comparative Example 1, and Comparative Example 4 of the present application during an overcharge test;

[0024] FIG2 is a diagram showing the discharge capacity retention rates of the lithium-ion batteries of Comparative Examples 1 and 4 of the present application;

[0025] FIG3 is an XRD test diagram of the positive electrode sheet used in Example 1 of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0027] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0028] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0029] Furthermore, the terms "installed," "disposed," "provided with," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integral structures; mechanical connections or electrical connections; direct connections, indirect connections through an intermediary, or internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0030] Furthermore, the terms "first," "second," etc., are primarily used to distinguish between different devices, elements, or components (which may or may not be of the same type and configuration), and are not intended to indicate or imply the relative importance or quantity of the devices, elements, or components indicated. Unless otherwise specified, "plurality" means two or more.

[0031] The technical solution provided in this application will be further described below with reference to the embodiments and drawings.

[0032] During the formation and cycling of lithium-ion batteries, the electrolyte decomposes at the electrode interface to form an interfacial passivation film. The formation of the interfacial passivation film will continuously consume the active lithium source, thereby reducing the battery's initial coulombic efficiency, battery capacity and energy density.

[0033] Therefore, in order to compensate for the attenuation of battery energy density caused by the consumption of active lithium sources, lithium-rich materials are added to the positive electrode active material layer to supplement the loss of active lithium sources. However, the use of lithium-rich materials will cause some problems. First, when the interfacial passivation film of the positive electrode is unstable, it will promote the occurrence of oxidation side reactions in the positive electrode, thereby causing the dissolution of transition metals, amplifying the occurrence of side reactions in the electrolyte, and causing safety problems when the battery is overcharged; secondly, transition metals enter the electrolyte in the form of ions, are reduced and precipitated at the negative electrode interface, destroying the stability of the interfacial passivation film of the negative electrode, and thus affecting the safety performance of the battery; finally, under high-rate charging conditions, when lithium ions are deintercalated from the positive electrode, if the lithium storage space of the negative electrode active material layer is limited, the lithium ions gain electrons on the negative electrode surface to form lithium elements, resulting in lithium precipitation, which affects the use of the battery and is not conducive to improving the electrochemical performance of the battery. The introduction of cyclic organic sulfides containing sulfur-oxygen double bonds helps to form a stable interfacial passivation film on the positive and negative electrode sheets, thereby improving the phenomenon of transition metal dissolution or deposition at the interface of the negative electrode sheet. If there is no lithium-rich material and only additives, the thickness of the interfacial passivation film of the negative electrode sheet increases, the battery impedance increases, and thus affects the electrochemical performance of the battery. Therefore, the present application comprehensively sets the relationship between the ratio w of the surface density of the positive electrode active material layer to the surface density of the negative electrode active material layer, the mass percentage a of the cyclic organic sulfide containing sulfur-oxygen double bonds in the electrolyte, and the mass percentage n of the lithium-rich material in the positive electrode active material layer, and obtains the relationship of 0<10×n×w×(6×an)≤2. If these three parameters are controlled within this range, the lithium-rich material can fully play its role, and the problems caused by the use of lithium-rich materials can be further solved.

[0034] In a first aspect, the present invention provides a lithium-ion battery:

[0035] The lithium-ion battery comprises: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the separator is provided between the positive electrode sheet and the negative electrode sheet to form an electrode assembly, and the electrolyte at least partially soaks the electrode assembly;

[0036] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a first active material and a second active material of different types, wherein the second active material is a lithium-rich material; the electrolyte includes a lithium salt, a solvent and an additive, and the additive includes a cyclic organic sulfide containing a sulfur-oxygen double bond; the negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a third active material;

[0037] The lithium-ion battery satisfies the following relationship: 0<10×n×w×(6×an)≤2;

[0038] Wherein, n is the mass percentage of the second active material in the positive electrode active material layer;

[0039] The w is the ratio of the positive electrode active material layer density to the negative electrode active material layer density;

[0040] The a is the mass percentage of the cyclic organic sulfide containing sulfur-oxygen double bonds in the electrolyte.

