CN111092199B - Method for simultaneously improving over-discharge capacity, low-voltage discharge capacity and storage performance of lithium battery - Google Patents

Abstract

The invention discloses a method for simultaneously improving the over-discharge capacity, the low-voltage discharge capacity and the storage performance of a lithium battery, wherein the lithium battery comprises an anode, a cathode and electrolyte, the anode comprises an anode active material, and the cathode comprises a cathode active material, wherein the first coulombic efficiency of the cathode active material is at least 2.8% higher than that of the anode active material. According to the invention, the electrode material with the first effect of the negative active material higher than that of the positive active material is selected when the battery is designed and screened, so that the first coulombic efficiency of the negative active material is at least 2.8% higher than that of the positive active material, the negative electrode has more active lithium, a discharge platform can be arranged between 1.0-1.5V of the low voltage represented by a battery curve, and the over-discharge capacity, the low-voltage discharge capacity and the storage performance of the lithium battery can be simultaneously improved.

Description

Simultaneously improve the method of lithium battery over-discharge capacity, low-voltage discharge capacity and storage performance

technical field

The invention relates to the field of lithium-ion batteries, in particular to a method for simultaneously improving the lithium battery's over-discharge capability, low-voltage discharge capability and storage performance.

Background technique

As an internationally recognized ideal chemical energy source, lithium-ion batteries have the advantages of small size, large capacity, and high voltage, and are widely used in electronic products such as mobile phones and laptop computers. In recent years, the market demand for new lithium-ion batteries not only requires high energy density and long-term cycle stability, but also requires high power density, high-rate discharge capability and long-term storage performance, so that it can be used in pure electric vehicles, hybrid electric vehicles and applications such as power tools.

During the actual use and storage of the battery, there will always be over-discharge: if the battery is discharged at a high rate for a long period of time, it will easily cause the over-discharge phenomenon of the battery, which will accelerate the shortening of the battery life. Another example is the phenomenon of improper use: 3C products or electric tools are discharged, and users often force restart the electrical appliances. It is equivalent to forcing the battery to over-discharge with a large current, which will cause a rapid decline in battery life. Also, when the battery is used in an electric vehicle, multiple batteries must be connected together to form a string, and then connected in series to form a module and assembled into a battery pack. No matter how the production is controlled, there is always a problem with the consistency of the battery. Even if the consistency of the fresh battery is very good, the problem of battery consistency will appear as the cycle progresses. In either case, it is inevitable that one or more batteries will be over-discharged. When over-discharge occurs, the most dangerous thing is that the battery voltage is close to or even reaches 0V. At this time, the potential of the negative electrode usually rises to the potential of copper precipitation (about 3.5V), and the potential of the positive electrode is also easy to drop to the potential of aluminum dissolution (about -1V). The precipitated copper or the re-reduced aluminum after dissolution will pierce the diaphragm and cause a serious internal short circuit, which reduces the life of the battery pack and easily causes safety hazards.

In order to improve the over-discharge resistance of lithium-ion batteries, there are three methods commonly used in the prior art: (1) Protecting the battery by using a protection circuit. For example, CN101159375A discloses a lithium battery power supply control and protection circuit and control and protection method. By detecting the battery voltage, the power supply of the battery is controlled to prevent over-discharge, and the circuit and method can completely shut down the battery through software. The circuit consists of a voltage comparison module (1), a software shutdown detection module (2), a hardware shutdown detection module (3), and a hardware startup detection module (4); among them, the voltage comparison module uses a voltage detection chip of the model HT7027 (U1), one end of the voltage detection chip is connected to one end of the shutdown button (S2) in the hardware shutdown detection module (3), and the switch transistor (Q1) in the hardware shutdown detection module (3) is connected to the switch transistor (Q1) of the activation button (S1). The emitters are connected, the emitter of the switching transistor (Q1) is the battery input terminal, and the collector is the battery output terminal; the input terminal of the shutdown transistor (Q3) in the software shutdown detection module is connected to the control pin of the microcontroller, and the output terminal is connected to the voltage Check the output pin of the chip. However, the cost of using a protection circuit is relatively high, and the use of a protection circuit cannot delay or prevent potential safety hazards that occur when the cell is over-discharged to close to 0V. (2) Additional introduction of over-discharge protection additives. For example, CN103840130A discloses a lithium battery carbon negative electrode that prevents overdischarge, which is used to solve the problem that the existing carbon negative electrode capacity is exhausted, the potential will rise rapidly, and then the dissolution of copper in the negative electrode current collector and the precipitation on the surface of the positive electrode will occur. The invention includes a current collector, the two sides of the current collector are coated with a vacuum-dried negative electrode slurry layer, and the negative electrode slurry layer is formed by mixing carbon active materials, over-discharge functional additives, conductive agents and binders; over-discharge The functional additive is lithium titanate. The invention enables the carbon negative electrode battery to still have a part of capacity after the discharge lower limit voltage, thereby avoiding the dissolution and precipitation of current collector copper caused by over-discharge, and improving the storage life and service life of the battery. CN105304859A discloses a negative electrode of a lithium ion battery and a preparation method thereof, and a lithium ion battery containing the negative electrode of the lithium ion battery. The negative electrode active material layer on the anti-over-discharge coating; the anti-over-discharge coating is composed of lithium titanate and a binder, and the chemical formula of the lithium titanate is LixTi5O12, where 4≤x≤9. The preparation method of the negative electrode of the lithium ion battery includes: 1) mixing lithium titanate with a binder and a solvent to prepare a slurry; coating the slurry on the surface of the negative electrode current collector, drying and rolling to obtain a surface with The current collector of the anti-over-discharge coating; 2) coating the negative electrode slurry on the surface of the current collector with the anti-over-discharge coating on the surface obtained in step (1), and drying and rolling to obtain the negative electrode of the lithium ion battery. The negative electrode of the lithium ion battery provided by the present invention can effectively avoid the decomposition of the SEI film in the overdischarge state of the lithium ion battery by providing an anti-overdischarge coating layer containing lithium titanate between the current collector and the negative electrode active material layer, and At the same time, it solves the problem that the existing negative current collector is easy to oxidize and dissolve under the state of over-discharge of the battery. However, the additional introduction of over-discharge protection additives is carried out through a low first effect and low discharge voltage platform, but it is also difficult to synthesize, high cost and poor cycle performance, which restricts its application. (3) Add additives that can generate redox couples under low voltage for over-discharge protection. However, this method is usually a one-time protection. Once the additive is oxidized and reduced on the surface of the negative electrode, this situation is irreversible, resulting in irreversible battery capacity and end of life. It can be seen that the technical solutions of these methods in the prior art are complex and cannot solve the battery over-discharge problem well.

In order to improve the storage performance of lithium-ion batteries, there are generally two methods in the prior art: one is to store at low SOC and lower temperature to reduce the consumption of lithium in high SOC state and high temperature acceleration; the other is to add SEI to form a film The agent makes the SEI more stable and less likely to be damaged during storage, so as to reduce the consumption of active lithium. However, because the active lithium is always inevitably consumed, the effects of the above methods are not obvious.

Therefore, there is an urgent need for a method that can simultaneously improve the over-discharge resistance, low-voltage discharge capacity, and storage performance of lithium-ion batteries without adding additional additives, so as to suppress the problem of rapid expansion of battery differentiation, thereby improving the service life of battery packs. .

Contents of the invention

In order to make up for the defects of the prior art, the present invention provides a method for improving the over-discharge capacity, low-voltage discharge capacity and storage performance of lithium batteries at the same time. By simply matching the first effect of the electrode material, the storage capacity can be improved while the over-discharge capacity is improved. performance, with great production value.

The technical problem to be solved by the present invention is realized through the following technical solutions:

A method for improving the over-discharge capability, low-voltage discharge capability and storage performance of a lithium battery at the same time, the lithium battery includes a positive electrode, a negative electrode and an electrolyte, the positive electrode contains a positive electrode active material, and the negative electrode contains a negative electrode active material, wherein the negative electrode is active The first Coulombic efficiency of the material is at least 2.8% higher than the first Coulombic efficiency of the positive electrode active material.

Further, the discharge platform voltage of the lithium battery is 1.0V-1.5V.

Further, the first coulombic efficiency of the positive electrode active material is 70%-91%; the first coulombic efficiency of the negative electrode active material is 85%-95%.

Further, the positive electrode active material is a material capable of intercalating lithium under low voltage; the negative electrode active material is one or more of graphite, tin alloy, silicon-oxygen composite material or silicon-carbon composite material.

Further, the positive electrode active material is a nickel-rich ternary material with a layered structure.