[0041] On the one hand, to improve the stability of the interfacial passivation film between the positive and negative electrode sheets, a cyclic organic sulfide containing a sulfur-oxygen double bond is added to the electrolyte as an additive. This additive undergoes redox polymerization at the positive and negative electrode sheets, helping to form a stable interfacial passivation film on the positive and negative electrode sheets, thereby reducing the impact of the addition of lithium-rich materials on battery safety and improving battery cycle performance. On the other hand, to improve the lithium plating phenomenon on the negative electrode sheet, the surface density of the negative electrode active material layer is adjusted, thereby reserving more lithium storage space in the negative electrode active material layer to alleviate the problem of lithium plating on the negative electrode sheet.

[0042] The relationship proposed in this application, when n, w, and a satisfy the above relationship, can solve the safety and lithium plating problems, thereby increasing the electrochemical performance of the battery. When n increases and the negative electrode plate has a lithium plating problem, this problem can be alleviated by reducing w to increase the negative electrode lithium storage space; when the transition metal dissolves or precipitates at the interface of the negative electrode plate, it can be alleviated by increasing a to form a stable interface passivation film on the positive and negative electrode plates, and vice versa. In other words, when the above relationship can be satisfied, the effects of lithium-rich materials can be exerted while further alleviating the problems caused by lithium-rich materials, thereby improving the safety performance and cycle life of the battery.

[0043] Illustratively, the relationship 10×n×w×(6×an) can satisfy any value within the above numerical range, for example, 10×n×w×(6×an) is 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2.

[0044] Furthermore, the positive electrode active material layer density is w1, the negative electrode active material layer density is w2, w is the ratio of w1 to w2, and w satisfies: 1.5≤w≤3.

[0045] When w is within the above range, the lithium storage space of the negative electrode active material layer can be better matched with the amount of active lithium source provided by the positive electrode. This can not only avoid the risk of lithium plating at the negative electrode due to the surface density of the positive electrode active material layer being too high and the surface density of the negative electrode active material layer being too low due to w being too large during the charging process, which results in limited lithium storage space in the negative electrode active material layer; it can also avoid the risk of excessive lithium storage space in the negative electrode active material layer due to w being too small, which affects the battery charge and discharge efficiency and capacity, and causes unnecessary waste. For example, the value of w is 1.5, 1.8, 1.9, 2, 2.2, 2.4, 2.6, 2.8, 3, etc.

[0046] It is understood that the positive electrode active material layer density refers to the ratio of the positive electrode coating slurry to the current collector area, and the negative electrode active material layer density refers to the ratio of the negative electrode coating slurry to the current collector area.

[0047] Furthermore, the w1 satisfies: 0.1 mg / mm 2 ≤w1≤0.3mg / mm 2 , the w2 satisfies: 0.05mg / mm 2 ≤w2≤0.2mg / mm 2 .

[0048] When w1 is within this range, the first active material and the second active material can provide a suitable amount of active lithium source. When w2 is within this range, the negative electrode active material layer can provide sufficient lithium storage space. When w1 and w2 are lower than this range, the content of active lithium source provided by the positive electrode active material layer is limited, and the lithium storage space of the negative electrode active material layer is limited. When w1 and w2 are higher than this range, the content of positive and negative electrode active materials is too high and easy to fall off, react with the electrolyte, amplify the occurrence of electrolyte side reactions, and thus have an adverse effect on the electrochemical performance of the battery. For example, w1 is 0.1mg / mm 2 , 0.12mg / mm 2 , 0.15mg / mm 2 , 0.18mg / mm 2 , 0.2mg / mm 2 , 0.24mg / mm 2 , 0.26mg / mm 2 , 0.28mg / mm 2 , 0.3mg / mm 2 etc. w2 is 0.05mg / mm 2 , 0.07mg / mm 2 , 0.1mg / mm 2 , 0.12mg / mm 2 , 0.14mg / mm 2 , 0.16mg / mm 2, 0.18mg / mm 2 , 0.2mg / mm 2 wait.

[0049] Furthermore, the n satisfies: 0.5%≤n≤15%.

[0050] When n is within the above range, the beneficial effects of lithium-rich materials can be fully utilized. If the n value is too large, the lithium-rich material content is too high, the stability of the positive electrode interface passivation film is insufficient, the lithium-rich material reacts with the electrolyte, and the transition metal is eluted, amplifying the side reactions between the positive electrode and the electrolyte; in addition, the transition metal enters the electrolyte and precipitates at the negative electrode interface, thereby destroying the stability of the negative electrode interface passivation film, amplifying the side reactions between the negative electrode and the electrolyte, and thus reducing the safety performance of the battery. At the same time, if the n value is too large, the active lithium source content is high. If the lithium storage space of the negative electrode active material layer is limited, the negative electrode will be at risk of lithium plating. If the n value is too small, the lithium-rich material cannot provide sufficient active lithium source, thereby reducing the battery's first-cycle coulombic efficiency and battery capacity. For example, the value of n is 0.5%, 1.0%, 2%, 2.5%, 5%, 6%, 7%, 8%, 8.5%, 9%, 10%, 12%, 13%, 14.5%, 15%, etc.