Further, the chemical formula of the nickel-rich ternary material with a layered structure is LiNi _x M _1-x O ₂ , wherein M is at least one of Co, Mn, and Al, and 0.5≤x≤1.

Further, the positive electrode active material is LiMn ₂ O ₄ with a spinel structure.

Further, the electrolyte contains SEI film-forming additives accounting for 0.5-2% of the total mass of the electrolyte.

Further, the SEI film-forming additive is vinylene carbonate.

Further, the N/P ratio of the positive electrode and the negative electrode is 1.02-1.2.

The present invention has following beneficial effect:

The present invention adopts the electrode material whose first effect of the negative electrode active material is higher than that of the positive electrode active material when designing and screening materials for the battery, so that the first coulombic efficiency of the negative electrode active material is at least 2.8% higher than the first coulombic efficiency of the positive electrode active material , so that the negative electrode has more active lithium, which can make the battery curve show a discharge platform between the low voltage of 1.0-1.5V, which can simultaneously improve the over-discharge capacity, low-voltage discharge capacity and storage performance of the lithium battery.

The method of the invention can effectively improve the over-discharge resistance of the lithium battery under the condition that the negative electrode does not separate copper; the invention can have a discharge platform between the low voltage of 1.0-1.5V, which can increase the discharge capacity of the battery at low voltage , broaden the battery voltage window. The invention can effectively improve the storage performance of the battery, and increase the storage capacity recovery rate and capacity retention rate.

The present invention does not introduce over-discharge protection additives and does not increase additional processes and costs. The method can quickly screen out electrode active materials and match them, which can save a lot of development costs.

Description of drawings

Fig. 1 is the over-discharge comparison diagram of the first coulombic efficiency difference of different positive and negative active materials of the present invention;

Fig. 2 is over-discharge cycle diagram in embodiment 1 and comparative example 1;

Fig. 3 is over-discharge capacity retention figure in embodiment 1 and comparative example 1;

FIG. 4 is a diagram of storage capacity recovery rates in Example 1 and Comparative Example 1. FIG.

Detailed ways

Raw materials used in the present invention, equipment, if not specified, are commonly used raw materials, equipment in this area; Method used in the present invention, if not specified, are conventional methods in this area.

Unless otherwise specified, the meanings of the terms in this specification are the same as those generally understood by those skilled in the art, but if there is any conflict, the definitions in this specification shall prevail.

Herein "comprises", "comprising", "comprising", "containing", "having" or other variations thereof are intended to cover non-closed inclusions and no distinction is made between these terms. The term "comprising" means that other steps and ingredients can be added which do not affect the end result. The term "comprising" also includes the terms "consisting of" and "consisting essentially of". The compositions and methods/processes of the present invention comprise, consist of and consist essentially of the essential elements and limitations described herein and any additional or optional ingredients, components, steps or limitations described herein.

All numbers or expressions referring to amounts of components, process conditions, etc. used in the specification and claims are to be understood as modified by "about" in all instances. All ranges referring to the same component or property are inclusive of endpoints, which are independently combinable. Since these ranges are continuous, they include every value between the minimum and maximum values. It should also be understood that any numerical range recited herein is intended to include all subranges within that range.

As described in the background art, there is no suitable method in the prior art that can simultaneously improve the over-discharge resistance, low-voltage discharge capacity and storage performance of lithium-ion batteries without adding additional additives. In order to solve the above technical problems, the inventors have found through a lot of research that simply matching the first effect of the positive active material and the negative active material can improve the storage performance while improving the over-discharge capability, which has great production value.

A method for improving the over-discharge capability, low-voltage discharge capability and storage performance of a lithium battery at the same time, the lithium battery includes a positive electrode, a negative electrode and an electrolyte, the positive electrode contains a positive electrode active material, and the negative electrode contains a negative electrode active material, wherein the negative electrode is active The first Coulombic efficiency of the material is at least 2.8% higher than the first Coulombic efficiency of the positive electrode active material.

In the prior art, the first Coulombic efficiency of the positive electrode active material and the first Coulombic efficiency of the negative electrode active material are often very close. The inventors have found through a lot of research that the first Coulombic efficiency of the negative electrode active material is at least higher than the first Coulombic efficiency of the positive electrode active material. 2.8% higher, can simultaneously improve lithium battery over-discharge capacity, low-voltage discharge capacity and storage performance, which is a technical effect that those skilled in the art cannot expect from the prior art. The present invention has been accomplished based on the above findings and recognitions.