[0051] Furthermore, the a satisfies: 0.1%≤a≤10%.

[0052] If the value of a is within this range, the cyclic organic sulfide containing a sulfur-oxygen double bond can act on the interface between the positive and negative electrode sheets, which is conducive to forming a stable and appropriately thick interfacial passivation film on the positive and negative electrode sheets. This avoids the situation where the passivation film becomes thicker and the battery impedance increases when the value of a is too large, which in turn causes a decline in battery performance. It also avoids the situation where the cyclic organic sulfide containing a sulfur-oxygen double bond has difficulty acting on the positive and negative electrode sheets. In this case, if the interfacial passivation film has poor stability, it will aggravate the occurrence of electrolyte side reactions, increase the probability of safety risks, and reduce the cycle life of the battery.

[0053] Illustratively, the value of a is 0.1%, 1.0%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 5.5%, 6%, 7%, 8%, 9%, 10%, etc.

[0054] Furthermore, the first active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide or lithium nickel cobalt manganese oxide; and / or,

[0055] The second active material comprises at least one of lithium-rich manganese-based, lithium-rich nickel-based, lithium-rich nickel-cobalt-manganese-based or lithium oxide; and / or,

[0056] The additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, 4-methyl vinyl sulfate, 1,3-propylene glycol cyclic sulfate, ethylene sulfite, methylene dimethylsulfonate, 1,4-butane sultone, and 2,4-butane sultone.

[0057] The selection of the first active material determines some key indicators of the battery, such as energy density, charge and discharge rate, and safety. Based on the selection of the first active material, the lithium-rich material is used as the second active material, which can continuously release active lithium sources during the battery cycle and formation process, improve the battery capacity decay caused by the consumption of active lithium sources, and increase the service life of the lithium-ion battery. For example, the first active material is lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese phosphate, lithium manganese phosphate and lithium manganese oxide, lithium manganese iron phosphate and lithium iron phosphate, lithium nickel oxide, lithium cobalt oxide and lithium nickel cobalt manganese oxide, or lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide and nickel cobalt manganese oxide, etc.; the second active material is lithium-rich manganese-based, lithium-rich nickel-based, lithium-rich nickel cobalt manganese and lithium-rich nickel-based, lithium-rich nickel cobalt manganese, lithium-rich nickel-based and lithium oxide, etc.

[0058] Cyclic organic sulfides containing sulfur-oxygen double bonds are selected as electrolyte additives because they can form a stable interfacial passivation film at the positive electrode, preventing the dissolution of transition metals or their deposition on the negative electrode, which can lead to amplification of electrolyte side reactions and increase battery safety risks and reduce the battery's cycle life. Examples of cyclic organic sulfides containing sulfur-oxygen double bonds include 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, 2,4-butane sultone, vinyl sulfate, ethylene sulfite, and methylene disulfonate.

[0059] Furthermore, the solvent in the electrolyte includes cyclic carbonate, the mass percentage of the cyclic carbonate in the electrolyte is t2, and t2 and a satisfy: 1≤(t2-0.2) / a≤5.

[0060] When the above relationship holds true, the matching degree between the cyclic organic sulfide containing a sulfur-oxygen double bond and the cyclic carbonate can be optimized, and the performance of the interfacial passivation film is better. This is because the inorganic component content in the cyclic organic sulfide containing a sulfur-oxygen double bond is high, and the interfacial passivation film formed is relatively rigid but has poor flexibility. When faced with volume changes during battery charging and discharging, the risk of rupture of the interfacial passivation film of the negative electrode plate is increased, causing the negative electrode active material layer to contact the electrolyte, thereby adversely affecting battery performance; while cyclic carbonates have good flexibility and can form flexible components in the interfacial passivation film, changing the flexibility of the interfacial passivation film, thereby making the interfacial passivation film of the electrode plate have better performance. If the relationship does not hold true, the flexibility or rigidity of the negative electrode passivation film is poor, which is not conducive to coping with changes in battery volume during charging and discharging, thereby affecting the service life of the battery. For example, the value of (t2-0.2) / a is 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc.

[0061] Furthermore, the t2 satisfies 20% <t2≤60%。

[0062] When t2 satisfies the above relationship, the negative electrode passivation film has good flexibility and rigidity. When t2 is too high, the interface passivation film of the negative electrode plate has strong flexibility and weak rigidity. When t2 is too small, the interface passivation film of the negative electrode plate has weak flexibility and strong rigidity. Both types of interface passivation films are difficult to cope with the changes in battery volume during charging and discharging, which has a negative impact on the electrochemical performance and safety performance of the battery. For example, the value of n is 20%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 53%, 55%, 57%, 60%, etc.

[0063] Furthermore, the cyclic carbonate includes but is not limited to at least one of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, and vinylethylene carbonate.

[0064] Cyclic carbonates have high dielectric constants and ionic conductivity, and they can also form a flexible component in the interfacial passivation film of the negative electrode. This optimizes the performance of the interfacial passivation film, allowing it to cope with volume changes during battery charge and discharge, further improving the battery's electrochemical performance. Examples of cyclic carbonates include ethylene carbonate, fluoroethylene carbonate, vinylene carbonate and fluoroethylene carbonate, vinyl ethylene carbonate, ethylene carbonate, and fluoroethylene carbonate.

[0065] In a second aspect, an embodiment of the present application provides a battery pack, comprising a box and a lithium-ion battery as described in the first aspect placed in the box.

[0066] Multiple lithium-ion batteries are placed in series or in parallel in a battery pack box, and the battery pack has a protective effect on the lithium-ion batteries.

[0067] In a third aspect, an embodiment of the present application provides an electrical device, which includes an electrical device body and a lithium-ion battery as described in the first aspect disposed in the electrical device body.

[0068] The lithium-ion battery is used to provide power to an electrical device. The electrical device includes a positive electrode and a negative electrode. The negative electrode of the lithium-ion battery is connected to the negative electrode of the device, and the positive electrode of the lithium-ion battery is connected to the negative electrode of the device.

[0069] The technical solution of the present application will be further explained below in conjunction with more specific embodiments and experimental test results.

[0070] Example 1

[0071] This embodiment provides a lithium-ion battery, which includes: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The separator is provided between the positive electrode sheet and the negative electrode sheet to form an electrode assembly. The electrolyte at least partially soaks the electrode assembly.

[0072] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer includes a first active material and a second active material of different types, wherein the second active material is a lithium-rich nickel-based electrolyte; the electrolyte includes a lithium salt, a solvent and an additive, wherein the additive includes methylene disulfonate; the negative electrode includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes graphite;

[0073] Lithium-ion batteries satisfy the following relationship:

[0074] n is 0.5%, a is 0.1%, w is 3, and the relationship is 10×0.5%×3×(6×0.1%-0.5%)=0.00015.

[0075] Wherein, n is the mass percentage of lithium-rich nickel in the positive electrode active material layer;

[0076] w is the ratio of the surface density of the positive electrode active material layer to the surface density of the negative electrode active material layer;

[0077] a is the mass percentage of methylene disulfonate in the electrolyte.

[0078] This embodiment also provides a method for preparing the above-mentioned lithium-ion battery, which comprises the following steps:

[0079] Preparation of positive electrode sheet: lithium iron phosphate, lithium-rich nickel base, conductive carbon black, and polyvinylidene chloride are dispersed in N-methylpyrrolidone at a mass ratio of 95:2.5:1:1.5 and mixed evenly to obtain positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector. The positive electrode active material layer density w1 is 0.165 mg / mm 2 ; After drying, cold pressing, slitting, cutting and other processes, the positive electrode sheet is obtained.

[0080] Preparation of negative electrode sheet: Graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are dispersed in a solvent in a mass ratio of 96:1.5:1.5:1 and mixed evenly to obtain negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector. The density of the negative electrode active material layer is w2, which is 0.055 mg / mm 2 After drying, cold pressing, slitting and cutting, the negative electrode sheet is obtained.

[0081] Preparation of electrolyte: In an argon atmosphere glove box with a moisture content of ≤1 ppm, dry lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide were dissolved in 20% ethylene carbonate and stirred until completely dissolved. Finally, 0.1% methylene disulfonate was added and mixed uniformly to obtain an electrolyte.