In the present invention, the first Coulombic efficiency of the negative electrode active material is at least 2.8% higher than the first Coulombic efficiency of the positive electrode active material, so that the negative electrode can have more active lithium, and too much lithium can be inserted into the layered The surface layer of the positive electrode forms a new phase of Li ₂ MO ₂ type, in which M is transition metal elements such as Ni, Co and Mn, which can realize the discharge of the battery at low voltage. The battery curve shows that there is a discharge platform between the low voltage 1.0-1.5V, which prevents the negative electrode potential from being too high, thereby improving its over-discharge resistance performance. At the same time, because the excess active lithium is stored in the negative electrode, more lithium is provided for consumption during the storage process of the battery, preventing the consumption of more active lithium, so the storage performance of the battery is improved, especially the storage performance at low voltage. . This method improves the over-discharge resistance and storage performance of the battery without introducing over-discharge additives, without introducing additional processes and costs, and provides guidance for screening positive and negative active materials, which has great practical significance .

The inventor found in the research that even if the first Coulombic efficiency of the negative active material is greater than the first Coulombic efficiency of the positive active material, the difference between the first Coulombic efficiency of the negative active material and the first Coulombic efficiency of the positive active material is within 2.8%. At this time, most of the extra active lithium is used for the SEI film, which has no obvious effect on improving the over-discharge capacity, low-voltage discharge capacity and storage performance of the lithium battery.

In the present invention, the discharge platform voltage of the lithium battery is 1.0V-1.5V. In the present invention, there is a discharge platform between the low voltage 1.0-1.5V. The formation of this discharge platform is due to the loss of the first effect of the battery composed of the positive electrode and the negative electrode, and the redundant active lithium in the negative electrode is re-embedded into the positive electrode material. A new phase of Li ₂ MO ₂ type is formed on the surface, and M is transition metal elements such as Ni, Co and Mn. Because of the formation of this new phase, the coordination structure of the lithium layer on the surface and subsurface of the positive electrode material changes from the original lithium octahedral coordination to the lithium tetrahedral coordination. This structural transformation enables the positive electrode material to have a low-voltage delithiation platform, so that the battery has a low potential of the negative electrode when the full battery open voltage is lower than 1.5V. Prevent the full battery at the end of over-discharge, the negative electrode potential is too high. Because the new phase Li ₂ MO ₂ has a certain degree of reversibility, the full battery has a strong ability to suppress the potential rise of the negative electrode during cycling and a good ability to withstand over-discharge. Having a discharge platform between the low voltage 1.0-1.5V means that the battery has extra active lithium in the voltage window of the conventional platform such as 2.75-4.2V. This part of lithium can be used to consume lithium due to the continuous formation of the SEI film during battery storage, thereby improving the storage performance of the battery.

The first coulombic efficiency of the positive electrode active material is 70%-91%, such as 70%, 72%, 75%, 78%, 80%, 82%, 84%, 86%, 88%, or 91%, Or an interval range formed by these values.

The first Coulombic efficiency of the negative electrode active material is 85%-95%, for example, it may be 85%, 87%, 89%, 91%, 93%, or 95%, or an interval range formed by these values.

The first coulombic efficiency of active materials is usually closely related to the type of material, the proportion of elements, the synthesis method and process, whether it is doped or not, and whether it is coated or not. In order to make the first coulombic efficiency of the negative active material at least 2.8% higher than that of the positive active material, the inventors screened the positive and negative active materials in the prior art. In the present invention, the positive electrode active material is a material that can intercalate lithium at low voltage, and by selecting a material that can intercalate lithium at low voltage as the positive electrode active material, electrochemical lithium intercalation behavior can occur at low voltage to generate _a new type of _Li2MO2 phase, and M is transition metal elements such as Ni, Co and Mn. As an example, the positive electrode active material may be a high-nickel ternary material with a layered structure, wherein the chemical formula of the high-nickel ternary material with a layered structure is LiNi _x M _1-x O ₂ , where M is Co , at least one of Mn, Al, 0.5≤x≤1; the positive electrode active material can also be LiMn ₂ O ₄ with a spinel structure.

The negative electrode active material is one or more of graphite, tin alloy, silicon-oxygen composite material or silicon-carbon composite material. More preferably, in order to pursue a battery with high energy density, the negative electrode active material is graphite and silicon-oxygen composite material, more preferably, the negative electrode active material is graphite and silicon-carbon composite material.