[0082] Preparation of isolation film: 12 micron polyethylene film was selected.

[0083] Assembly of lithium-ion batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order so that the separator is in the middle of the positive and negative electrodes to separate the positive and negative electrodes. After winding, a bare cell is obtained. After connecting the tabs, the cell is assembled into an outer package. After injecting the prepared electrolyte, the cell is packaged, allowed to stand, formed, shaped, and capacity tested, and finally a lithium-ion battery is prepared.

[0084] Example 2:

[0085] The difference between this embodiment and the first embodiment is: a.

[0086] Example 3:

[0087] The differences between this embodiment and the first embodiment are: a and t2.

[0088] Example 4:

[0089] The differences between this embodiment and the first embodiment are: n, a, w2, and w.

[0090] Embodiment 5:

[0091] The differences between this embodiment and the first embodiment are: n, a, w2, w, the type of cyclic carbonate, and t2.

[0092] Example 6:

[0093] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, the type of cyclic carbonate, and t2.

[0094] Embodiment seven:

[0095] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, the type of cyclic carbonate, and t2.

[0096] Embodiment 8:

[0097] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, the type of cyclic carbonate, and t2.

[0098] Embodiment 9:

[0099] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, and the type of cyclic carbonate.

[0100] Embodiment 10:

[0101] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0102] Example 11:

[0103] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0104] Example 12:

[0105] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0106] Example 13:

[0107] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0108] Example 14:

[0109] The differences between this embodiment and the first embodiment are: n, a, w, t2, and the type of additive.

[0110] Embodiment 15:

[0111] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0112] Example 16:

[0113] The differences between this embodiment and the first embodiment are: n, a, w, the type of cyclic carbonate, t2, and the type of additive.

[0114] Embodiment 17:

[0115] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0116] Embodiment 18:

[0117] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, and the type of additive.

[0118] Embodiment 19:

[0119] The differences between this embodiment and the first embodiment are: n, a, w, w2, the type of cyclic carbonate, t2, and the type of additive.

[0120] Embodiment 20:

[0121] The differences between this embodiment and the first embodiment are: n, a, w, w2, and t2.

[0122] Embodiment 21:

[0123] The differences between this embodiment and the first embodiment are: n, a, w, w2, and t2.

[0124] Embodiment 22:

[0125] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, and the type of cyclic carbonate.

[0126] Embodiment 23:

[0127] The differences between this embodiment and the first embodiment are: n, a, w, w2, and the type of additive.

[0128] Example 24:

[0129] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, the type of cyclic carbonate, and the type of additive.

[0130] Embodiment 25:

[0131] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, the type of cyclic carbonate, and the type of additive.

[0132] Example 26:

[0133] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, the type of cyclic carbonate, and the type of additive.

[0134] Embodiment 27:

[0135] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, and the type of additive.

[0136] Embodiment 28:

[0137] The differences between this embodiment and the first embodiment are: n, a, w, t2, w2, and the type of additive.

[0138] Embodiment 29:

[0139] The differences between this embodiment and the first embodiment are: n, a, w, t2, w1, w2, and the type of additive.

[0140] Embodiment 30:

[0141] The differences between this embodiment and the first embodiment are: n, a, w, t2, w1, w2, and the type of additive.

[0142] Embodiment 31:

[0143] The differences between this embodiment and the first embodiment are: n, a, w, t2, w1, w2, and the type of additive.

[0144] Embodiment 32:

[0145] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, and the type of the second active material.

[0146] Embodiment 33:

[0147] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, the type of cyclic carbonate, and the type of the second active material.

[0148] Embodiment 34:

[0149] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, the type of cyclic carbonate, and the type of the second active material.

[0150] Embodiment 35:

[0151] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, and the type of the second active material.

[0152] Embodiment 36:

[0153] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, the type of cyclic carbonate, the type of the second active material, and the type of additive.

[0154] Embodiment 37:

[0155] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, the type of the second active substance, and the type of additives.

[0156] Embodiment 38:

[0157] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, and the type of the second active material.

[0158] Embodiment 39:

[0159] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, and the type of the second active material.

[0160] Embodiment 40:

[0161] The differences between this embodiment and the first embodiment are: n, a, w, w1, w2, t2, the type of the second active substance, and the type of additives.

[0162] Comparative Example 1:

[0163] The differences between this comparative example and Example 1 are: n, a, no second active substance, and no additives.