It should be noted that, in addition to the positive electrode active material, the positive electrode also includes a positive electrode conductive agent and a positive electrode binder. The present invention does not specifically limit the type and amount of the positive electrode conductive agent and the positive electrode binder, and the type and conventional addition amount well known to those skilled in the art will suffice.

It should be noted that, in addition to the negative electrode active material, the negative electrode also includes a negative electrode conductive agent and a negative electrode binder. The present invention does not specifically limit the type and amount of the negative electrode conductive agent and the negative electrode binder, and the types and conventional addition amounts well known to those skilled in the art will suffice.

The electrolyte contains SEI film-forming additives accounting for 0.5-2% of the total mass of the electrolyte. In the present invention, by adding an SEI film-forming additive, the consumption of active lithium during film formation can be further reduced, and the remaining amount of active lithium in the negative electrode can be increased.

In the present invention, the types of SEI film-forming additives are not specifically limited, and SEI film-forming additives well known to those skilled in the art can be used. Those skilled in the art can select and adjust according to actual production conditions, product requirements and quality requirements . As an example, the SEI film-forming additive is vinylene carbonate (VC).

It should be noted that in addition to containing SEI film-forming additives in the electrolyte, it also contains various components that it usually contains. These are known to those skilled in the art through technical manuals or through conventional experimental methods. The present invention does not These components are improved and will not be repeated here.

In the present invention, the N/P ratio of the positive electrode and the negative electrode is 1.02-1.2. In the present invention, the N/P ratio of the positive electrode and the negative electrode is controlled within the range of 1.02-1.2 to prevent the negative electrode from decomposing lithium. If it exceeds this range, a film will be formed on the surface of the material and more lithium will be consumed.

The present invention will be described in detail below in conjunction with examples, which are only preferred implementations of the present invention, and are not limitations of the present invention.

Example 1

A method for simultaneously improving over-discharge capability, low-voltage discharge capability and storage performance of a lithium battery, wherein the lithium battery includes a positive electrode, a negative electrode and an electrolyte; the positive electrode includes a positive electrode active material, and the positive electrode active material is high nickel with a layered structure Ternary material, the chemical formula of the high-nickel ternary material with layered structure is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; the first coulombic efficiency of the positive electrode active material is 87%; the negative electrode contains the negative electrode active material, so The negative active material is artificial graphite mixed with 5% silicon-carbon composite material; the first coulombic efficiency of the negative active material is 92.1%; the first coulombic efficiency of the negative active material is higher than the first coulombic efficiency of the positive active material 5.1% out.

The N/P ratio of the positive and negative electrodes was 1.05.

The winding core of the lithium battery is made by a positive electrode, a negative electrode, and a separator by a winding process or a stacking process; the discharge platform voltage of the lithium battery is 1.0V-1.5V.

The electrolyte contains 0.5-2% of SEI film-forming additive accounting for the total mass of the electrolyte, and the SEI film-forming additive is vinylene carbonate (VC).

Example 2

A method for simultaneously improving over-discharge capability, low-voltage discharge capability and storage performance of a lithium battery, wherein the lithium battery includes a positive electrode, a negative electrode and an electrolyte; the positive electrode includes a positive electrode active material, and the positive electrode active material is high nickel with a layered structure Ternary material, the chemical formula of the high-nickel ternary material with a layered structure is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ; the first Coulombic efficiency of the positive active material is 70%; the negative electrode contains the negative active material, so The negative active material is artificial graphite mixed with 5% silicon-oxygen composite material; the first coulombic efficiency of the negative active material is 85%; wherein the first coulombic efficiency of the negative active material is higher than the first coulombic efficiency of the positive active material 15% higher.

The N/P ratio of the positive and negative electrodes was 1.02.

The winding core of the lithium battery is made by a positive electrode, a negative electrode, and a separator by a winding process or a stacking process; the discharge platform voltage of the lithium battery is 1.0V-1.5V.

The electrolyte contains 0.5% of the SEI film-forming additive accounting for the total mass of the electrolyte, and the SEI film-forming additive is vinylene carbonate (VC).

Example 3

A method for simultaneously improving the over-discharge capability, low-voltage discharge capability and storage performance of a lithium battery, wherein the lithium battery includes a positive electrode, a negative electrode and an electrolyte; the positive electrode includes a positive electrode active material, and the positive electrode active material is LiMn with a spinel structure ₂ O ₄ ; the first coulombic efficiency of the positive active material is 91%; the negative electrode includes a negative active material, and the negative active material is artificial graphite mixed with 5% tin alloy; the first coulombic efficiency of the negative active material 95%; wherein the first Coulombic efficiency of the negative active material is 7% higher than the first Coulombic efficiency of the positive active material.

The N/P ratio of the positive and negative electrodes was 1.2.

The winding core of the lithium battery is made by a positive electrode, a negative electrode, and a separator by a winding process or a stacking process; the discharge platform voltage of the lithium battery is 1.0V-1.5V.

The electrolyte contains an SEI film-forming additive accounting for 2% of the total mass of the electrolyte, and the SEI film-forming additive is vinylene carbonate (VC).

Comparative example 1

A lithium battery, the lithium battery includes a positive pole, a negative pole and an electrolyte; the positive pole contains a positive active material, the positive active material is a high-nickel ternary material with a layered structure, and the high-nickel ternary material with a layered structure The chemical formula of the nickel ternary material is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; the first coulombic efficiency of the positive electrode active material is 83.3%; the negative electrode contains the negative electrode active material, and the negative electrode active material is artificial graphite mixed with 5% For the silicon-carbon composite material, the first Coulombic efficiency of the negative active material is 83.5%; the first Coulombic efficiency of the negative active material is 0.2% higher than the first Coulombic efficiency of the positive active material.

The N/P ratio of the positive and negative electrodes was 1.05.

The winding core of the lithium battery is made by a positive electrode, a negative electrode, and a diaphragm by a winding process or a stacking process.

The electrolyte contains 0.5-2% of SEI film-forming additive accounting for the total mass of the electrolyte, and the SEI film-forming additive is vinylene carbonate (VC).

Comparative example 2

A lithium battery, the lithium battery includes a positive pole, a negative pole and an electrolyte; the positive pole contains a positive active material, the positive active material is a high-nickel ternary material with a layered structure, and the high-nickel ternary material with a layered structure The chemical formula of the nickel ternary material is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ; the first coulombic efficiency of the positive electrode active material is 89.7%; the negative electrode contains the negative electrode active material, and the negative electrode active material is artificial graphite mixed with 5% For the silicon-carbon composite material, the first Coulombic efficiency of the negative active material is 92.5%; the first Coulombic efficiency of the negative active material is 2.8% higher than the first Coulombic efficiency of the positive active material.

The N/P ratio of the positive and negative electrodes was 1.05.

The winding core of the lithium battery is made by a positive electrode, a negative electrode, and a diaphragm by a winding process or a stacking process.

The electrolyte contains 0.5-2% of SEI film-forming additive accounting for the total mass of the electrolyte, and the SEI film-forming additive is vinylene carbonate (VC).

test case

The lithium batteries of Example 1 and Comparative Example 1-2 were overcharged from a full charge state of 4.2V to 0.5V to obtain a voltage-capacity curve, thereby obtaining a capacity-voltage curve, as shown in Figure 1, when the positive and negative active materials are first When the difference of Coulomb efficiency is 2%, there is an inconspicuous platform, and when the difference reaches 5%, the low-voltage discharge platform is obvious.

In order to verify the performance of the product of the present invention, relevant performance tests were carried out on the lithium batteries prepared in Example 1 and Comparative Examples 1-2, the specific methods are as follows:

(1) Over-discharge resistance test

Put the lithium-ion battery in a normal temperature environment for charge-discharge over-discharge cycle test. The cycle voltage window is 0.5-4.2V, the charge current is 0.5C, the cut-off current is 0.05C, and the discharge current is 1C.

The test results are shown in Figure 2. The rate of decay of the lithium battery in Example 1 is less than that of the lithium battery in Comparative Example 1; after 100 cycles, the capacity retention rate of the lithium battery in Example 1 is 91.6%. The capacity retention rate of lithium batteries is 88.5%. The first coulombic efficiency of the negative active material is 5.1% higher than that of the positive active material. A lithium-ion battery has a lower discharge voltage platform, which prevents the negative electrode potential from being too high and copper dissolution in the end of discharge, and also makes the battery have Ability to discharge at low voltage.