[0164] Comparative Example 2:

[0165] The difference between this comparative example and Example 1 is: n, a, no second active substance.

[0166] Comparative Example 3:

[0167] The difference between this comparative example and Example 1 is: a. no additive.

[0168] Comparative Example 4:

[0169] The difference between this comparative example and Example 1 is: n, a, no additive.

[0170] Comparative Example 5:

[0171] The differences between this comparative example and Example 1 are: n, a, w, w2, and no additive.

[0172] Comparative Example 6:

[0173] The differences between this comparative example and Example 1 are: n, a, w, w2, and no additive.

[0174] Comparative Example 7:

[0175] The differences between this comparative example and Example 1 are: n, a, w, and w2.

[0176] The details of the experimental parameter changes of Examples 1 to 34 and Comparative Examples 1 to 7 are shown in Table 1.

[0177] Table 1 Summary of components and parameters of Examples and Comparative Examples

[0178] Test data 1:

[0179] 1. Overcharge test and safety level assessment

[0180] 1.1 Pretreatment: At 25°C, the prepared lithium-ion battery was first allowed to stand for 5 hours; then discharged at a rate of 0.5P to 2.5V, and then allowed to stand for 30 minutes; and then charged at a rate of 0.5P to 3.65V, completing the pretreatment.

[0181] 1.2 Overcharge test: At 25°C, after the pre-treated lithium-ion battery has been left to stand for 30 minutes, it is first charged at a constant current rate of 1C until the battery voltage rises to 5.475V or the constant current charging time reaches 1 hour. After either of the above conditions is met, charging is stopped and the battery voltage, temperature and other parameters are continuously observed. The overcharge test is completed after 1 hour of observation.

[0182] 1.3 Safety Level Assessment: Based on the performance of lithium-ion batteries in overcharge tests, they are divided into four safety levels, with level 1 being the best and level 4 being the worst. The specific evaluation criteria are: if the battery catches fire or explodes during the overcharge test, the safety level is level 4; if the battery does not catch fire or explode during the overcharge test, but thermal runaway occurs after charging is stopped (the test object voltage is ≤ 1.0V and the temperature monitoring sampling frequency is 1s, and the temperature rise rate of the monitoring point is ≥ 5℃ / s for three consecutive times), the safety level is level 3; if the battery does not catch fire or explode during the overcharge test, and thermal runaway does not occur after charging is stopped, but the battery's safety valve opens or the battery deflates, the safety level is level 2; if the battery does not catch fire or explode during the overcharge test, and thermal runaway does not occur after charging is stopped, and the battery's safety valve does not open or the battery deflates, the safety level is level 1.

[0183] 2. Cycle performance test

[0184] 2.1 At 25°C, the prepared lithium-ion battery was left to stand for 1 hour, then charged to 3.65V at a rate of 1P and left to stand for 10 minutes; then discharged to 2.5V at a rate of 1P and left to stand for 10 minutes.

[0185] 2.2 At 25°C, after resting the lithium-ion battery from 2.1 for 1 hour, charge it at a rate of 1P to 3.65V, then let it rest for 10 minutes. Then discharge it at a rate of 1P to 2.5V, then let it rest for 10 minutes. Record the discharge capacity as the initial capacity.

[0186] Among them, P refers to the rated charge or discharge power of the battery, and its value is the battery's nominal voltage U multiplied by the current density of 1C. The nominal voltage of the iron phosphate battery is 3.2V, and 1P refers to 1 times the rated power.

[0187] 2.3 At 25°C, charge the lithium-ion battery described in 2.1 at a charge rate of 1P to 3.65V, then allow it to rest for 10 minutes. Then, discharge it at a charge rate of 1P to 2.5V, then allow it to rest for 10 minutes. Perform a cycling performance test under these charge and discharge conditions. Record the capacity retention relative to the initial capacity after 3000 and 8000 charge and discharge cycles.

[0188] 3. Negative electrode lithium deposition test

[0189] At 25°C, the prepared lithium-ion battery was left to rest for 1 hour, then charged at a 1P rate to 3.65V and left to rest for 10 minutes. It was then discharged at a 1P rate to 2.5V and left to rest for 10 minutes, completing a 1P rate charge-discharge cycle. After 10 1P rate charge-discharge cycles, the battery was disassembled in an argon atmosphere glove box with a moisture content of ≤1ppm to observe whether lithium deposition occurred at the negative electrode interface.