(2) Capacity retention test

Lithium batteries were placed in a constant temperature environment of 25±2 and 45±2°C for long-term full-charge storage tests at room temperature and high temperature. Capacity retention test method: After storage, place the lithium battery at room temperature for 3 hours, then discharge to obtain the residual capacity of the battery; the ratio of the residual capacity to the initial capacity is the capacity retention rate. As shown in Figure 3, after storage at room temperature for 100 days, the capacity retention rates of the lithium batteries in Example 1 and Comparative Example 1 were 101.9% and 98.9%, respectively, and the capacity retention rates of the lithium batteries in Example 1 and Comparative Example 1 were 250 days. The ratios are respectively 100.7% and 97.2%; the capacity retention ratios of the lithium batteries in Example 1 and Comparative Example 1 are respectively 98.3% and 96.6% in high temperature storage for 100 days, and the capacity retention rates of the lithium batteries in Example 1 and Comparative Example 1 are 250 days. The capacity retention rates were 94.7% and 91.1%, respectively. Because the high-temperature environment will accelerate the consumption of active lithium, the lithium battery in Example 1 contains more redundant active lithium, so it has better high-temperature storage performance.

(3) Storage recovery rate test

Lithium batteries were placed in a constant temperature environment of 25±2 and 45±2°C for long-term full-charge storage tests at room temperature and high temperature. Capacity recovery rate test method: After storage, place the lithium battery at room temperature for 3 hours, discharge it, and then charge and discharge it 3 times to obtain the recovery capacity; the ratio of the recovery capacity to the initial capacity is the storage recovery rate. As shown in Figure 4, the storage recovery rates of the lithium batteries in Example 1 and Comparative Example 1 stored at room temperature for 100 days were 100.4% and 97.8% respectively, and the storage recovery rates of the lithium batteries in Example 1 and Comparative Example 1 for 250 days 100.3% and 95.8% respectively; the storage recovery rate of the lithium battery in Example 1 and Comparative Example 1 in high temperature storage for 100 days was 99.8% and 97.2% respectively, and the storage recovery rate of the lithium battery in 250 days Example 1 and Comparative Example 1 The recovery rates were 97.6% and 93.4%, respectively. It can be seen from the above that the excess active lithium also helps to improve the capacity recovery rate of stored lithium.

The above-described embodiments only express the implementation manner of the present invention, and its description is more specific and detailed, but it should not be interpreted as limiting the scope of the patent of the present invention, as long as the technical solutions obtained in the form of equivalent replacement or equivalent transformation are adopted , should fall within the protection scope of the present invention.

Claims (1)

1. The method simultaneously improves the over-discharge capacity, the low-voltage discharge capacity and the storage performance of the lithium battery, wherein the lithium battery comprises a positive electrode, a negative electrode and electrolyte; the positive electrode comprises a positive electrode active material which is a high-nickel ternary material with a layered structure,

the chemical formula of the high-nickel ternary material with the laminated structure is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (ii) a The first coulombic efficiency of the positive active material is 87%; the negative electrode comprises a negative electrode active material, and the negative electrode active material is a silicon-carbon composite material mixed with 5% of artificial graphite; the first coulombic efficiency of the negative active material is 92.1%; the first coulombic efficiency of the negative electrode active material is 5.1% higher than that of the positive electrode active material; the ratio of N/P of the positive electrode to the negative electrode is 1.05; the winding core of the lithium battery is prepared by a winding process or a lamination process for the anode, the cathode and the diaphragm; the discharge platform voltage of the lithium battery is 1.0V-1.5V; the electrolyte contains SEI film forming additive accounting for 0.5-2% of the total mass of the electrolyte, and the SEI film forming additiveThe film forming additive is vinylene carbonate; or,

the chemical formula of the high-nickel ternary material with the laminated structure is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (ii) a The first coulombic efficiency of the positive electrode active material is 70%; the negative electrode comprises a negative electrode active material, and the negative electrode active material is a silica composite material mixed with 5% of artificial graphite; the first coulombic efficiency of the negative active material is 85%; wherein the first coulombic efficiency of the negative active material is 15% higher than that of the positive active material; the ratio of N/P of the anode and the cathode is 1.02; the winding core of the lithium battery is prepared by a winding process or a lamination process for the anode, the cathode and the diaphragm; the discharge platform voltage of the lithium battery is 1.0V-1.5V; the electrolyte contains an SEI film forming additive which accounts for 0.5 percent of the total mass of the electrolyte, and the SEI film forming additive is vinylene carbonate.

Images