[0190] Table 2 Battery performance test data

[0191] From Table 2 and Figure 1 , it can be seen that, compared with Comparative Example 1, the discharge capacity retention rates of Examples 1 to 40 are all better than that of Comparative Example 1, indicating that the addition of lithium-rich materials supplements the active lithium source during the formation and circulation stages, improves the discharge capacity retention rate of the battery, and optimizes the electrochemical performance of the battery.

[0192] By analyzing Comparative Example 1, Comparative Example 4, Comparative Example 5, Example 4 and Example 5, it can be seen that Comparative Example 1 does not experience lithium plating due to the lack of use of lithium-rich materials. In addition, when the n value is the same, Comparative Example 5, Example 4 and Example 5 all experience no lithium plating. Among them, w in Comparative Example 5, Example 4 and Example 5 is smaller than that in Comparative Example 4, that is, the density w2 of the active material layer of the negative electrode is greater than that in Comparative Example 4. This is because the use of lithium-rich materials may increase the risk of lithium plating during the battery cycle. When the content of lithium-rich materials is too high, the active material layer of the negative electrode cannot provide sufficient lithium storage space. When w is reduced, the density of the negative electrode active material layer is increased, and sufficient lithium storage space can be reserved in the active material layer of the negative electrode to solve the lithium plating problem. Among them, by analyzing the five groups of data of Examples 1 to 3, Examples 4 to 18, Examples 19 to 22, Examples 23 to 27, and Examples 28 to 31, Examples 32 to 37, and Examples 38 to 40, it can be seen that as n shows an incremental change, w shows a decreasing trend, that is, the lithium storage space of the negative electrode active material layer is increased, thereby avoiding the potential risk of lithium plating caused by the increase in n value.

[0193] In combination with Figure 2 and Table 2, it can be seen that compared with Comparative Example 3, the safety levels and discharge capacity retention rates of Examples 1 to 3 and Examples 32 to 34 are higher than those of Comparative Example 3; compared with Comparative Example 5, the safety levels and discharge capacity retention rates of Examples 4 to 18, Example 35, and Example 38 are higher; compared with Comparative Example 6, the safety levels and discharge capacity retention rates of Examples 23 to 27, Example 37, and Example 40 are higher. This is because a cyclic organic sulfide containing a sulfur-oxygen double bond is added as an additive in these embodiments, and the substance participates in the formation of a stable interfacial passivation film on the positive electrode sheet. The stable interfacial passivation film can avoid the dissolution of transition metals or deposition at the negative electrode, thereby helping to improve the safety performance of the battery and improve the electrochemical performance of the battery.

[0194] The safety level and discharge capacity retention rate of Example 23 are both better than those of Comparative Example 7, and the safety level and discharge capacity retention rate of Example 2 are both better than those of Example 1, indicating that the content of cyclic organic sulfides containing sulfur-oxygen double bonds in the electrolyte should match the content of the lithium-rich material. A low content of cyclic organic sulfides containing sulfur-oxygen double bonds cannot compensate for the increased safety risks and poor electrochemical performance caused by the addition of lithium-rich nickel-based materials.

[0195] By comparing the five groups of data of Examples 1 to 3, Examples 4, 5, and 9, Examples 20 to 22, Examples 23 to 25, and Examples 32 to 34, it was found that increasing the content of cyclic organic sulfides containing sulfur-oxygen double bonds can improve the safety of the battery, but when the content of cyclic organic sulfides containing sulfur-oxygen double bonds is too large, the performance of the battery will deteriorate. At this time, the performance of the interfacial passivation film can be optimized by increasing the content of cyclic carbonate in the electrolyte, thereby improving the electrochemical performance of the battery.

[0196] By analyzing the two sets of data of Examples 5 to 8 and Examples 28 to 31, it can be seen that the increase of w1 and w2 will slightly deteriorate the battery performance, but has no effect on lithium plating and safety performance. This is because when w1 and w2 are high, the content of positive and negative active materials is too high and easy to fall off, react with the electrolyte, amplify the occurrence of electrolyte side reactions, and thus have an adverse effect on the electrochemical performance of the battery.

[0197] Test data 2:

[0198] Example 1 was tested using an X-ray diffractometer (D500 Siemens) (λ=0.154 nm), with a scan rate of 4° / min and a CuKα radiation source. XRD data of Example 1 were obtained at different chemical compositions, cycle numbers, and voltages.

[0199] As shown in FIG3 , the characteristic peaks of the lithium-rich nickel base at 36-39°, 42-45° and 43.5-46.5° are consistent with the characteristic peaks of the XRD spectrum measured in Example 1 at these three locations, indicating that the lithium-rich nickel base exists in Example 1.

[0200] In summary, test data 1 and 2 show that adjusting a can control the performance of the passivation film at the interface between the positive and negative electrode sheets, regulating w can improve the problem of lithium plating at the negative electrode sheet, and adding lithium-rich materials can continuously replenish active lithium sources during battery cycling. In other words, when the relationship 0 < 10 × n × w × (6 × an) ≤ 2 holds true, the lithium-rich materials can fully utilize their advantages of continuously replenishing active lithium sources during the use of lithium-ion batteries, improving the electrochemical performance of the batteries and avoiding the adverse effects of transition metal dissolution or deposition at the negative electrode sheet interface during use of the lithium-rich materials on safety performance, thereby increasing the cycle life of the batteries, improving battery cycle performance, and reducing battery safety risks. The discharge capacity retention rate of lithium-ion batteries at 25°C and 1P cycles for 3000 cycles is 90.4% or higher. At the same time, no lithium plating occurs at the negative electrode after 10 cycles at 25°C and 1P, and the overcharge level test is level 3 or higher.

[0201] The above is a detailed introduction to the lithium-ion batteries, battery packs and electrical devices disclosed in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the lithium-ion batteries, battery packs and electrical devices: At the same time, for those skilled in the art, based on the ideas of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present application.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises: a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet to form an electrode assembly, and the electrolyte at least partially infiltrates the electrode assembly; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer comprises a first active material and a second active material of different types, wherein the second active material is a lithium-rich material; the electrolyte comprises a lithium salt, a solvent and an additive, the additive comprises a cyclic organic sulfide containing a sulfur-oxygen double bond; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer comprises a third active material; The lithium-ion battery satisfies the following relationship: 0<10×n×w×(6×an)≤2; Wherein, n is the mass percentage of the second active material in the positive electrode active material layer; The w is the ratio of the surface density of the positive electrode active material layer to the surface density of the negative electrode active material layer; The a is the mass percentage of the cyclic organic sulfide containing sulfur-oxygen double bonds in the electrolyte.

2. The lithium-ion battery according to claim 1, characterized in that The surface density of the positive electrode active material layer is w1, the surface density of the negative electrode active material layer is w2, w is the ratio of w1 to w2, and w satisfies: 1.5≤w≤3.

3. The lithium-ion battery according to claim 2, characterized in that: The w1 satisfies: 0.15 mg / mm 2 ≤w1≤0.3mg / mm 2 , the w2 satisfies: 0.05mg / mm 2 ≤w2≤0.2mg / mm 2 .

4. The lithium-ion battery according to claim 1, characterized in that The n satisfies: 0.5%≤n≤15%.

5. The lithium-ion battery according to claim 1, characterized in that: The a satisfies: 0.1%≤a≤10%.

6. The lithium-ion battery according to claim 1, characterized in that The first active material includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide or lithium nickel cobalt manganese oxide; and / or, The second active material comprises at least one of lithium-rich manganese-based, lithium-rich nickel-based, lithium-rich nickel-cobalt-manganese-based or lithium oxide. a; and / or, The additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, 4-methyl vinyl sulfate, 1,3-propylene glycol cyclic sulfate, ethylene sulfite, methylene methyl disulfonate, 1,4-butane sultone, and 2,4-butane sultone.

7. The lithium-ion battery according to claim 1, characterized in that: The solvent in the electrolyte includes cyclic carbonate, and the mass percentage of the cyclic carbonate in the electrolyte is t2, and t2 and a satisfy: 1≤(t2-0.2) / a≤5.

8. The lithium-ion battery according to claim 7, characterized in that: The t2 meets: 20% <t2≤60%。 9. The lithium-ion battery according to claim 7, characterized in that: The cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, and vinylethylene carbonate.

10. A battery pack, characterized in that: The battery pack comprises a box and a lithium-ion battery as claimed in any one of claims 1 to 9 placed in the box.

11. An electrical device, characterized in that: The electrical device comprises an electrical device body and a lithium-ion battery as claimed in any one of claims 1 to 9 disposed in the electrical device body.

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